jdowning
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Making Imitation Tortoiseshell
In this topic I plan to try to make imitation tortoiseshell in sheet form for instrument applications from casein. No guarantees that the experiments
will succeed but at least it will be an opportunity to test home made casein glue - a type of woodworking glue used by the ancients.
Casein is made from milk protein - it is essentially the first stage in making cheese - i.e. cheese curd. It is made by souring milk with an acid.
After purification the raw casein may be used 'as is' as a form of air drying plastic (that may be further hardened by chemical treatment) or by
treatment with an alkali (the opposite of an acid) to form a liquid that may be used as a strong wood glue or a paint (a.k.a. milk paint).
I shall be using household Vinegar for the souring acid and Borax for the alkali. I have chosen Borax because it makes the casein able to absorb paint
pigment (water and oil based) as well as being a good preservative against bacterial deterioration. (Borax can also be used to make Shellac soluble in
water rather than in the usual alcohol).
All of these materials are readily available from local grocery stores at reasonable cost and are safe to use.
I just had to purchase a packet of skimmed milk powder. This is fat free (important) and has been pasteurised (by law) to destroy any nasty bacteria
that would make it unfit or unsafe for human consumption. This brand has added vitamins that are unlikely to affect the experiments but if all else
fails I can always drink the stuff (i.e. the skimmed milk powder mixed with water - not the casein glue!).
So lets make some Borax-Casein to 'start the ball rolling'
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jdowning
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Step 1 in this project is to make some casein. This stuff may be bought ready made from health food stores but there is no fun in that (famous last
words!).
Starting with fat free skimmed milk powder from the local grocery store. Following the instructions on the packet 50 grams of powder are mixed with
500 ml of water (0.5 litre). The slightly yellow coloured powder appears to dissolve easily with a little stirring. However to make sure that the
powder has fully absorbed the water the mixture was left in the refrigerator for a few hours. The glass mixing bowl was first sterilised with boiling
water and then covered with 'Klingfilm'.
The mixture was then placed in a stainless steel pan put on the stove set at low heat to warm up (the reaction works best when the skimmed milk is
warm). The pan was removed from the heat when the temperature reached 100°F (38°C). Maximum allowable temperature is 110°C - higher than that will
spoil the casein.
Household vinegar was then added little by little with stirring until the milk began to 'curdle' on the surface at which point no more vinegar was
added. (too much vinegar will reduce the yield of casein). I used 15 ml (c.c.) of vinegar.
The solid 'curd' is then strained from the liquid through a piece of cotton cloth and washed clean of vinegar with water. The white solid material
left in the cloth is casein. Not a lot of casein from this batch.
The casein may then be air dried after sterilising by washing with isopropyl alcohol ('rubbing' alcohol) and then stored in a refrigerator.
First time around I have decided to skip this step and move to the next stage of making glue by adding borax to the moist casein. Not sure if this is
the way to proceed however. Tomorrow will tell.
[file]35405[/file] [file]35407[/file] [file]35409[/file] [file]35411[/file] [file]35413[/file]
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jdowning
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The volume of the solid washed casein, after the water has drained away, is only about 10 ml - so not much to work with. The moist casein has the
consistency of a stiff rubbery yoghurt.
A borax saturated solution was made by mixing 16 grams of borax crystals with 125 ml of hot (not boiling) water. Borax will not dissolve in cold
water. To ensure the borax crystals fully dissolved this operation was undertaken with the container placed in a pan of near boiling water until the
crystals had fully dissolved. The borax solution was then left to cool.
An equal volume of the borax solution was then added to the moist casein solid, the mixture stirred and then left for a few hours for the borax to
fully react with and dissolve the casein. This has produced a slightly viscous translucent pale milky coloured liquid.
This casein glue is a bit thinner than anticipated so a better plan in future would be to mix in the borax solution bit by bit until the desired paint
like consistency is achieved. The reaction in each case may take a few hours for the casein to fully dissolve.
The thin casein glue solution (20 ml) will be allowed to dry on a plastic sheet for a few days (water evaporation) in order to assess the
hardness/flexibility of the thin film produced before proceeding further with this experiment.
The ultimate objective is to use the casein-borax glue as a 'glaze' in a 'faux' painting technique using coloured pigments to simulate tortoiseshell
(or any other desired pattern) - the thickness of the film being built up in several layers to provide a 3 dimensional appearance to the (hopefully)
translucent and hard finished product.
A long way to go yet before this objective is achieved!
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jdowning
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The casein-borax solution has been allowed to air dry after pouring a small amount onto a flat sheet of plastic. It has taken a couple of days to dry
to make a thin transparent film about 0.15 mm thick. The dry film is brittle and easily broken by bending.
Due to uneven drying conditions (the side of the film in contact with the plastic dries slower than the side exposed to the air) and shrinkage due to
water evaporation the thin film has not remained flat but has curled up towards the faster drying side.
Allowing the solution to dry 'sandwiched' between two flat sheets of aluminium might result in production of a flat film? A thicker casein-borax
solution might also dry with less distortion.
So far so good.
[file]35446[/file] [file]35448[/file]
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jdowning
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The remainder of this batch of casein-borax solution has been poured into two small makeshift molds folded from aluminium foil - the folded corners
are watertight. The molds measure about 2cm X 4cm X 5mm deep. The heat conducting aluminium foil allows more uniform drying of the solution.
The solids content of the casein- borax solution is quite low so after a few days of air drying the film thickness left in each mold (that was
initially filled with solution to 5 mm deep) is only about 0.25 to 0.3 mm. Note that the solution also dried on the walls of the mold so creating a
stiff surrounding 'flange' that appears to have stabilised the film - preventing the curling observed in the first trial with a plastic mold.
The aluminium molds - being rough and ready - are not flat but the dried film appears to have followed the mold contours without significant
distortion
As before, the dried film is almost fully transparent and brittle. The dried film does not stick to the aluminium so is easily released by unfolding
the mold.
Use of flexible aluminium foil molds may be the way to proceed in production of thicker multilayer films - three or four pourings (at current solution
concentration) - allowing each pouring to dry in the mold - to produce a transparent film about 1mm thick.
To simulate tortoiseshell, the first and second layers, when dry, would be 'faux' painted with acrylic pigment (the difficult artistic bit!).
First trial will be to make a thicker multilayer transparent film in a flat aluminium foil mold of larger dimensions just to see how that works and
then - if successful - to attempt a faux painted version as a second trial.
The same concentration of casein- borax solution will be used for these trials. The possibility of using more concentrated solids solutions for higher
casein yield may be investigated at a later date.
[file]35522[/file] [file]35524[/file]
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jdowning
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For the next series of multi layer trials a small mold - easily made from thin aluminium foil - will be used. The foil is the stuff used in the
kitchen.
In this case, the foil has - for convenience - been wrapped and smoothed over a small flat bottomed container to produce a circular mold of about 4.5
cm in diameter but - of course - a mold might be made in any shape or size.
The mold - after trimming the walls to about 1 cm in depth - is still quite flimsy so has been stuck to a flat metal plate with thin double sided
adhesive tape (so called 'transfer tape' available from Lee Valley). This is to provide additional strength in handling but also to ensure that the
bottom of the mold is flat.
Note that in making this particular mold, gaps have been left between the strips of tape (for no particular reason) - gaps that show though the thin
foil and that will be apparent in the finished casting. So, if desired, any design or signature might be traced into the bottom of the mold with, say,
a ball point pen - impressions that will appear in the transparent castings as a decorative feature.
[file]35692[/file] [file]35694[/file] [file]35696[/file] [file]35698[/file]
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jdowning
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Another batch of casein-borax solution (of the same concentration as before) was prepared this morning. This will be left in a sealed glass container
for 24 hours to ensure a complete reaction between the casein and borax.
