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MikeC

What's a good copal varnish recipe?

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On 10/12/2011 at 8:30 AM, MikeC said:

I have some gum copal, not sure what kind or origin, that's all the container says. Thinking of trying to make some varnish with it. I found this recipe

Take copal in powder, 1 oz.; essential oil of lavender, 2 oz.; essence of turpentine, 6 oz.

Put the essential oil of lavender into a matrass of a proper size, placed on a sand-bath heated gently. Add to the oil while very warm, and at several times, the copal powder, and stir the mixture with a stick of white wood rounded at the end. When the copal has entirely disappeared, add at three different times the essence almost in a state of ebullition, and keep continually stirring the mixture.

You varnish experts... Joe? What do you think of that recipe. Are there other recipes that you would recommend?

Most resins sold as 'copal' are almost insoluble in turpentine. Those are hard copals from Africa. I don't know however if adding lavender oil can change that.

I said 'almost insoluble' because I had made a jar with a hard Kopal (don't remember which one) and added turpentine to it. Now after 20 years or so I found the jar and the copal had liquified to maybe 80 percent.

However I wouldn't use it because it is too clear in color. When color is added, clear light colored varnishes protect colors very badly to my experience.

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On 5/20/2014 at 8:34 PM, Jeffrey Holmes said:

  I've also tried mastic, if very good quality, in substitution of the shellac.  I do add a little plasticizer as well, but only enough to make the varnish workable (not too chip-py).  I'll leave the choice of plasticizer to you.

I also occasionally use a little Manilla copal in retouch varnish, but at a much lower %.  More Sandarac, more light shellac, more plasticizer.

What is a plasticizer?

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A substance added to increase flexibility and to reduce brittleness.  Depending on the varnish and dried results I've seen various additives used; resins (elemi and others), castor oil, thickened linseed, glycerine, waxes, etc.

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Hi Mike-It could be the Congo copal I sent to you  years ago hoping to get other members  to know how to make that  type of varnish. Not easy. I lost my interest when I started to experiment with rosin. To my knowledge no researcher has found copal resins in Cremona varnishes, which is interesting for it could have been a common  commodity in some households for it was the only weatherproof coating they had at that time for horse carriages, etc.

Hope all is well and those Strads just keep coming. I stuffed my  bank box with Canadian dollars, out of the dollar. Bad move?

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One of the first varnishes I made and used was with Congo copal (from Woodfinishing Enterprises).  They said it had "already been run", which I guess means melted and cooled at higher temperature than it needs to melt now.  It was super-simple, just heat and melt the resin (I also added some damar), add some oil, and cool and thin, and that was it.  I didn't do anything fancy at all, and the varnish seemed fine... only not very colorful.  

I still have that varnish, along with a gazillion other kinds of varnish I cooked up.

The Congo copal resin I have dissolves well in xylene, and I have used it (with a bit of color added) as a first coat on the wood.  I have used lots of other things, too.

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8 hours ago, uncle duke said:

What is a plasticizer?

 

2 hours ago, Jeffrey Holmes said:
A substance added to increase flexibility and to reduce brittleness.  Depending on the varnish and dried results I've seen various additives used; resins (elemi and others), castor oil, thickened linseed, glycerine, waxes, etc.

My experience is that good plasticizers are larch turpentine and mastic. 

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Hi Fred good to hear from you.   I still have the Congo copal you sent me.   This thread originally started because I bought a container of what I think is probably Manilla copal from a website,  don't remember which site.  It was a cheap closeout special.    Unfortunately I got real lazy regarding making varnish and building violins but slowly getting back into it now.    

Canadian dollar vs. US dollar has been in a slow downtrend for a long time.   Short term it could go either way.  good luck!   I've moved away from currencies and got more into futures lately.   Maybe I'll have a real strad some day if I don't go broke first  :D 

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