Something Completely Different - Metal Bowls - and a Colascione

Some years ago while working for a period earning a living as a heritage tinsmith, I made a copy of a 19th C French guitar by Grobert entirely in tin-plate complete with brass strings. It was not intended to be played - just for display as a demonstration of the tinsmith's craft.

This time around I thought that it would be interesting to make a working instrument with a metal bowl. Why? - just because I can (or once could when eyes were clearer and hands steadier!).
The instrument that I plan to make is a Colascione - a long necked lute that was introduced to Europe from Turkey via Italy it is thought around the mid 15th C - and prevailed in Italy as a popular folk instrument until recent times. This instrument has been chosen because the bowl is relatively small in size so will be a bit easier (and safer) to handle during the fabrication process - compared to say a full sized oud or lute.

As I have measurements on file of a surviving 17th C Colascione (the Dean Castle Collection, Scotland) it will be used as a basis for this project. The Dean Castle Colascione has an ivory bowl, 3 strings and a string length of 75.6 cm. - clearly a costly instrument in its day no doubt made for a rich dilettante rather than a street musician. This is a mid sized or Mezzo-Colascione. See attached images.

Some earlier discussion about the possible origins of the European Colascione is posted here on the forum:

http://www.mikeouds.com/messageboard/viewthread.php?tid=7096#pid438...

The attached engraving by Marin Mersenne, 1636 compares the European version of his time with a Middle Eastern counterpart.

The bowl section is semicircular with wider side ribs to increase the overall depth. To simplify the fabrication work the number of ribs has been reduced to a total of 9 from the original 15. Once the metal bowl has been fabricated the neck and end blocks (of wood) will be 'retrofitted' and glued into place. Also a conventional wooden end clasp and side strips will be glued to the exterior surface as on the original. These components provide wooden joint surfaces required for attachment of the sound board - necessary for thin ivory (less than 1mm thick) as well as thinner tinplate.

As the bowl section is semicircular the central ribs will all be identical and symmetrical. A pattern for the ribs was created first by drawing a full size section of the bowl to determine the maximum rib width and included angle between the ribs. A rib former was then made by cutting two half sections of the sound board profile from thin Masonite, hinged together with adhesive tape and set at the included angle (21°) with wooden blocks glued in place.
The required rib profile is then represented by the inside edges of the former.
The rib profile is then traced onto a paper strip taped over the the former and the edges rubbed with a fingertip tipped in graphite powder (or rubbed with a pencil).

The rib pattern on the paper strip is then taped to a sheet of tinplate and the rib profile carefully cut out with a sharp knife. The knife transfers the rib profile onto the tinplate as a fine cut line in the surface.
The rib pattern is then cut out using hand shears or tin snips following the scribed line exactly - not as easy as it might first appear requiring practice, good lighting, good eyesight and a steady hand.
Any slight wrinkling of the cut edges is then removed by dressing with a smooth faced hammer on an anvil.

The accuracy of the pattern is all important and must allow for any potential cumulative errors during the course of fabrication as these cannot be corrected as work proceeds (as they can with wooden rib construction).

An essential tool for soldering tinplate is a temperature controlled soldering iron - a cheap soldering iron that can reach temperatures in excess of 1000°F (535°C) will burn the tin coating.
The best tool for the job is made by the 'Weller' company (W60P - W100P series). Temperature is controlled by an ingenious system that depends upon loss of magnetism of a magnet at a critical temperature (the Curie Temperature). In the 'Weller' iron this phenomenon is used to operate a switch to turn off power when the tip of the iron reaches a fixed temperature (600°F, 700°F and 800°F) dictated by a ferromagnetic sensor in the tip.

For this project I will be using a Weller W60P iron with a 1/4 inch chisel tip operating at 700°F.

Having made the rib pattern the ribs are marked out by tracing around the pattern placed on a sheet of tinplate using a sharp pointed scriber. Each rib is then accurately cut out by hand with tinsnips and the edges dressed smooth with a hammer - as described for making the pattern.
Each rib is then easily bent by hand to roughly the required contour (the sound board profile).
No mould is required to fabricate the bowl. Each pair of ribs is held edge to edge and 'tacked' in position with spots of solder - working along the length of each rib joint from one end to the other.
Once each rib has been tacked the joint on both sides is coated with a thin film of acid paste flux and the soldering iron is then run the full length of the interior surface melting the spots of solder as it goes into a solid homogeneous joint.
The attached image shows the first three ribs assembled.

The ribs are now assembled and trimmed to form the basic bowl. Total time to reach this stage would be an afternoon's work - say about six hours for a relatively experienced worker starting with marking out the ribs.

As the weather has turned frigid it is currently not comfortable to work in my workshop so this will be a good time to assess the structural viability or otherwise of the bowl and to decide whether or not to proceed further with this little project.

The rib joints are very thin (about 0.4 mm) and relatively fragile so can separate if the bowl, in its current state, is subject to flexing. Some additional joint reinforcement might, therefore, be worthwhile as a precaution. First thoughts would be to reinforce each joint with small soldered tabs of tinplate spaced at say 5 cm intervals along the joint. We will see.

The main additional structural component is a baffle plate located at the neck block position. This has been cut from tin plate and soldered in position. The little soldering tabs on the baffle were cut using a 'nibbler' or 'notcher' tool that can cut where tin snips cannot go (a tool used by electronics workers for hand cutting circuit boards). The space behind the baffle will be filled with wood slices epoxy glued in place as a retrofitted neck block.
Total weight of the completed metal bowl is 320 grams.

Apart from the wooden neck block, wooden strips are to be epoxy glued around the upper edge of the bowl to provide a gluing surface for the sound board. Assembly of the sound board to bowl and other wooden components of the rest of the instrument will then use conventional hot hide glue.

Another historical reference to the colascione is found in 'Musurgia Universalis' by Athanasus Kircher, Rome 1650.

