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Colophony Varnish Alcohol Soluble?


Shunyata

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I have a freshly varnished violin.  I made my own varnish following Hargrave’s recipe.

My skin dissolves varnish like crazy, so I thought to French polish to protect the varnish.

I tested alcohol on a freshly varnished swatch… a few hours sunlight and a week sitting around to cure.  It was at least fingernail hard. The alcohol caused the varnish to tack and lifted some color.  Did not use any linseed oil for lubricant.

Is this due to insufficient curing or is colophony inherently alcohol soluable?  Is it possible to French polish?

I don’t want to crap up my new instrument!

 

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Yes, alcohol can soften and melt oil varnish. Leaving oil varnish to cure longer, and French polishing with a little lubricant can reduce the risk of messing the oil varnish.  

If you want to French polish with shellac and build it up in layers as protection, you may need to be very patient to wait for weeks if not months for the oil varnish to dry really well before polishing. Otherwise, you'll get funny crackling (not nice crackling people admire) on the surface later.  

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Good advice from the comrades above. 

Oil varnishes in general (with some caveats and exemptions, it's not a monolith) experience a very interesting "solubility life cycle". Most remain sensitive to alcohol in their early life - this decreases over time to a state of near or total insolubility. However, it will gradually become soluble again, and by the time a hundred or two years have passed, it will typically become totally soluble again. The experiments of some European 18th century tinkerers, commented on by Charles Burney, observed such solubility on cremonese fiddles that even some wine damaged the varnish.

Folks that make a linoxyn spirit varnish (I believe Davide Sora is one?) Capitalize on this solubility life cycle of drying oil films to great effect by exploiting an accelerated curing methodology. 

I am not qualified to comment as to the nature of the chemistry that underpins this phenomenon, unfortunately. As both of my PhD chemist friends have told me, what's going on with varnish chemistry is dizzyingly complex. 

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Fresh oil varnish is reactive meaning that it will react with the french polish.  It is tricky to get the initial coats on a freshly varnished instrument without lifting the varnish if you use a pad.  Alcohol alone is a good method of removing oil varnish when you make a mistake.

Here is a way to safely french polish it:  use the air brush to spray a coat of shellac over the entire instrument.  Allow to dry overnight.  Now, french polish.  When you start lifting the early coats, stop and allow to dry.  Repeat using the pad until you get the beautiful but muted shine.

 

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I have not experienced problems french polishing oil varnish. If your technique is good the solvent will evaporate too fast to damage the oil. Even if your technique is not so great, probably still, because alcohol does not immediately destroy oil varnish like it does spirit varnish.

That said I have also stripped oil varnish with alcohol.

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3 hours ago, Christopher Jacoby said:

Depends how you cook it, and how much oil is in it, too. If you cook your oil and resin together for a long time after combining them it becomes less soluble to solvents

Yup. As with most things having to do with violins, "it depends". Dogmatic, "one size fits all" answers are seldom correct, regardless of their appeal.

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