The test mold of aluminium foil - 4.5 cm in diameter - will be filled to a depth of 5 mm for each layer, each layer being then allowed to fully dry by
evaporation. The measured volume of casein-borax solution for each layer will be 8 ml. (or 8 c.c. for us old timers). This will take some time to
complete - slowly air drying layer by layer.
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jdowning
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The new batch of casein-borax, after standing at room temperature for 24 hours, had separated into a uniform translucent but cloudy yellowish liquid
over a layer of a gel like material. The two layers were then combined by stirring at a temperature of 140°F (60°C). On cooling to room temperature
the result was a uniform yellowish translucent viscous liquid with no tendency to separate.
The test mold was placed on a level surface - a block of wood levelled with a bubble level and clamped in a vice. The casein-borax liquid was then
made temporarily more fluid (less viscous) by warming the storage jar in a pan of hot tapwater before an 8 ml sample was measured and poured into the
mold to form the first layer. This will now be left to cure and dry at room temperature - which should take about two days or so.
The remainder of the casein-borax goes into the refridgerator to reduce any risk of spoilage. At these temperatures the fluid becomes a stiff gel.
[file]35726[/file]
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jdowning
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After two days, the first layer of casein-borax in the mold has almost completely dried to a transparent layer.
It has been decided to add pigment to try to simulate tortoiseshell patterning during this trial rather than later.
Casein-borax will accommodate both water and oil based pigment - here cheap acrylic water based pigment is being tested. The pigment is diluted with a
little water and dots of the colour placed at random on the surface of the dried first layer. The first colour is a chocolate brown - Burnt Sienna.
This has now been covered with the second layer of casein-borax liquid (a measured 8 ml volume) that will be transparent when dry after a couple of
days - so encasing the pigment between the two layers. When the second layer has dried further pigment (black and orange) will be added at random over
the first pigment pattern. Hopefully this will give a full depth three dimensional effect to the colour pattern.
Apparently the coloured pattern in true tortoiseshell is not sharply defined (as often seen in fake plastic 'tortoiseshell') but is 'blurred' in
outline. This blurring is achieved in 'faux' painting by dabbing the still wet applied colour patches with a dry, soft fine haired brush.
The second colour application will again be covered with a third layer of casein-borax. If there is sufficient casein- borax fluid remaining from this
batch a fourth layer may later be added.
Note that when pouring the syrupy casein-borax fluid into the mold any trapped air bubbles should be moved to the edge of the mold (with a toothpick
or similar tool)
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jdowning
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The second layer has now dried so more patches of coloured pigment have been added to the surface. I do not have any images of real toroiseshell to
copy so the random pattern likely is nothing like tortoiseshell patterning. Never mind - this trial is just to test the principle of layered 'faux'
painting.
Another 8 ml of liquid casein-borax has been poured over the pigmented pattern so will take another 2 or 3 days to dry. I made the mistake of stirring
the warm casein-borax solution before pouring - hence the multitude of fine air bubbles suspended in the viscous fluid. Perhaps they will disappear
once this layer has dried?
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jdowning
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Although the mold and casein-borax fluid layers were each left to dry on a levelled surface, the drying process has been very uneven. This may have
been due to the relatively small surface area of the mold or because I did not wait for each layer to dry completely before applying a second coat of
liquid - preferential surface tension causing migration of the still fluid material away from the already dried layers? Localised separation of the
pigmentation is further evidence of movement of the fluid layers during the drying process.
The attached image shows the top part of the mold with a dried (and cracked - after being bent) layer about 1 mm thick and the lower part only part
dried about 3 mm thick.
Attempts to remove the aluminium foil by scraping were only partly successful over the dried area. Casein-borax - like a paint - can also be a
glue!
An attempt to chemically remove the foil by dissolving in acetic acid failed - the acid was simply absorbed by the casein-borax and turned it into a
firm gel. In retrospect perhaps not so surprising given that the casein was originally formed by the reaction of vinegar on milk protein.