The attached image shows a three string colascione (here named a colachon) alongside a theorbo - the colascione being a longer instrument (assuming that they are engraved to about the same scale). Oddly the tuning of the colascione is given as c', c'' and g'' which means that if strung in gut string length would have to be about 30 cm or so - hardly a bass continuo instrument!

The fret spacings are interesting if drawn proportionally to scale.

Now that the metal work of the bowl is complete the wooden interfaces - neck block, tail block, end clasp and side strips - must be configured, shaped and glued in place.

The neck block is made from 9 mm thick slices of 'yellow poplar' (it is not a poplar but a species of magnolia tree) - rescued years ago from an old desk found thrown in a 'dumpster'. This is a relatively soft but stable and easily carved wood. Each slice was sawn out roughly to size with a coping saw and then shaped to fit by carving with a knife and finished with a small woodworking rasp. Grain direction of the slices is arranged to cross like plywood. High precision of the fit is not required as the slices will be glued in place with gap filling epoxy.

The block is left well oversize for final trimming after all of the other wooden additions to the bowl are finally in place.

Further research reveals that there is one surviving manuscript of music for colascione - or rather the 'soprano' version known as the colascioncino tuned an octave higher than the larger colascione (its string length being about 50 cm). Domenico Colla and his brother Bresciani toured Europe giving recitals during the second half of the 18th C - Domenico being a virtuoso player of the 2 string colascioncino (played with a wood bark plectrum) . There are six sonatas written for the instrument with bass accompaniment (colascione or guitar?) - a some pages from the sonatas are attached for information. Fancy stuff - I could not find recordings on YouTube - too difficult for modern performers perhaps?

This attempt to present the colascione as a high art instrument appears to have failed, the instrument being then regarded as a curiosity by the audiences although the skill of the performers was appreciated.

See FoMRHI Comm 2027 - link on page 5 of this topic.

Due to the curvature of the end of the bowl it has been decided to make the wooden clasp in three main section to obtain a close fit.
The lower part of the clasp is to be made in segments hot bent to fit the curvature of the bowl with ebony lines between the segments. Not sure how this will work out.
A rubbing on paper was first made of the end of the bowl to determine the approximate size and geometry of the segments.
The ebony lines were easily bent on the attachment to my propane heated bending iron - specifically designed for bending lines and purfling. Ebony is brittle so plenty of heat is required with gentle persuasion to avoid breakage.
The attached image shows the clasp segments, with lines glued in place, roughly assembled. These will now be fitted and glued together on the bowl before final trimming and shaping.

All a bit fancy to set off against the plain metal of the bowl.


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To obtain a close fit to the bowl, the segments of the clasp lower section must be fitted and glued together on the bowl itself.
The bowl was first covered with kitchen KlingWrap plastic film as protection and the individual segments cut to size, joints planed flat and glued together piece by piece using adhesive tape to hold everything together as work proceeded. A bit like making an oud or lute bowl.
Fish glue was used as a strong quick drying adhesive - soluble in water so adjustments can be made in the event of any inaccurate fit. This is a tricky fitting and assembly task hence the benefit of using ebony lines at the joints to disguise any slight discrepancies - an old luthier secret! In the event only one joint required resetting the remainder being OK.

The back of the assembly was then covered with thin cotton cloth glued in place - for strength when being handled and shaped at the next stage.

The rough assembly was then smoothed with a single cut file and trimmed to a close to final shape with a fine razor saw. Figured maple and ebony are brittle woods to work with so a sharp file is required for all shaping work. The file also smoothly cuts the wood so that the maple is not stained by fine ebony dust (as it would be if abrasive sand paper was used).

A central ebony disc - hand filed to fit - has yet to be glued in place. A contrasting brass button will eventually be installed on the disc for attaching a shoulder strap required for supporting the completed instrument when being played.
As an additional decorative feature, the maple pieces are to be 'fluted'. This will also provide additional flexibility of this component for a close fit when finally clamped and glued to the bowl.

The fluting is made with a half round file and finished with a curved cabinet scraper. Guide slots are first made with a round file in each section to prevent the half round file slipping sideways while filing and causing damage.
This component of the clasp is now almost complete and ready for final fitting and gluing to the bowl.

Wonderful little hand fan !
Very tasteful, as usual, John.
Can't wait to see the wood/metal combination.

Robert

Hi Samir - no I do not have a lute of similar dimensions to this so I am looking forward to the final acoustic result as well! The project will provide some additional data concerning air resonance frequency determination.

I also intend to fret the instrument with Pythagorean fret spacings - as the early Tanburs on which the Colascione is thought to have been based would have been fretted (as were the early fretted shorter necked ouds). The Pythogorean spacings are determined by ratios of string division 1:2, 2:3, 3:4 and so on. This means 18 frets to the octave (compared to 12 for the European equal temperament fretting) - additional double frets being at the 1st , 3rd, 6th, 8th, 10th and 11th positions. The long neck allows sufficient space between the double frets at these positions (about 0.6 cm to 1 cm). However, more on that later.

For those interested in the air resonance calculation see the attached sheet. This assumes that the inner area of the soundhole (diameter 0.67D) that I call the 'Dead Zone' has minimal participation in the resonant air flow through a sound hole - confirmed by my recent resonance chamber trials reported recently on the Forum.

http://www.mikeouds.com/messageboard/viewthread.php?tid=14874

Unfortunately, all of the images in this linked topic appear to have been deleted!! However, the attached image shows the air resonance calculation.

The remaining wood/metal interfaces have now been epoxy glued to the bowl and levelled - these are two short liners that the brace ends will be glued to and a maple plate glued to the neck joint position to cover the ends of the metal ribs. The liners will stiffen further the area in which the sound hole is located.
A decorative metal collar has also been glued to the bowl at the neck block position as additional reinforcement of the ribs. All that remains is to finish and clean up the wooden components.

The neck and peg box have been drawn full size and will be made from solid maple. The neck joint will be slightly narrower than on the Dean Castle instrument.

I have a number of sound board blanks in stock glued up and ready for finishing. The smallest of these is a two piece rough sawn spruce blank. Nothing special but it has a 'ring' to it when tapped that sounds promising. The wood was cut from a log years ago on a large commercial, power feed band saw with a 6 inch wide blade so the saw marks are quite deep. The first task then is to hand plane the saw marks out. The sound board will then be reassessed for suitability.

The neck and peg box proportions have been determined from full size drawings and a template for the peg box has been made from card. For ease of working/handling and economy of material the peg box will be made separate from the neck and the two parts joined together with a glued scarf joint. The original had neck and peg box made in one piece.
No CAD (Computer Aided Design) drawing here!

The peg box is similar to that of a violin as found on original colascioni. To keep things as simple as possible and avoid fancy, time consuming carving, the head of the peg box will be left with a plain flat 'scroll' to which some decorative embossed detail will be added.

The neck and pegbox will be made from Sycamore (a kind of soft Maple) as I have several sawn planks of this wood purchased from a wood yard 40 years ago as old air dried surplus stock. The planks were black though exposure to the air so goodness knows how long they had been in store before I bought them - several decades no doubt - so the wood should be pretty stable by now.
Rough blanks for the neck and pegbox have been cut and are final drying in a warm kitchen at low Relative Humidity.
There is some organic stain in the wood (due to the high sugar content of the wood prior to air drying) - typical with this species of wood. The stain does not affect wood strength and is otherwise of no consequence as the neck and pegbox will be stained black when completed.

The neck joint is currently being fitted using the drawing board as an accurate layout surface. The neck joint is to be vertical - as on an oud - not sloping as on a lute as there is plenty of width available at the neck joint. The neck joint will be reinforced with a screw through the neck block.

The Dean Castle colascione is not perfectly symmetrical the neck being offset to the bass side, the grain of the sound board wood sloping towards the treble side and the joint of the two piece sound board being made well over on the treble side. See my attached sketch made when the instrument was examined 35 years ago.
My project colascione will not replicate this asymmetry.

Now that the neck joint has been made, the neck blank must be temporarily attached to the neck block in order to layout the neck geometry and adjust neck alignment. The neck has, therefore, been attached with a long wood screw passing through a hole drilled in the neck block. This hole was drilled by hand and rises at a slight angle to the surface of the neck joint towards the fingerboard surface. For everything to remain in alignment after the screw has been tightened a pilot hole at exactly the same angle as the screw hole in the neck block must be drilled in the neck blank.
This was achieved by first making a guide hole for the drill in the neck blank with a nail of the same diameter as the screw hole. The bowl was placed and held in correct alignment with the neck blank and the nail - guided by the screw hole in the neck block - was driven a short distance (about a cm or so) into the neck blank with a hammer. The resulting short hole in the end of the neck blank was then used to guide a drill bit of the same diameter as the nail to lengthen this pilot hole for the screw.
For this operation a standard wire nail had to be modified by filing the pointed end into a flat surface - in effect making the nail into a punch. Otherwise the pointed end of the nail - acting like a wedge - would have followed the wood grain and thrown the guide hole out of alignment.

So far so good. Now to temporarily assemble the neck blank to the bowl.

With the screw fully tightened the neck joint surfaces are a perfect fit so work can proceed with establishing the final centre line of the neck in relation to the bowl and to check that the upper surface of the neck blank is in the same plane as the sound board. As it happens the final centre line is offset by about 4mm from the centreline of the blank at the nut position. No problem as plenty of extra material has been allowed in the oversized blank.
The plane of the neck upper surface - checked with a metal straight edge - is in perfect alignment with the sound board joint surface.

As it is difficult to assess how much 'pull up' of the neck under full string tension - if any - there will be, I will probably plane back the finger board joint surface a few mm and make the fingerboard correspondingly thicker at the nut end. This will allow for some action adjustment (by planing back the fingerboard) in future without having to reset the neck.

If the neck is to be glued to the bowl with hot hide glue then the screw will be replaced with a nail that may be driven quickly into position with a few taps of a hammer before the glue has had time to gel (a second or two). This is the traditional method used by European luthiers, the nail (or nails) providing proper alignment and clamping force as well as some reinforcement of the neck joint.
On the other hand, if a screw is to be used a slower setting synthetic glue - such as PVF or epoxy must be employed. I am tempted to use the latter adhesive for convenience given the good alignment of the neck at this stage. Should this be the decision, the screw will be waxed before assembly so that it may be easily removed at a later date allowing the neck to be cut off with a saw should any neck reset work be necessary.

Lots of waste material now to be removed from the neck blank!

For ease of handling the peg box will be made separately from the neck (rather than in one piece with the neck).

The sides of the peg box taper from nut to 'scroll' so the first step is to drill the three pilot holes for the pegs through the parallel sided blank to ensure that the pegs when fitted run 'square' to the peg box.

The sides of the blank are then cut and planed smooth to the required taper.

Finally the profile of the peg box is laid out on the tapered blank, cut out and shaped approximately to size with a coping saw and wood rasp. The cavity of the peg box will next be carved out before the peg box is finished to size.

Before cutting the pegbox cavity, the three peg holes have been cut to size with a peg reamer. This provides full peg box width guidance for the reamer. The peg arrangement - unlike the Dean Castle model - is to be two pegs on the bass side and one on the treble side

The first step in cutting the pegbox cavity is to drill out as much waste material as possible. The cavity is then carved out close to finished size with chisels. As on the Dean Castle colascione the cavity is wider at the top of the pegbox and tapers down to a width of about 5 mm at the bottom.

The neck blank has now been trimmed of most of the waste material and is being allowed to season further in a warm dry place before being finishing to size. This will allow any hidden stresses to be dispersed - stresses that might otherwise cause deformation of the completed neck.

Peg box meets neck!

The peg box has been glued to the neck blank with a simple scarf joint. A wooden dowel will be added later for additional strength. The peg box and neck will now be carved and finished as one piece.

I do not make violins so this violin type carved peg box is a first for me. The decorative 'scroll' will be kept plain and simple to save time.

The sound board has been planed and thicknessed - measuring about 2.5+ mm over the neck block area reducing to about 2 mm at the sound board edges. The sound board edges may be later cut for a half depth binding - as on the Dean Castle model. The surface will be hand scraped to final finish after the sound hole has been cut and prior to bracing.

The sound hole will be open as on a guitar so that experiments with different diameters may be carried out. Later, a fancy parchment rosette may be added similar to that on the Dean Castle colascione.

I cut open guitar sound holes - for speed, accuracy and convenience - with a router that has a baseplate modified with a series of radial placed holes at different radii from the cutter bit. The router then spins around a nail to cut the required diameter.

The sound board blank is first firmly clamped to a flat piece of MDF board and a standard nail of appropriate diameter is hammered vertically through the sound hole centre in the blank into the board underneath. The nail is then cut off to a short length (about 5 mm or so). The nail is then positioned into the appropriate hole in the base plate to cut the required diameter. Needless to say, care must be taken to check (and double check) that the set up is correct before starting up the router!
For this project I used a solid carbide router bit 3 mm in diameter set to cut a slightly oversize sound hole diameter of 8.4 cm (compared to 7.9 cm calculated). This will give some scope for adjustment of sound hole diameter later. The router bit is set to a depth that cuts through the full sound board thickness and partly into the MDF board underneath.

So far so good. A nice clean vertical circular cut of the required diameter.

This method can, of course, also apply to the cutting of oud circular sound holes.

The X-ray image of the Germanisches National museum colascione previously posted show a guitar like bracing

https://www.europeana.eu/en/item/09102/_GNM_662343

i.e. relatively wide braces on each side of the sound hole with their ends set into shallow supporting pockets cut into the interior rib liners. As wooden liners are a necessary part of the metal bowl construction I am following a similar design here. The brace ends must fit precisely without forcing or 'springing' the ribs of the bowl

The plan - once the braces have been fitted precisely into the pockets - is to temporarily clamp the braces to the sound board with clamps set through the sound hole. The sound board will then be removed with the braces clamped in position and the brace locations precisely reference marked. The clamps will then be removed and the braces glued to the sound board where marked. If all goes well the brace ends should then fit exactly into their respective pockets when the sound board comes to be glued in place. We will see!

The inside edge of the sound hole is reinforced with full depth black-white-black purfling made by 'sandwiching' plain maple veneer between maple veneer stained black. The glued veneers - with non-stick oven paper on either side - were taped to a cardboard tube of about the same diameter as the sound hole with the grain of the veneer running parallel to the axis of the tube. No hot bending of purfling made this way is required. The pre-formed purfling was further reinforced with a piece of black fine silk fabric (paper would do just as well) glued on top of the 'sandwich' as a final layer.

Once the glue had cured slices - about 4 mm wide - were cut, freehand, from the 'sandwich' using a fine tooth razor saw - the cardboard tube providing the necessary support during the cutting process. Additional segments were cut for spares or use on another future project.

The segments, with ends trimmed square with a razor blade, were then glued and taped to the inside edge of the sound hole. Four pieces and a bit were required - the last piece being the most difficult to fit precisely.

The excess material was trimmed using a scraper blade so that the purfling was made level with the sound board surface. A properly sharpened scraper blade is the best (perhaps the only) tool for the job as it quickly removes fine shavings from the end grain purfling without causing grain 'tear out'.

The soundhole iner edgehas been completed with a solid, hot bent, ebony strip to protect the vulnerable end grain purfling.

With the neck temporarily screwed to the bowl and alignment checked the finished sound board was placed over the two braces and aligned with the bowl centreline. Two small trigger operated clamps were then arranged - passing through the sound hole- to hold the upper brace in position. The sound board with clamps attached was then lifted from the bowl and the outline ends of the brace marked exactly with several strips of adhesive tape to provide positive, precise registration for the brace when being finally glued into position. This was just a 'dry run' test to check the viability of the method. Seems pretty straight forward! The braces will be glued one at a time to ensure an optimum fit without need for further fine adjustment to the fit of the brace ends. Hopefully this arrangement will ensure fast and perfect registration of the sound board when being glued in place.

The little clamps - made in China - cost less than a dollar each from a local 'Dollar' store. They do not provide a lot of clamping pressure but are fine for this particular application. Clamping pressure is released with the press of a button. The clamps can also be arranged to press in the opposite direction - rather than squeeze - if required.

The first brace has been set up for gluing. The hide glue is to soak in water overnight so this brace will be glued tomorrow.

In the meantime other components are being prepared.

One great thing about this project is that the instrument only has three tuning pegs to make and fit! I have a quantity of lute pegs in stock - rough blanks turned as a batch years ago from Brazilian 'boxwood' or Castello. This is not a true boxwood but is very similar and is often used as a substitute for the real thing. I will use the same wood for the fingerboard.

The peg shank taper is cut with a peg shaver or cutter (a kind of giant pencil sharpener) made using my peg reamer - so ensuring the exact peg shank taper.

My pegs are made in the style of the old lute pegs - the peg heads being simply cut flat with a chisel (not fancy curved as on a violin or on some modern ouds). In keeping with the metal to wood theme of this project I may add a decorative 'silver' ring to each finished peg. More on that later.

The second brace has been glued to the sound board and while the glue is left overnight to cure.

The three pegs have been shaped, fine sanded and burnished.
Each peg measures 75 mm overall in length.

Peg collars and end dots have been added as a decorative feature - made from 1.5 mm diameter soft tin wire (available from hardware stores as lead free solder - it is actually an alloy of 96% pure tin and 4% pure silver). This metal looks like silver but does not tarnish black like silver so tin was often used in the past for inlay work in place of silver for this reason.
Pure tin, of course, is the coating on the tin plate ribs of the project bowl.

The procedure for making and fitting these peg collars is described in an earlier project on this forum - posted here on 1-11-2010.

http://www.mikeouds.com/messageboard/viewthread.php?tid=8488&pa...

