[Civisover]

Hello, I'm a violin maker, experimenting with varnishes. Propolis, being dissolved in water with NaOH gives a very nice golden-red color(pics 1 and 2). It's not safe to use strongly basic solution for my purposes, because it will still absorb water from the air. But as soon as I neutralize the solution, or try to precipitate it, it changes the color to pale yellow. Two regular ways of preparing a coloring agent in violin making, that I've tried with propolis, are: soaking something colorful in a potassium carbonate, and then add an aluminum potassium sulfate solution to that, the precipitant will be a pigment(pic.3); and the second one is to dissolve a rosin and something colorful in potassium sulfate and then add aluminum chloride, the precipitant will be a colorful rosinate, that can be dissolved in turpentine(pic.4).
So I'll be very grateful if you help me with some questions.
What in propolis reacts with lye and gives it such a nice color? Is there a way to keep this color and make it possible to add it to alcohol varnish?
If I failed to describe something clear enough to understand, please ask. Thank you!

[Borek]

No idea what is present in propolis, but there are plenty of chemicals that change their color following pH changes. Some of them are even used as indicators to check solution pH (phenolphthalein, litmus, methyl orange to name a few). They won't keep their color after the pH changes (as it does during the neutralization of the solution) so I am not at all surprised with your observations.

I know it doesn't push you forward, but perhaps knowing that will save you some frustration during further tests.

[Enthalpy]

That's not the original query, but: what if you use mineral pigments in propolis? Their colour is stable over time  and less sensitive to chemicals, the commercially available offer is huge (I knew one shop in Munich). Maybe a not too volatile thinner added to propolis suffices then? Avoiding ionic compounds should make the varnish more water-repellent.

Also, I've just seen that linseed oil is used in some varnish compositions, so please take care of your health, since linseed oil isn't completely innocuous.

Did you too observe that a violin sounds better before varnishing?

[Civisover]

Thank you for your replies, guys!
Borek, it's interesting, and makes sense, I didin't think about the color change in that way, thank you.

Enthalpy, yeah, I guess, the easies way is to just dissolve propolis in alcohol, and then add some pigments to  get a wanted color. But if I could preserve the 'propolis's in lye color' somehow it could solve it with just one ingredient.

Yes, there are two varnishes mainly being used, the spirit, where you have resins and alcohol, and oil, where you have linseed oil, resins and turpentine as a thinner. It's interesting, that you wrote about linseed oil, I didn't know that. I thought, that turpentine is more dangerous to breathe. Is walnut oil better?

For my taste, the unvarnished violin sounds a bit 'wild'. Varnish stiffens the plates, damps some frequencies and highlights some. I think, if one experiences, that unvarnished violin sound better for him, he can measure the effect of varnish on his plates(stiffness, weight, mode frequencies), and then make a violin in white, keeping those changes in mind.

[Arkcon]

Years ago, Scientific American had an article on the varnish used for a Stradivarius.  The varnish used in the article was a digest of shrimp shells in NaOH.  It made the sound of the violin much more improved over standard, said the article's expert -- in electron microscopy and violin playing.   The information is now repudiated, but still, its an exciting mix of art and science.

The composition of propolis varies from hive to hive, from district to district, and from season to season.  From Wikipedia.  So you're not going to easily know what's in propolis.  https://en.wikipedia.org/wiki/Propolis#Composition

[Civisover]

Yeah, there are a lot of articles and books about classical Italian varnish research, and all of them give pretty controversial results. If you are really interested, you can look through thouse two, for example.

So if we know the composition of propolis, what in your point of view would change color in basic environment?

[Enthalpy]

[...] So if we know the composition of propolis, what in your point of view would change color in basic environment?

I fear this question will make the experts here uncomfortable, because propolis' composition varies so much, because the colourful component may be unknown, and because even for one single well-known molecule, the mode of action of the pH (change the number of electrons in the coloured molecule or ion, change the absorption-damping processes...) must be investigated for some time before reaching a conclusion.

You might experiment a few different simple bases, neutralize them with a few varied simple acids, and check if it's the pH that determines the colour of propolis. If propolis needs strong basic conditions to offer the colour you like, it's probably inconvenient : corrosive, neutralized at the violin's heck by sweat.

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Linseed oil vs walnut oil vs health: I've no clear opinion about that. I've read conflicting claims, from "safe to ingest as long as it smells good" to "this made Van Gogh crazy". The hardening process by air is what must be avoided in ingested oil.

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Recent experiments suggest that Strad's reputation owes much to a collective behaviour effect, and other makers like Vuillaume produced better instruments (Hillary Hahn plays one), so studying their varnishes rather than again and again Strad's ones might be more useful.

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As you like to experiment, you may enjoy this proposal
http://www.scienceforums.net/topic/80768-violin-non-linearity/
It takes just one violin, two bows and two violinists, as Hoola suggested there in message #2. I won't try it myself because I left everything behind when I left my country. Quickly checked by ear, may tell something interesting, worth publishing.

[Civisover]

Thank you, Enthalpy for such a broad answer and for the link.

'You might experiment a few different simple bases, neutralize them with a few varied simple acids, and check if it's the pH that determines the colour of propolis' that's a great advice, thank you, will do.

Yes,I totaly agree with you, there were several double blind experiments, that showed, that modern violins sound better. But I'm interested in old Italian varnish not because of it's 'magic' effect on sound, but because of it's visual characteristics, which are incomparable even with the best contemporary violins.

[Enthalpy]

Ca(OH)₂ is easily available, KOH too, as is HCl. HNO₃ might spoil the attempt because it's an oxidizer, and H₂SO₄ makes some insoluble salts.
Comparing the effect of NaOH and NaCl on propolis would give a first hint whether it's Na⁺ or OH^- that gives the colour.
Besides weighing the compounds, litmus paper is a simple means to know the pH... if no compound overwhelms the paper's colour.

If your goal is a specific colour, my gut feeling is that pigment powders used by the artists who make their paints are the simple way. Some are inorganic metal compounds, stable over time and nicely inert (don't breathe them too much nevertheless), meant for mixing with oil, available in many shades and further mixable. They would avoid the introduction of NaOH in a varnish supposed to repel water.
https://en.wikipedia.org/wiki/Pigment
https://en.wikipedia.org/wiki/List_of_inorganic_pigments
most painters buy paints ready to use but I knew a shop selling the pigment powders.

Thanks for opening such a nice thread!

[Enthalpy]

These pigments have proven stable over time: