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jdowning
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Oddly enough, the on-line chemists generally state that the blue precipitate of copper hydroxide is not only insoluble in water but also will not
dissolve in excess sodium hydroxide. One source, however, adds an exception - "unless the NaOH solution is 'very' concentrated".
I have now prepared a batch of the 'silk reagent' by adding a 40% solution of sodium hydroxide (i.e. 40 grams dissolved in 100 cc water) little by
little to the copper sulphate/glycerol solution until the dense copper hydroxide precipitate first formed is dissolved to a clear bluish/purple
coloured liquid - a rather attractive colour. So presumably a 40% sodium hydroxide aqueous solution (or greater percentage) is the very concentrated
level required to dissolve the copper hydroxide precipitate. Testing the solution with wide range litmus papers indicates the prepared 'silk solvent'
solution to be about pH 13 - so quite caustic and about equivalent to the pH value of the 40% sodium hydroxide solution (for comparison pure water is
about pH 7)
Note that on test, the silk waste did not dissolve in 40% sodium hydroxide solution at room temperature.
The current test is to see how much of the silk waste fabric will dissolve in the solvent. The first batch of 0.5 gram silk waste dissolved in 10 cc
of the solvent in about 30 minutes at room temperature. A further 0.5 grams of silk waste has now been added to the mix. This may be about the maximum
silk to solvent ratio (1:10) for complete dissolution of the silk (as reported by some researchers) - but we will see how it goes.
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jdowning
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Checking through my notes on Japanese silk fishing leader gut mentioned earlier in this thread I find the following comment -
" the Japanese 'gut' is made from spun silk covered with a coating of dissolved liquid silk mixed with several chemicals - or bonded with gelatin".
Unfortunately I did not note the source so will have to keep searching to try to find it again but it likely gives no further information about the
dissolved silk. The gelatin or glue binder is presumably similar to the 'conventional' agar agar (seaweed gelatin) binder previously noted in this
thread?
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jdowning
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While the waste silk is being dissolved in the 'Copper Hydroxide' solvent - thinking ahead a bit.
The dissolved silk solution will be strongly alkaline so cannot be just applied to a silk string without risk of the string being also dissolved or at
least weakened over time (?).
To neutralise the alkaline solution to a point where it will not attack the silk fibroin of the string itself, acid must be added to the solution. As
I am only experimenting with chemicals that anyone can purchase 'off the shelf' from local stores the chosen acid is household strength vinegar (5%
strength Acetic Acid).
The acid was added - little by little - to a small sample of the solvent used for preliminary tests to dissolve the waste silk (so contained dissolved
silk). As the acid was added, the solvent changed colour from deep purple to light blue and then began to 'fizz' or effervesce as bubbles of a gas
were given off. Further addition of acid resulted in eventual ceasing of the gas emmission and sudden clarification of the solution. At this point the
solution tested around pH 7 or slightly less (acidic) so is considered to be neutral. The safe range for fibroin is around pH 4 to pH 7.5 (see page 4
of this thread)
Acid + Alkali = Salt + Water (as I remember it). In this case presumably the salt (in solution) is a complex of copper acetate (from the copper
hydroxide portion) and Sodium Acetate (or Ethanoate) from the excess sodium hyroxide portion? Presumably the gas is Carbon Dioxide?
For information, the attached images show the dissolved silk solution before and after adding the acid. Image A is the neutralised dissolved silk
solution and image B - for comparison - is a neutralised sample of the Copper Hydroxide solvent, pale blue and perfectly clear.
Note that the colour of the neutralised dissolved silk sample is close to that of the Japanese silk fishing 'gut' samples previously posted.
[file]27035[/file] [file]27037[/file]
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jdowning
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Another solvent for Bombyx Mori cultivated silk fibroin is that described by researcher Akiyoshi Ajisawa
https://www.jstage.jst.go.jp/article/kontyushigen1930/67/2/67_2_91/_...
The solvent is made from a solution of Calcium Chloride to which Ethanol (Ethyl Alcohol - the stuff in alcoholic beverages) has been added - the
alcohol reported to greatly increasing the solubility of the silk fibroin. Calcium Chloride is readily available as a chemical used to adjust calcium
levels in swimming pools. Pure Ethyl alcohol is less readily available and costly but is otherwise readily available as a solution in water in
alcoholic drinks such as Vodka and Gin.
Chemists give their chemical mixtures in molecular proportions or moles. In this case the optimum proportion of the silk solvent is given as a molar
ratio of 1:2:8 (i.e. calcium chloride: ethanol: water). Expressed as weight (or rather mass) proportions, the ratio becomes 111: 92: 114 grams
(calcium chloride: ethanol: water).
Vodka as a drink is sold locally as a 40% ethanol/water by volume solution. If I have done my sums correctly (as a non chemist - so great margin for
error!) - a mixture of 46 grams of Calcium Chloride dissolved in 100 cc Vodka (don't want to waste too much of the stuff on experiments!) should give
a solution close to the optimum proportions required for the Ajisawa silk solvent (a bit less ethanol at 31.6 grams compared to the ideal 38.3
grams).
At room temperature the dissolution of degummed silk is reported to be very slow in this solvent. However at 60°C the dissolution is reported as
being complete within an hour.
Unfortunately, I had no success in trying to dissolve degummed Bombyx Mori silk using this solvent. Perhaps my calculations were in error or perhaps
the proportion of ethanol in the mixture is more critical than first thought. I did also try using methylated ethanol (ie 'methylated spirit' or
ethanol poisoned with wood alcohol to discourage consumption of the stuff) in the required proportions without success.
Note that this solvent is reported to dissolve only degummed Bombyx Mori cultivated silk - not species of wild silk fibroin - on which it is reported
to have little effect.
(see research report "Dissolution of 'Philosamia ricini' Silk Film: Properties and Functions in Different Solutions" by Y. Srisuwan and P.
Srihanam)
http://scialert.net/qredirect.php?doi=jas.2009.978.982&linkid=p...
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jdowning
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I was able to dissolve 0.6 grams of silk fabric waste in 10 cc of the prepared 'copper hydroxide' solvent previously reported. However, to neutralise
the solution required the addition of about 50 cc of 5% Acetic Acid - making a dilute solution, probably too 'weak' to be useful for string making as
it stands.
Perhaps the solution might be concentrated by heating it to drive off the water content - but this approach has yet to be tested.
To short circuit the path in making silk solution from scratch, I have purchased some ready made cosmetic grade silk fibroin powder for further
experiments. This is the finest grade of powder (Silk Amino Acid) sold by the New Directions Aromatics Inc. company and is soluble in water - although
the degree of solubility has yet to be established.
The powder costs just under $15 for 100 grams - more than enough for initial experimentation. The powder is triple wrapped in sealed plastic bags and
securely packaged in a padded cardboard box for delivery by courier delivered within 7 days of placing the order. Included was even a 'thank you' card
from the company - now that is good customer service!
Some initial testing with small quantites of powder confirmed that the powder could be made into a creamy paste or a solution in water. The powder
dissolved more effectively in Vodka (40% Ethyl Alcohol and water by volume).
The powder has a 'peppery' aromatic smell and in solution is a clear pale yellow in colour.
So - at this point I am not sure if the use of silk fibroin powder will successfully lead anywhere positive in this silk string making investigation -
but no harm in trying.
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jdowning
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I have just come across another snippet of information that may (or may not) be of some significance in the quest for an historical binder for
workable silk strings.
Earlier in this thread forum member danyel suggested that isinglass (a pure gelatin from the sturgeon (and other species of fish) swim bladders rather
than gum arabic) was the binder component given in the Kanz at-Tuhaf commentary on silk string making.
More recently (page 8 of this thread) the method used by the Japanese for making 'monofilament' silk fishing leaders was discussed as a possible
application for silk instrument strings. The binder for these strings - as mentioned by Humphries - was likely a mixture of animal glue and a seaweed
derived gelatin known as 'agar' (or 'agar-agar').
Interestingly my copy of 'Thorpe's Dictionary of Applied Chemistry' - a wonderful but now relatively out dated (4th edition, 1937) encyclopaedia -
under the entry 'Agar- Agar' (Vol 1, page 162) - describes the material as "Bengal or Japanese Isinglass" and " It is employed as a 'size' (diluted
animal glue) substitute - its gelatinising power claimed to be greater than that of gelatin".
It is also used as a size for silk and other fabrics to add gloss as well as a glue (or gum) - so sounds promising as a poterntial binder for silk
strings.
Agar is readily available as a health food additive so a sample quantity must now be obtained for testing! Costs around $7 for 50 grams in powder
form.
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jdowning
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The sample of Agar powder has finally arrived - so investigation of a Japanese style silk string binder can now proceed.
Agar is an interesting material with a number of applications - including a food thickening agent (a vegetable substitute for animal gelatin) and glue
additive. Agar is considered to be a vegetable gum (like, for example, Gum Arabic). It is compatible with proteins so presumably will combine with the
sericin in raw silk filament.
Agar is made from a variety of red seaweed that occurs worldwide - although the the bulk of Agar on the market is of Japanese origin. The properties
of Agar vary somewhat according to the strain of sea weed from which it is extracted. However its unique property is that it forms a firm gel at low
concentrations (0.5% to 8% by weight) in water dissolving in the water at boiling temperature (100°C). On cooling the mixture forms a gel at around
30°C to 40°C. However, unlike animal gelatins, Agar must be re heated to about 100°C before melting to a liquid. This melting/gelling cycle can be
repeated.
The sample available for testing is food grade sold as a 100% pure "Vegetarian Substitute for Gelatin" - a fine cream coloured, odourless powder.
As a preliminary test 1 gram of the powder was dissolved by heating to boiling point in 100 cc of water (i.e. 100 grams). The sample was heated on a
water bath so its maximum temperature in practice was around 90°C. On cooling the fluid started to gel at around 35 °C and became a soft jelly at
room temperature (21.5°C). On reheating on the water bath, the gel became liquid again at about 80°C.
It is assumed that increasing the Agar concentration will increase the gel strength and firmness - but this has yet to be confirmed. Note that an 8%
concentration is used for making dental impressions for casting - so the gel must be quite hard yet still flexible at this concentration.
The concentration of Agar added to a glue or gum binder (to make it more flexible) has yet to be determined. Note that Agar is apparently used as a
component of glue used for manufacturing plywood. Also it has more recently been mixed with UV hardening epoxy glue - as an adhesive used for
laminating flexible LCD touch screens for computers.
[file]27261[/file]
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jdowning
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As the initial trial using a water bath failed to heat the Agar to boiling point, the gel was remelted and poured into a muffin pan placed directly
on a stove hot plate. This brought the Agar to a simmering boil (measured at 100°C) where it was left boiling for 5 minutes before allowing to
cool.
At around 40°C the surface of the Agar fluid started to gel and by about 35°C the gel had become firm enough so that the pan could be turned on its
side.
At room temperature the gel felt like a firm soft rubber on the surface but it was possible with increased pressure to penetrate the gel with a
fingertip (see the hole in the centre in the attached image). The interior of the gel at this concentration was found to be moist with water present.
This would likely not present much of a problem when the Agar gel is mixed with animal glue to modify its elasticity but that will have to be tested.
A second test will be undertaken at an Agar concentration of 8% (by adding another 7 grams of Agar powder to the 1% stuff just tested and bringing
everything to a boil). By all acounts this should produce a very firm gel - but we will see.
It will be interesting to see how well the Agar might consolidate with silk sericin. It is difficult to degum silk completely as there is always some
residual sericin left combined at a molecular level with the silk filament - so the hope is that with even degummed silk the Agar will 'stick' well as
a binder component.
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jdowning
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Two more concentrations of Agar gel have been prepared - one at 4% by weight and the other 8% by weight - just for experience. Both samples were again
heated on a stove hot plate stirring as the temperature increased.
The 8% solution became a rather stiff glutinous bubbling mass with temperature not exceeding about 85°C.
The 4% solution was a little more fluid but still quite viscous - maximum temperature on heating did not exceed about 95°C.
On cooling both samples gelled at around 37°C. At room temperature the 8% solution had formed a firm but flexible rubber like gel that could not be
penetrated with finger pressure.
The 4% solution formed a stiff gel that could just be penetrated with considerable finger pressure.
Both gels - although firm - could be readily cut or broken into pieces.
At these concentrations the Agar was not fluid enough at maximum temperature so would be unlikely to penetrate the fibres of a tightly twisted silk
string.
The workable concentrations of Agar would therefore fall in the range of 1% to 4% - say a maximum 2%? As the firm gels are easily cut this may confirm
the need to mix the Agar gels with stronger animal glues to form a strong yet flexible string binder.
Humphries (previously posted) states that the Japanese silk string binders were a mixture of animal glue and seaweed derived gelatin (Agar?) - but
does not give information about the animal glue used or the proportions of glue to gelatin.
Animal glues such as hot hide glue deteriorate in strength at temperatures above 60°C so the Agar gel would first have to be melted (at about 80°C)
and then added in fluid state to the hot glue and stirred in.
Agar gel can be reconstituted from a higher to lower concentration by adding water to the gel and reheating to boiling point so the samples already
prepared can be used to determine the optimum concentration for adding to hide glue to obtain a strong yet flexible adhesive as a silk string
binder.
Presumably the gel concentration can also be increased by boiling a weaker solution to reduce water content?
More experimental work yet to follow!
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jdowning
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For a futher test of the adhesive and penetration properties of the Agar gels, the 1% and 4% gels were reheated until liquid and then brushed hot onto
two layers of fine cotton fabric to glue them together. The fabric was allowed to dry (it took several hours in each case).
The dried samples of fabric were stiff yet perfectly flexible (like 'starched' fabric. Not surprisingly starch paste being a gum equivalent like
Agar). The 1% sample being more fluid worked best at penetrating the fabric- the 4% sample was very viscous when melted and tended to gel on the
surface of the fabric when applied.
Trying to peel the two glued fabric layers apart - the 1 % gel showed stronger adhesion than the 4% gel. Adhesion was not as strong as would be the
case with hot hide glue - but lacked the hard brittleness inherent in dried hide glue.
This being the case it might be worthwhile first testing the Agar gel alone as a silk string binder - combined only with the residual (and brittle)
sericin coating on the silk filament.
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narciso
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Agar seems to be a weaker but elastically more supple binding agent than animal glue?
So is the idea that one can create an optimal string binding agent by mixing the two- perhaps a bit like mixing chalk and soap to optimize peg
lubrication?
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jdowning
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That is the general idea narciso.
As Alexander Rakov found when using the natural sericin gum that coats raw silk filaments as a binder, the resulting string is stiff (sericin is hard
and brittle when dry). His solution was to condition a string to make it flexible by winding the string around a wooden dowel to uniformly crack the
sericin. I had the same problem when trying Gum Arabic and hide glue as binders and used the same 'conditioning' technique (see page 2 of this thread)
- however I have never felt that 'conditioning' was the way to go - hence my preliminary trials with hide glue modified to make it elastic reported
earlier in this thread.
The Ancient Chinese made their strings (for the qin) using the natural sericin and other additions for their binder. One addition was starch (Rice or
wheat flour) that may have added flexibility just as I am hoping that Agar will. The Japanese appear to have used Agar together with animal glue for a
binder resulting in a smooth flexible 'monofilament' (in appearance) type string. Note that the old Chinese silk strings for the qin were all of roped
construction - three or four strand - so any brittleness of the binder may have been less of a concern due to the high flexibility of the roped
construction. The open strings were also much longer than oud strings.
The primary interest here is to investigate the potential workable tonal range of simply twisted strings (i.e. without roped construction). I would
expect the range to easily cover four courses (as the 10th C ouds were strung - tuned a fourth apart) and might even go down to six courses with high
twist construction.
The trick now will be to determine the optimum proportion of Agar gel to glue (be it sericin, hide glue or isinglas etc.) to provide the required
tenacity/flexibility of binder. The first step will be to try Agar alone with raw silk, the twisted silk being boiled (100°C) in the agar solution to
thoroughly saturate the string with binder - followed by trials using Agar/hide glue and Agar/isinglas mixtures.
The method for adding Agar to the glues will be to first liquify the Agar gel (around 80°C) allow to cool to around 60°C (still fluid) and then add
the prepared glue gel (or liquid glue at 60°C) to the Agar maintaining the temperature at 60°C for use. It will be of interest to note how the
Agar/glue mixture behaves on cooling/reheating cycles.
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jdowning
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For the first trial using an agar binder with raw silk filament (i.e. with sericin gum coating) a short length (37.5 cm untwisted) of 64 silk
filaments was made up. The bundle was soaked in a hot 2% Agar gel and then twisted on the string making rig with 123 twists and 2.4 Kg loading.
In retrospect the number of twists applied was excessive (3.3 twists per cm untwisted string length) resulting in slight buckling of the string along
its length (i.e. the string filaments were starting to 'corkscrew'). The number of twists per cm should have been around 2.0 to 2.5 twists per cm.
Also the hot Agar began to gel on the twisting rig as it cooled prior to applying the twists. Application of heat with a hot air gun helped to remove
some of the twisting irregularities by remelting the gel but a lower gel concentration would likely have worked better.
Nevertheless the twisted test string measured 0.84 mm diameter and was quite flexible - resembling high twist gut even in this preliminary and rough
experimental attempt. Compare with Aquila HT gut here:
http://www.aquilacorde.com/index.php?option=com_content&view=ar...
Presoaking the filaments prior to twisting may not be the way to go so the next test will be first to twist the raw silk filaments and then soak the
twisted string in hot liquid Agar - at 1% concentration to allow (hopefully) full saturation of the string filaments.
[file]27298[/file] [file]27300[/file]
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jdowning
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Test #2
A 64 filament raw silk bundle was first soaked in hot water (to soften the sericin gum), twisted at 2 twists per cm under a loading of 1.4 Kg and
allowed to dry on the twisting rig. The degree of twist was retained on removal of the string from the rig - cemented by the sericin gum.
The string was then immersed in a boiling solution of 1.3% Agar. Things immediately began to unravel - the string twisting and tangling around itself
- so much of the original twist was lost. Nevertheless the string was then replaced on the rig under a 1.4 Kg load, straightened out, wiped free of
excess Agar gel and allowed to dry.
The resulting string was quite uniform and gut like in appearance and flexible yet 'springy' - diameter 0.82 mm. Easily coiled into a small diameter
loop without damage (the coin in the attached image measures 1.8 cm in diameter).
To test penetration of the binder the string was unravelled with some difficulty indicating full penetration and good adhesion of the Agar/sericin gum
- similar to the Japanese silk string test previously posted.
This test must be repeated due to the handling problems that allowed the test string to unwind and lose much of its initial twist when immersed in the
hot Agar solution (and perhaps facilitated penetration of the liquid Agar?)
So far so good.
[file]27308[/file] [file]27310[/file] [file]27312[/file]
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jdowning
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Test string #2 has further air dried and become quite 'springy' so that it is difficult to make a tight knot in the string without causing fibre
separation.
Gut lute strings in the 16/17th C were preserved in oil (such as almond oil) to keep them flexible and moisture free.
Out of curiosity, test string#2 was rubbed with almond oil and became noticeably more flexible so that it was possible to then easily tie a tight knot
without fibre separation.
This opens the possibility for strings made this way to be also used for tied frets on a lute.
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jdowning
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Curious about the apparent reaction of the Agar soaked test string with Almond oil, a small piece of 1% Agar gel was left, a few days ago, immersed in
Almond oil. Checking today, the Agar gel seems to have been dissolved. Surprised at this result, a second sample of 1% gel has been immersed in almond
oil - just to verify this observation.
Test#2 has been repeated with a 64 filament silk bundle being soaked in a more dilute 1% Agar gel solution (at 100°C) and then immediately twisted on
the test rig. While this approach results in complete Agar saturation of the string, the almost instant gelling of the Agar when the string is being
twisted - due to the viscocity of the gel - results in a non uniform string twist and slight longitudinal buckling that cannot be fully corrected with
further application of heat and increased string loading.
The next trial will be to fully twist a string bundle prior to immersion in the hot Agar solution to determine if the Agar will fully penetrate the
tightly twisted silk fibres and bond them into a coherent 'monofilament' string.
NOTE! Further testing to determine the solubility of 1% Agar gel in Almond oil shows that the gel appears to be insoluble - which negates earlier
observations to the contrary.
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jdowning
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I am told by my supplier that all commercial silk filament and spun thread is degummed - or rather partly degummed, as an additional degumming step is
usually required before the silk can be dyed to remove any residual sericin.
The next trial is to first twist a string and then immerse the string in hot Agar to - hopefully - fully penetrate the string filaments.
The ancient Chinese processed their silk strings in this way. They wound the twisted string on a tube that was then immersed in a glue binder
concoction. However, their strings were all three or four strand ropes - a stable construction that would not unwind in the hot binder.
For a simply twisted string a tube holder can still be used but the string must be constrained at each end to prevent untwisting.
First step is to twist the string bundle to maximum twist (about 40° filament angle. The bundle is first soaked in hot water (to soften any residual
sericin) and then immediately twisted and allowed to dry for a day. On release from the rig the test string retained its twist indicating that there
is still some residual sericin present.
The test string was then mounted on a plastic tube - metal hooks on each end being clipped over two screws to prevent the string unwinding. The string
was left quite loose to take care of any shrinkage of the string when being processed in the hot Agar solution.
For the first test a 64 filament string was immersed in a boiling (100°C) 1.3% Agar solution for 5 minutes then mounted on the rig under a load and
left to dry. This string was very flexible - more like a common string used to tie up packages - and was easily unravelled. There may have been some
degree of penetration of the Agar but not enough to bind the filaments into a coherent 'monofilament' instrument string.
The following test with a freshly twisted 64 filament bundle was to boil the string (at 100°C) in a 1% Agar solution for 30 minutes. The string was
mounted very loosely on the support tube but on removal from the boiling liquid had shrunk in length exerting such force as to pull the mounting
screws sideways. Upon drying the diameter of the string had also shrunk from the anticipated 0.83 mm to 0.78 mm.
The completed string was quite stiff and hard and made a distinct 'cracking' sound when wound around a small diameter wooden dowel to improve
flexibility. Penetration of the binder appears to have been complete.
When silk fabric is washed, the recommended maximum temperature of the water is 80° C to prevent damage to the silk. When degumming silk optimum
temperature is about 90°C. Heat damaged silk shrinks, hardens and loses its elasticity. So this appears to be the problem with this test. Possible
solution? - reduce the temperature of the Agar solution to about 80°C maximum for safety.
The next test will be a repeat but with a 1% Agar solution held at 80°C for 30 minutes.
[file]27384[/file] [file]27386[/file] [file]27388[/file] [file]27390[/file] [file]27392[/file]
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jdowning
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Test #6
A 64 filament bundle soaked in hot water (to soften the residual sericin) and pretwisted to maximum twist and allowed to dry.
Then immersed in hot 1% Agar held at around 80° C (between
75°C min and 85°C max) for 30 minutes. On removal from the hot Agar bath the string had shrunk in length and was tight on the mounting tube.
Mounted on twisting rig under a load of 1.9 Kg. Wiped with hot Agar solution to smooth the surface of the string and allowed to dry for 24 hours.
The resulting string was smooth, well twisted and uniform but again stiff and which audibly 'cracked' when wound around a dowel to make it more
pliable. The Agar binder seems to have penetrated all fibres of the string quite well. The string is flexible enough to be tied into a tight knot but
with some separation of the fibres indicating perhaps that a more cohesive yet flexible binder is required?
So if the soaking temperature at 80°C is not sufficient to cause heat deterioration of the silk filament (fibroin) perhaps the Agar itself is causing
changes by being adsorbed into the filament (Agar being compatible with proteins i.e. both sericin and fibroin)?
So the quest continues with more potential alternatives to consider and test!
What seems to be certain, however, is that there is no way that a binder of any kind - hot or cold - can be hand rubbed into a freshly twisted string
to penetrate all of the fibres as stated in Kanz at-Tuhaf - so a fundamental step in the procedure would appear to be missing in that historical
record. Perhaps wiping a twisted string with binder solution after it had been boiled was just a final procedure to ensure a smooth finish to a
string? The addition of a little essence of Saffron (Kanz at-Tuhaf) may have just been to protect the string against rotting due to bacterial
attack?
[file]27475[/file] [file]27479[/file] [file]27481[/file]
[file]27483[/file]
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jdowning
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This series of tests with Agar is to gain a 'hands on' appreciation of the properties of the binder and its workability.
Test #7
A fresh 64 thread bundle was pretwisted - after moistening with hot water - to the maximum number of twists (for this diameter string) of 2.5 twists
per cm. under a load of 1.9 Kg - and allowed to dry.
The Agar gel was again re-heated to boiling point to liquify it and then allowed to cool to 65°C. The pretwisted test string was mounted loosely on
the tube holder and immersed in the liquid Agar for 60 minutes with the temperature maintained at about 65°C ± 2°C. This temperature was chosen in
the event that animal glue in combination with Agar might be tested as a binder - the limit for animal glue (hide, isinglas etc) being 65°C.
On removal from the hot Agar the string was again found to have shrunk in length. The string was then left to dry under a load of 1.9 Kg. The string
was quite uniform in diameter - 0.83 mm - except at one end where there was some evidence of the string starting to 'corkscrew' (ie the twist limit
had been reached).
The resultant string was again found to be a bit stiff but on winding around a dowel to make it flexible no 'cracking' noise was heard. The Agar
appears to have penetrated the string fibres well enough although the fibres could be more easily separated by twisting the string in reverse
direction than for previous strings #5 and #6 soaked at higher temperatures.
Note that the same mix of Agar gel has been re-used for all of these tests - simply reheating the gel to boiling point to liquify it each time. This
has the advantage also of sterilising the gel. Water had to be added for each test to rplace evaporation losses so the gel concentration at about 1%
is approximate.
The specific gravity of each test string was determined by weighing each sample, measuring diameter and length to calculate volume and calculating the
S.G. which ranged between 1.24 and 1.27 - confirming that the silk thread used for these trials was partially de-gummed. The Agar itself - being
mostly water (SG = 1) - adds nothing the the specific gravity of the completed string.
Each test string sample was then loaded to breaking point to determine the Ultimate Tensile Stress. Load was applied using a spring balance.
Unfortunately with each impact of string breakage, the pointer on the balance moved to a different zero point so the indicated breaking load had to be
estimated each time as there is no reset facility on the balance. So - for what it's worth breaking loads ranged from about 10 Kg to 12 Kg.
Calculated UTS for the test strings then ranged between 0.20 GPa (Giga Pascals) to 0.22 GPa. This compares with average commercial values for Bombyx
Mori silk of 0.5 GPa for raw silk and 0.65 GPa for degummed silk - values, however, that apply to untwisted single silk filament under load.
The lower UTS values for the twisted test strings may have been partially due to heat damage to the silk but probably mostly due to the high twist
that was applied to the test strings - a reason why high twist silk strings (as well as gut) are not suitable for use as treble top strings - they
will just break under tension. Top strings must be of low twist construction.
So if the test string calculated UTS is about right (despite the potential inaccuracy of the measurements) at say 0.21 GPa a top string measuring say
0.45 mm diameter would break at a string tension of 3.3 Kg (in practice a factor of safety of at least 2X (ie breaking load of 6,6 Kg) would be
required to prevent breakage).
Note that the Agar binder likely does not add significant strength to a string except perhaps in the case of strings made from spun rather than
unbroken filament silk.
Clearly there are an infinite number of possible combinations of these variables:
- temperature
- soaking time
- Agar concentration.
- degree of twist
- string diameter
- string loading during twisting and drying
The simplest way to soak a string in liquid Agar is at boiling point (100°C) as this does not require constant measuring and adjustment of
temperature throughout the soaking period. Reducing the soaking time to somewhere between the 5 minutes and 30 minutes already tested (say 15 -20
minutes) might be a good compromise to achieve full Agar penetration without any associated significant heat damage (hardening) of the silk
fibroin?
So next to make a full length 64 bundle, Agar binder string for testing on a lute.
[file]27571[/file] [file]27573[/file] [file]27575[/file] [file]27577[/file]
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narciso
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jdowning, You mention above that you consider agar to be compatible with the proteins sericin and fibroin. Do you mean this only in the sense that it
does no dissolve them? Or do you mean that agar's penetration into the protein matrix is particularly strong ?
Perhaps the strength of capillary force governed penetration for different binding agent candidates could be roughly appraised by measring the
spreading circumference of a controlled drop on silk fabric. Your test for adhesive strength of agar on cotton fabric is along similar lines, but
agar-cotton is essentially a starch-starch interaction surely; as opposed to the starch-protein interaction relevant for agar-silk?
Do you anticipate that a significant additional degree of mechanically forced penetration will occur when you combine the drying process with a
sizing die ? (which I assume you will be doing at a later stage as you aim for uniform diameter)
Your mention of a possible antibacterial agent used by the old masters is intriguing. WOuld this have been added to the melt or rubbed on later after
drying do you think?
Thanks again for this fascinating series of posts
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jdowning
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Thanks for your comments and suggestions narcisco.
I am not sure at present how agar might associate with the proteins sericin and fibroin of silk. Checking out the general properties it is said that
agar is compatible with protein whatever that may mean. The sericin coating of raw silk filament is apparently a four layer substance. The outer layer
being soluble in hot water is easily removed - the last layer being difficult to remove being combined with the fibroin at a molecular level. To
de-gum silk to a level required for dyeing or spinning, chemical additives (such as soap) must be used.
My thought here is that the Agar might be adsorbed by the outer sericin layer when heated to form a strong bond between the string silk filaments -
both sericin and agar being in solution at 100°C. As commercial silk is partially degummed I cannot at present fully test this idea. I am able to
purchase raw silk waste (short lengths) that requires degumming before it can be spun into thread but I do not have a source for raw reeled
(continuous filament) silk that I need.
Not sure if Agar is classified as a starch as you suggest?
As I have some old silk fabric I shall test some samples with Agar to see if there is better adhesion to the silk fibres than with cotton fabric. Silk
fabric is of course de-gummed so this will be an interesting trial.
Note that degummed fibroin will readily absorb not only dye but other chemicals. One that particularly interests me (reported earlier in this thread)
is Tannin (used to cure leather among other things). Tannin can be absorbed to a high degree and adds mass to the fibroin - so is a weighting agent.
Perhaps it will also combine with Agar?
I am not sure if sizing dies will be necessary to create greater uniformity or smoothness than can be obtained by twisting the filaments but I doubt
if use of a sizing die would increase further penetration of a binder other than just being a surface finish procedure. The pratical test for adequate
uniformity will be to try the strings on an instrument.
Agar held at 100°C for a period of time would be sterilised by the heat but for good measure an antibacterial coating rubbed on the surface of a
completed string might be of benefit. Once the Agar has fully dried there should be minimal danger of destructive bacterial attack?
The directive in the 14th C Persian work Kanz at-Tuhaf is that "a paste of moderate consistency of gum and a little essence of Saffron is rubbed on
the strings with a piece of linen until it has penetrated into all the parts ". I know that simply rubbing a binder solution onto a fully twisted
string will result in no more that a superficial surface penetration. As it would be impossible to know if this mixture had fully penetrated into all
the parts of a string (without pulling the completed string apart!) then I take this passage to mean that the mixture is rubbed onto a string so that
the coating is uniform, covering the entire outer surface - i.e. it is the equivalent of a varnish coating that string makers today often apply to
their gut strings for additional protection and durability. I also reckon that the Saffron may impart some antibacterial protection.
Bear in mind though that gut and silk strings have a finite useful shelf life - so will eventually deteriorate on exposure to the atmosphere even if
left unused.
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jdowning
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Following up on the question of whether or not there is some interaction between Agar and Bombyx Mori silk proteins, I ran some quick tests this
afternoon with a silk cocoon - that should be sericin coated raw silk (but may not be as the cocoons are generally purchased by those wishing to dye
them various colours for decorative purposes and so may already be degummed. This will have to be checked out with my supplier) - and with pure
fibroin silk powder.
The cocoon was cut in half to remove the sad remains of the pupa. Two glass containers were heated in a bath of boiling water - one containing water,
the other liquid Agar - with a cocoon half floated in each like little boats. The cocoon halves remained in the fluids for 15 minutes the temperature
maintained between 85°C and 90°C. The cocoon halves were then removed and allowed to dry and will be examined for penetration of the Agar
tomorrow.
The hot Agar solution was then spread on two pieces of silk fabric to test strength of adhesion later once the Agar has fully dried.
A level teaspoonful of pure silk fibroin powder was then added to about 15 cc of the hot Agar solution (still heated on the water bath) and stirred
into the fluid to see if it would dissolve. After a minute or so the mixture suddenly began to bubble, as if boiling, and the powder appeared to
dissolve completely into solution creating an almost transparent golden orange coloured soft gel (gel point temperature about 50°C). The resulting
gel is clearer than 1% Agar gel that is a milky coloured and translucent (or semi-transparent - see attached images).
This is a very interesting result and suggests that hot Agar solution does combine with fibroin.