With the sound board temporarily taped to the bowl, the bridge blank has been positioned with tape and the string height at the bridge determined using a steel straight edge laid on packing at the nut position (1mm string height above the fingerboard) and 16th fret position (3.5 mm action above the fingerboard). With string height determined the bridge blank was drilled for the three string holes and carved to shape.

In preparation for gluing the bridge, its position on the sound board has been temporarily marked with three layers of adhesive tape - an aid for precise registration, important when working quickly with hot hide glue,

The bridge will now be finished and stained black before gluing. After gluing the bridge in place, ebony 'dots' will be added to each end of the bridge as a plain decorative feature.

The bridge material is European Pear wood cut from a small tree in my neighbours garden many moons ago (with permission!) and air dried in small billets for peg or bridge making. Nice close grained wood for carving and relatively low density.

The completed bridge has been stained black with 'Indian ink' available from any stationary or office supply store. This ink is shellac based so dries quickly and penetrates well to a dense dark black. For convenience in handling the bridge when staining and gluing a wooden 'toothpick' has been pushed into the central string hole.

To glue the bridge strong dry granulated hide glue (Lee Valley cat#56K50.01) has been mixed with about 50% water by volume and left overnight for all water to be absorbed. The glue - in a clean glass jar - has been heated in a pan of simmering (just boiling) water until fluid enough for use (the glue runs off the glue brush in a steady stream). The water bath prevents overheating and so spoiling the glue and its strength.

The bloom strength of the glue is rated at 260g so it is very strong - drying to a glass hardness - but gels quickly so set up must be uncomplicated. The set up was tested with several 'dry' runs to determine the optimum position for the spring clamps so that they do not slip and spoil the job. In fact clamps are not essential as the bridge may be held (with great patience) in place with only finger pressure for a few minutes until the glue sets - I prefer to use clamps particularly at the thin, flexible ends of the bridge to ensure that they lay in contact with the sound board surface. A flat board is also temporarily positioned under the sound board as extra support during the gluing operation.

With the bridge glued in place and glue 'squeeze out' cleaned up with a sharp chisel, the next operation is to glue sound board to bowl. The same batch of glue, slightly diluted, will be used for this operation as high strength is not required or desirable for the soundboard to bowl joint.

With relative humidity in our wood stove heated kitchen at an ideal 50% the sound board has been glued to bowl with hot hide glue. The glue has been diluted a little to extend the time until it gels - tested on a scrap of wood. This allows maximum working time but there is still a need to work quickly.

As counter top working space in the kitchen is restricted the pegbox has been wrapped in protective 'bubble wrap' - the long neck of the colascione presenting some difficulty in handling without risk of knocking breakable stuff off nearby shelving. As it happens all went well without mishap.

Both joint faces were given a coat of glue brushed on and the sound board pressed in place and clamped using strong elastic adhesive tape (3M binding tape from Lee Valley cat#25U03.30) starting with the brace end positions, then the neck block location followed by the remainder of the joint. As it is not possible to complete the procedure before the glue starts to gel it is necessary to go over the entire joint again with a hot iron to seat those few sections that have not closely joined. Those areas are first moistened with a little hot water applied with a small brush to soften the glue before being re-taped - once the glue is seen to remelt with the heat application.


The instrument will be left in a warm place overnight for the glue to fully cure. After removing the tape the joint will be checked again for proper fit and any corrections made (the glue reconstituted with heat and moisture - a benefit of hot hide glue). The sound board edges will then be trimmed to size.

The glue pot goes into the refrigerator to prevent bacterial spoiling and the glue will be used again tomorrow for gluing the fingerboard to neck. Reheating hide glue will cause deterioration of the glue strength but a third reheat is acceptable for this application after which the remaining glue will be thrown out.

The adhesive tape used is made by the 3M company (Scotch 233 brand) and is often used by the luthier fraternity for this application. Other 'Masking' or painter's tapes of this type will also work but this brand is strong and will stretch before breaking so can apply a reasonable clamping force. Another way of clamping is to quickly wrap string (or elastic rubber strip) around the bowl and sound board.
When removing the tapes they should be pulled folded back on themselves to minimise any risk of grain tear out of sound board fibres. Any micro fibres that may be raised by the tape will be removed when the sound board surface is later finished smooth with a scraper blade.

When I attended wood working classes at school over 60 years ago only hot hide glue was used (synthetic glues were then an expensive curiosity). The traditional cast iron glue pot was heated up in the morning and left on for as long as needed. The colour of the glue was dark brown (!) - so was not in optimum condition for strength - but maximum strength is not required when gluing woodworking joints such as dovetails, mortice and tenon etc where the strength is in a properly made accurate joint - the glue just holds everything together. In the class work a lot of glue was used in the course of a day so was constantly being replaced.
The same applies to violins where maximum strength is not necessarily desirable - especially in the gluing of the top and bottom plates that may need to be removed in future for repairs. The brittle nature of the cured glue of correct strength allows the plates to be separated without damage with the insertion of a sharp thin knife blade into the joint.
More critical is the gluing of fixed bridges to lutes, ouds, guitars and the like so I use freshly made glue for that work and reheat the same batch of glue for less critical applications. I am not running a commercial luthier enterprise so the glue pot is usually only in use for half an hour or so in a day. It is then sealed air tight and put in the fridge to keep until next required - which may be a few days later as time permits. I only make enough glue required for the work in hand (small quantities) to avoid waste.
My glue pot is a glass jar with sealed lid (the kind used for jam making) heated in a pan of hot water at just below simmering point. From experience and previous trials with a thermometer, glue temperature is held within a range of 140 to 160°F (60 to 70°C). Above that temperature the glue will burn and spoil.
The dry glue is placed in the glue pot and just covered with water. The glue will absorb the water in a matter of an hour or two but I usually leave it soaking overnight for good measure. When the glue is hot and liquid I will test the gel time on a scrap of wood before use and by rubbing between thumb and finger to test viscosity, 'tackiness' etc. All down to experience.
I do not add dry glue to the heated mix (to be avoided in my opinion) but make the glue viscous enough in the first place to require dilution by adding small amounts of hot water as required.

After about 4 reheats any glue that is left over (small quantity) is thrown away. The remaining glue is removed from the jar by adding hot water to dilute the glue residues. A dash of chlorine water (Javex bleach) is then added, the jar filled with fresh water, sealed and left standing for a few days This kills any remaining organic material that is deposited as a white suspension and is poured down the drain to leave a bacterially clean jar for the next batch of glue.

The neck has been shaped and finished to size ready for staining. I use small bronze spokeshaves for the basic shaping followed by a scraper blade before final sanding smooth.
The shape of the neck profile is determined accurately by sight and 'feel' - I do not fuss around with templates for this class of work.
The little spokeshaves are sold as a set of three by Lee Valley (Cat# 61P10.10) and are comfortable to use.

Continuing the metal/wood theme a small solid brass knob has been fitted to the end of the bowl to serve as a button for a supporting shoulder strap. Again this is an item that I already had in stock and so avoids me having to make one (a wide range of these small knobs are sold by Lee Valley - listed in their Hardware Catalogue).

The neck and peg box have been stained black and given a sealing coat of diluted oil varnish. The bowl has also been given a preliminary protective coat of clear oil varnish. Further varnish coats will be applied so this operation could take some time to complete.

In the meantime the air resonance frequency of the bowl has been measured by tapping the bridge and recording the impulse signal at the sound hole on a Zoom H2 digital recorder. The signal is quite strong - the air pulse being felt by my hand positioned above the sound hole.
Analysing the audio signal using 'Audacity' software, the spectrum analysis shows a pronounced air resonance frequency of 212 Hz. This value is about three semitones higher than calculated - 179 Hz -assuming a sound hole 'dead zone' diameter of 0.67D (see previous post on page 2). It is also a higher value than the second string pitch tuned at g 196 Hz (A440 standard) - tuning G g d' - by nearly 2 semitones.
Had this instrument been a perfect Helmholtz resonator, the calculated air resonance frequency - using the full sound hole area as 'active' - would be 240 Hz or about 3.5 semitones higher than 196Hz.

It will be interesting to see how the acoustic response turns out to be. Cutting a half depth rebate and banding around the edge of the sound board would make the bowl/sound board combination less stiff and so would tend to lower the air resonance frequency. By how much? - hard to say without trying.

Attempts to clear varnish the metal bowl have not been satisfactory so the bowl has been given a black 'Japanned' finish, a traditional coating for tinware - in this case the brushed on matt black enamel will be given a protective overcoat of hard clear varnish.

The nut will be made from cow bone from stock prepared earlier from raw bone obtained from a local butcher. The two contact faces have been squared and made flat on a sanding block. The bone has already been prepared and de-greased but will be further de-greased by immersion for a few days in purified gasoline (the stuff sold for use in camping stoves) - just to be sure. An important step as any residual grease in the bone will eventually leach out into the surrounding wood.

Bone preparation procedure was previously posted here:

http://www.mikeouds.com/messageboard/viewthread.php?tid=10403#pid70...

Varnishing of the metal and wooden parts of the bowl and the neck is now complete but will be left for a few more days in a warm place to harden fully. I have used a 'Spar' oil varnish from a local hardware store. It gives a gloss finish that I don't particularly like but the varnish should be durable enough. The sound board is, of course, to be left unvarnished.

Stain, dust and varnish that has partially plugged the string holes in the bridge has been removed with a bit mounted in a jewellers drill.

The same procedure applies to the peg holes using a peg reamer. The stain in the wood acts as a useful indicator of the correct peg fit that should be tighter at the peg head end of the shank than at the smaller diameter free end. This avoids risk of breaking the peg by twisting if it should stick at the free end of the shank. The peg shank will be left extra long to accommodate any initial wear at the peg box. It remains to drill the string holes in the shanks.

The bone nut blank has been finally de-greased with lacquer thinner available from any hardware store and fitted in place. To ensure precise contact with the wood of the fingerboard and pegbox all varnish and stain has been removed.
The next step will be to finally shape the nut and file and polish the string grooves before fitting the strings. At that point the nut will be held in place with a small spot of fish glue - just so that it does not fall off and get lost at any time.

It will be interesting to see how the instrument stands up to full string tension.

I have re-run the air resonance test and the result of the spectrum analysis shows an air resonance frequency of 200 to 201 Hz - very close to the pitch of the middle string (g 196 Hz). For this second test I made sure that there was no influencing effect from the strings by taking more care to completely damp any string vibration - at the neck joint position and between sound hole and bridge - using cloth strips. The previous test shows some influence of string vibration from an undamped section between the neck joint and bridge location.

This result is about a semitone lower in measured air resonance frequency from the preliminary test on the instrument when tested unstrung and without the ebony 'dots' at the ends of the bridge. The air resonance frequency measured then was 212 Hz.

For this tuning (G g d' at A440 standard pitch) an air resonance pitch of about a semitone or two lower should provide optimum reinforcement of bass response. This might be achieved by reducing the diameter of the sound hole slightly or by making the sound board more flexible by thinning around the edges (or by installing a 1/2 depth binding) - modifications that will be tested in future.

Note that this instrument because of its stiff construction around the sound hole area, stiffer sound board and relatively high sound hole placement, behaves a bit more like a true Helmholtz resonator than an oud or lute.
For purposes of calculating the air resonance frequency - the central 'dead zone' diameter of the colascione sound hole - based upon these measured results - is about 0.56D rather than about 0.67D as it would be in the case of a single sound hole oud or lute.
For a true, perfectly rigid Helmholtz resonator with centrally positioned sound hole the whole area of the sound hole diameter D is used to compute the air resonance frequency i.e. there is no central 'dead zone' where little air flux takes place across the sound hole area.