Nevertheless the translucent nature of the hardened and pigmented part of the casting is encouraging.
Another trial is therefore planned , with a mold of larger surface area coated with a wax release agent as a precaution against adhesion of the dry
casein-borax. This time each layer of casein-borax will be allowed to dry completely.
[file]35880[/file] [file]35882[/file] [file]35884[/file]
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jdowning
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The test sample, softened by immersion in acetic acid (vinegar), has been allowed to dry and has returned to a relatively hard solid state.
Before discarding this latest sample, the aluminium foil has been removed mechanically by scraping. The sample was then immersed in water to test its
moisture resistance. However, after only half an hour immersion in water the surface of the sample became 'slimy' and after five hours immersion the
whole sample had turned to a soft rubbery gel and the immersion water had turned cloudy. In this partially dissolved state and as a final test, the
sample was sandwiched between oven paper and heat applied with a household iron on low heat setting. The idea was to test if heat - by baking the
protein - might have a permanent hardening effect. Alas, after a few seconds of heat application and some sizzling noise the sample turned into
something like melted cheese flowing onto my bench where it had to be removed with a spatula.
So the casein-borax as a dried solid is not moisture resistant enough for practical use as a decorative fingerboard material. I suspect that the
commercially available casein based imitation tortoiseshell sheet material has been chemically treated with formadehyde to harden and preserve it
against softening in moist conditions. Formaldehyde is nasty stuff - used by funeral parlours for preserving human remains - but not now generally
available, so this material is not an option.
However, as borax-casein is an emulsifier it means that polymerising oils - such as linseed or tung oils - can be added and mixed in solution so
making the casein-broax binder moisture resistant and suitable for outdoor applications. So this may be the way to go for future trials although the
optimum proportion of oil to casein-borax solution has yet to be established.
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jdowning
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There is a little casein-borax material left over from the last trial - not much, only about 7.5 ml. Nevertheless enough for a small scale preliminary
test to try the waterproofing effect of adding polymerising oil to the casein-borax.
I have some pure tung oil in stock (Lee Valley Co. product) so thought I would try adding that just to see what happens. Pure tung oil is heat treated
to improve drying properties but contains no chemical dryers so is used to finish wooden food containers such as salad bowls.
I have no idea what the ideal proportions of oil to casein-borax of this concentration might be so I have added 25% oil by volume to make 10 ml for
testing. Mixing the two fluids together with a wooden spatula quickly and easily formed a uniform white cream like emulsion that hopefully will turn
transparent on drying? This sample has been placed in a sealed container in a refrigerator until required.
As a quick test the small amount of residue left behind in the mixing vessel and on the tip of the spatula has been thinly spread on a piece of
plastic to air dry - which may take a day or two. Already after an hour or two the emulsion on the wooden spatula has turned transparent (no doubt
partly absorbed into the wood as well?) so that is a promising sign.
[file]36090[/file] [file]36092[/file] [file]36094[/file] [file]36096[/file]
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jdowning
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In order for the small sample to dry it had to be separated from the plasic (to allow air to both sides) and even then has taken days longer than
expected to fully dry. The dried sample is translucent and still brittle but has the addition of the Tung oil made the casein-borax water resistant -
suitable for exterior use according to some guides?
The sample was then dropped into cold water and within seconds started to soften turning opaque white in the process - returning to an emulsified
state perhaps? Anyway conclusive proof that this sample of casein-borax treated with a polymerising oil is not water resistant. I could try
substituting boiled linseed oil (another polymerising oil) for tung oil but doubt if it would be worth the time and effort to try as it most likely
would give a similar result.
Perhaps a simpler procedure for making imitation tortoiseshell in layers with 'faux' painting sandwiched between would be to just use a clear varnish
for casting the layers instead of casein- borax?
For casein to work as a medium I reckon that a commercial treatment with formaldehyde is required - so too dangerous to attempt even if I could get
hold of the stuff.
Ah well it was all worth a try!
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