I shall repeat this test again (reconstituted fibroin powder) using a new, clean glass container (just in case there has been some cross contamination
with chemicals from previous trials). I will also try to dissolve some degummed spun silk thread in the same manner.
To date I have only been able to successfully dissolve silk fibroin in the standard copper hydroxide solution used as a test for Bombyx Mori silk - as
previously reported in this thread.
[file]27621[/file] [file]27623[/file] [file]27625[/file]
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jdowning
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Although the reconstituted silk fibroin powder does not dissolve in cold water further tests show that it readily dissolves in water at boiling point
to produce a clear golden coloured liquid. So the presence of Agar in the solution is not a factor in the dissolution process as previously thought -
although it would seem that the Agar is compatible.
A smear of water/silk fibroin powder solution on a plastic plate was left for the water to evaporate leaving a dry powdery film - presumably of the
reconstituted silk powder.
Further attempts to dissolve degummed spun silk thread in hot 1% Agar solution over time failed. So (perhaps not surprisingly) it can be concluded
that silk fibroin in filament form has different properties from silk powder reconstituted from silk fibroin filament. Still not sure at this point if
silk powder might have a useful application in the string making process. In solution though it has a nice 'saffron gold' colour.
The cocoon halves soaked in hot water and hot 1% Agar upon drying were both so tough that it has been impossible the tear them apart with the fingers.
As far as I can tell the Agar solution has fully penetrated the 'walls' of the cocoon that are about 0.5 mm thick.
Silk fabric pieces saturated with the hot Agar solution - upon drying - showed very little tenacity and were easily peeled apart although the silk
pieces were stiffer than before.
The bundle of degummed spun silk threads - saturated in the hot Agar solution in a further unsuccessful test to dissolve the fibroin - was placed upon
the twisting rig, twisted to a low twist level and allowed to dry under a 1.9Kg load. The string (0.45 mm dia.) failed overnight while drying
suggesting that for strings made from spun silk a stronger binder than Agar is required - at least for the smaller diameter low twist strings. Or,
perhaps only reeled (i.e. continuous rather spun from short lengths) silk filament should be used for the smaller diameter strings where maximum
breaking strength is required.
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jdowning
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Now that it has been found that silk fibroin powder readily dissolves to solution in hot water, a 64 thread silk string test sample has been soaked in
a hot 8% solution of silk fibroin solution prior to being twisted. The immersion was for 30 minutes at 90°C then twisted to maximum twist under a
load of 2.4 Kg. The dried twisted string sample was then immersed in the boiling (100°C) fibroin solution for 15 minutes and then allowed to dry
under a loading of 2.4 Kg.
The resulting dried string sample, measuring 0.81 mm diameter, was quite stiff so was 'relaxed' by winding around a wooden dowel of 1/2 " diameter.
There was no distinct 'cracking' sound as this was done (unlike the hot agar soaked sample previously reported). The relaxed string sample was 'gut
like' flexible yet still springy and could be tied into a tight knot. Compare this to the broken lute string depicted in Holbein's painting the
'Ambassadors', 1533 - National Gallery, London.
So, silk fibroin solution may potentially be another binder for making silk instrument strings.
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jdowning
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The other potential binder for silk strings is isinglas (glue made from fish swim bladders).
Isinglas - like hot hide glue - may be prepared by soaking in water and then heated until liquid before being applied hot.
Like hot hide glue, once prepared this way, it has a limited 'shelf life' and soon subject to decay.
Charles Holtzapffel in book 1 of his five books on 'Turning and Mechanical Manipulation', London, England 1843 describes a very strong glue (or
cement) for ivory work - gluing ivory to ivory - otherwise known as 'Diamond Cement'). This glue was made from isinglas dissolved, not in water, but
diluted spirits of wine (ethyl alcohol) or more usually common gin. The two are mixed together and gently simmered on a boiling water bath for about
an hour until the isinglas has fully dissolved and is ready for use. When cold, the glue is an opaque, milky, hard jelly that does not decompose over
time due to bacterial attack. The glue must be liquified by reheating on a water bath before use.
In the 19th and early 20th C when the general population of Britain and North America/Canada were more self sufficient (out of economic necessity)
than today - there were a number of publications - recipe books containing formulae for making everything of use in the home and industry - including
adhesives for a variety of applications.
For example the 'United States Practical Receipt (sic.) Book', Philadelphia, 1844 gives a formula for making 'Armenian Cement' (aka 'Diamond Cement').
This cement is made from isinglas dissolved in alcohol with the addition of gums - presumably to add more 'body' to the glue and perhaps an anti
bacterial element (gum ammoniac or galbanum?).
The point here is that isinglas is compatible with vegetable gums dissolved in alcohol. Agar is also classified as a vegetable gum and can be
dissolved in alcohol.
So more potential combinations of glue/gum binders (in alcohol) may be possible!
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