At this stage no changes or alterations will be made to the instrument set up and it is time to consider how the colascione should be fretted.

Before fitting the frets the sound board has been further cleaned up using a cabinet scraper blade to remove a few fine shavings. A 'before and after' resonance test showed a drop in measured air resonance frequency of 2 Hz i.e. from 201 Hz to 199 Hz at an ambient temperature of 15°C. At this frequency range the human ear might just detect a drop of 2 Hz. Not much but I think that this will explain the difference in the measured air resonance frequency when the instrument was first completed (212 Hz) and now (201 Hz) as the sound board was finished to be thinner around the edges than in the centre - a difference of about 0.5 mm - except in the area between the bridge and the bottom of the bowl where the sound board has been left full thickness of about 2.5 - 3 mm. This thinning made the sound board more flexible and so lowered the air resonance frequency as should be expected - all else being equal. ( the trapped air inside the bowl acts like a cushion or spring so any increased flexibility of the walls of the resonance chamber - i.e. the bowl/sound board structure - will soften the spring effect of the trapped air and so lower the air resonant frequency).

In this case the sound board - small in area and relatively thick compared to an oud or lute - has no bracing below the very stiff upper section where the sound hole is located. So one might expect removal of even a small amount of material from the vibrating area to have some reasonably significant effect. This effect will be further tested later when the sound board edge is to be rebated and finished for a half depth binding so further reducing the sound board stiffness around the edges.
In the case of an oud or lute the same effect would be achieved by reducing the stiffness of the multiple sound board braces - a more complex procedure to control and predict no doubt.

For information the attached Audacity spectrum analysis is attached to compare with the graph previously posted.

As the air resonance frequency is about where it should be, it has been decided at this stage - and before fitting the frets - to rebate the sound board edge for a half depth binding mainly to assess the effect, if of any significance, on lowering the air resonance frequency. The frequency should be lowered somewhat.

I have also added my maker's brand to the sound board area over the neck block - a lute maker's tradition. The brand was made from sheet brass high temperature brazed together, filed to shape and fitted to a wooden handle. In use the brand is heated to a temperature high enough to scorch the wood using a propane flame.

The rebate for the half binding is cut with two tools - a purfling cutter to scribe the inner edge of the rebate and a special plane to cut the rebate. The rebate width is 4 mm. I made both of these tools from brass - as reported a while back on this forum.
Once the rebate has been cut and finished the air resonance frequency will be measured again to assess the effect before fitting and gluing the binding/purfling.

In addition to the half depth binding ebony finger board 'points' will be added to reinforce the bottom edges of the fingerboard - as found on the Dean Castle colascione. The points extend to the front edge of the neck block. A metal template will be used for marking out the points on ebony prior to shaping.

The half depth rebate has been finished to about 1mm depth with a low cost nail file or 'emery board'. The rebate where it meets the points must be cut with a chisel as the rebate plane cannot get in close enough.

With the rebate finished the air resonance frequency has again been tested and measured as 195 Hz - a drop of 6Hz from 201 Hz. This is only about half a semitone so not of great significance. No doubt when the half binding is glued in place the air resonance frequency will return to around 200 Hz!

The ebony points must be fitted before the half binding. They have been cut and filed to shape and rebated into the fingerboard/soundboard. The rebate is first outlined with a knife (using the points as a pattern) and then cut out to depth with chisels. The points shown here have not been hammered and glued tightly into place until further fine adjustments have been made to the depth of the rebate. There will also be a strip of ebony inlaid across the top of the points at the end of the fingerboard.

Small 'cranked' chisels are useful to cut out narrow rebates. These are easily made from small diameter high carbon steel rod (broken drill bits, sewing needles etc)- softened by heating to bright red heat in a propane flame and hammered to shape. Then further filed to shape after cooling. The chisel edge is re-hardened by heating to a dull red colour and then dropping it to cool rapidly into a can of old engine oil (or just stick it into a potato!). The hardened cutting edge is then sharpened and honed in the usual way.

With the inlaid ebony 'points' completed and the half depth rebate around the edge of the sound board finished the half depth binding has been made up and glued in place ready for scraping down level with the sound board surface.

The binding is the same as that around the sound hole edge with black-white-black purfling and solid ebony outer edge. The purfling has been made by gluing dyed maple veneer together (like a plywood sheet) from which strips are then cut with a saw. The saw marks are removed and the strips brought to the required thickness by drawing each strip though a block of wood in which slots of varying depth have been cut with a router. A block plane held stationary at an angle over the strip does the cutting operation.

The tightly curved purfling around the bottom edge of the sound board was made the same way as that of the sound hole purfling - preformed on a mold. The disadvantage is that the colour of the end grain does not exactly match that of purfling cut from longitudinal grain veneer. I shall be varnishing the binding so the colour difference may not be so distinct when finished.

The ebony outer edging has been hot bent to fit. The whole binding assembly has been made in pieces (rather than one or two continuous strips) for convenience in handling and economy of material. For convenience of handling I have used PVA carpenters glue to secure the binding - the sections being clamped tightly in position with adhesive tape.

All the binding strips have now been glued in place ready for scraping down to sound board thickness with a scraper blade. To prevent damage to the sound board surface, the corner of the scraper blade has been covered with adhesive tape.

I expect to finish the edge binding tomorrow so will then again measure the air resonance frequency to see if there are any changes resulting from adding the half depth binding.

Note that half depth binding is a style of sound board edge reinforcement found on surviving lutes of the 17th/18th C as well as on some old ouds. It is also found on the Dean Castle mezzo-colascione.

Thank you Luttgutt!

By planing down the fret board, the action (underside of string to fingerboard surface) is now just over 3.5 mm at the 7th fret position (1/3 string length) at full string tension. This location coincides with the join in the two part fingerboard so has been marked for future convenient reference with a piece of ebony inlay (now nobody can see the joint - more luthier trickery!).

The string action is measured with a simple, easily made tool - a tapered piece of hard wood with the depth (measured with calipers) marked along the length.
At the last fret position (fret #27) the action is 5 mm. I will use 0.58 mm diameter nylon (low cost, ordinary fishing line) for the frets so the action above the frets will be around 3mm at the 7th fret. As fret spacing is quite close in places the frets will be single rather than double tied.

The Pythagorean fret spacings - measured from the nut - have been marked on a strip of wood and transferred to the fingerboard with pencil marks. This is how the 16th C lutenists like Dowland did it and so - no doubt - did the early ud and tunbur players. Total number of frets to start with is 27 - but there is space for more.

Tying nylon frets is hard on the fingers (gut frets would be better but too costly for this project) so a small set of pliers helps a bit in making the frets tight. The fret knots are sealed by melting the cut ends with a small soldering iron and the frets slid into position - the taper of the neck providing added tension.

Tying frets is one of my least favourite luthier jobs so the work will be spread over a couple of days. Seven frets tied - only 20 to go!

Nylon frets require a special kind of knot due to the slippery nature of the material - a knot familiar to fishermen. The attached images should make it clearer than words alone.

A suitable length of line is required that allows sufficient surplus length to obtain a good grip and exert sufficient tension once the knot has been tightened and the fret drawn into position. About 15 cm or so should be adequate for this instrument.
A 'figure 8' knot is first tied at one end and the free end passed under the strings and around the back of the neck to the bass side (the fret knots should always be on the bass side of the neck for right handed players). The free end is then passed first through the underside of the loop at the bottom of the 'figure 8' and then through the underside of the loop at the top of the 'figure 8'.

The knot is then pulled tight and the fret pulled up as tight as possible onto the neck at a position some distance (about 5 cm) above the final location of the fret. For good measure a simple half hitch knot is then tied over the knot and the surplus material cut away to leave two free ends about 3mm in length. The free ends are then melted back to the knot - using a small soldering iron - so sealing the knot against unravelling.

The fret is then slid down the neck to its final position - the taper of the neck adding additional tension to the fret to hold it tight against the fingerboard surface.

Once all of the frets have been tied to the theoretical positions marked on the fingerboard they will require further adjustment to allow for the increased string tension (and hence increased pitch) caused by stopping a string against a fret. The proportional increase in pitch depends upon fret diameter, string diameter, string material, string tension of the open string, vibrating string length (of the stopped string), strength of sounding a string, and string 'action' or clearance above a fret. Final adjustments will be made 'by ear'- a compromise until everything sounds in tune.

My set up for fine tuning of the fret positions is to use a low cost 'lapel' clip on microphone (The Source #2616448) input directly to my PC sound card. This is mounted on the colascione with a simple Z shaped clip cut from tinplate and lined with felt to protect the sound board surface. This little microphone provides a signal strong enough for the purpose.

I am testing instrument tuner software 'AP Tuner' and 'Tune!It' both shareware but free to download and use for a limited time. The latter program is a lot more complex and sophisticated and includes an extensive library of historical temperaments, auto sound card calibrator, 3D spectrum display, wave form graphing, inharmonicity analysis etc. etc. and even a facility for ear training. Accuracy of both programs is 0.1 cent. Screen display images are attached for information.
AP tuner can be used indefinitely without registration whereas Tune!It costs about $10 US for registration after 30 days trial. I am tempted to purchase the Tune!It software if these trials live up to expectations.

With the current stringing - first string 0.37 mm PVF, second Nylon 0.6 mm and third Pyramid wound #1010 - tuned as A2 A3 D4 and G2 G3 D4 - attached for information and comparison are the Audacity frequency spectrum graphs showing the most prominent frequency peaks.

The colascione with either tuning is quite loud and resonant. If anything the G2 G3 D4 tuning sounds a bit 'richer' in tone.

Next to restring the instrument to sound an octave lower in pitch i.e. A1 A2 D3 and G1 G2 D3.

The colascione has been restrung to test tuning an octave lower as A1 A2 D3 and G1 G2 D3.

Strings used are those that I have to hand so not ideal - first string Pyramid 0.63 PVA, second Pyramid wound 1010 and third Pyramid wound 1027. String tensions are A1 2.7 Kg, A2 3.5 Kg. D3 2.9 Kg and G1 2.2 Kg, G2 2.8 Kg and D3 2.9Kg.

The attached spectrum analyses, for information and comparison, show some of the more prominent harmonics with the strings sounded open.

For comparison the two attached sound clips are for open strings for G2 G3 D4 and G1 G2 D3. On balance I prefer the richer more resonant sound of the G1 G2 D3 stringing. Interestingly the fundamental tone G1 is not prominent in the spectrum graph although the bass string sounds loud enough. The top D3 string 'sings' nicely in the upper fret positions.
(Unfortunately the sound files have now been lost)

A preliminary assessment of the variation of air resonance frequency with sound hole area for this instrument was undertaken in two ways:

1) by covering the soundhole with 2 mm thick card and then recording the air resonance signal (generated by tapping the sound board just in front of the bridge with all strings damped) - the card being moved in 5 mm steps until the whole sound hole area was uncovered.

2) by covering the soundhole area with 2 mm thick card squares each with different soundhole diameters and measuring the air resonance signal.

The results - air resonance frequency (obtained from 'Audacity' spectrum analysis) against sound hole area - are plotted on the attached graph for information.
The difference in the curve profiles is primarily due to different sound hole geometries - full circle area compared to segment of a circle area. Changes in air resonance pitch are easily distinguished by ear as soundhole area varies.
The loudest air resonance frequency occurs at the point when the sound hole is uncovered to an open area of about 35 cm² (77% of the full sound hole area of 45.4 cm²). This corresponds to an air resonance frequency of 192 Hz G3 which is also the air resonance frequency of the open sound hole there being about a 6 Hz bandwidth tolerance in the measured frequencies.

Thank you so much for sharing your researches.
You're helping me to understand those kind of things way better.
I'm pretty sure a lot of others too !