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Straight colophony sealer


Deo Lawson
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Hi all,

In preparation for my next 5 string I'm settling on a new varnishing procedure. I've found that shellac and vernice bianca don't play nice with my amber varnish—the finish lacks that refractive sparkle when combined with either of those.

I'm curious about ordinary rosin as a sealer. I've tried some dissolved in alcohol and found that it works well visually with my varnish. My concern is that it never really feels dry. Even after some time in a dehydrator my test strips are sticky and I worry that the rosin dries soft after it's been dissolved (crystal structure?).

Do I need to wait longer, or should I cook down my rosin? Is it better when dissolved in turpentine? I'm not making a colophony varnish as I don't want any oil on the bare wood.

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Cook the rosin and use turpentine essence as a solvent, and a UV box for at least 24 hours to dry.

Or use Mastic instead of colophony, always with the essence of turpentine as a solvent and UV box to dry. The mastic is a low-acidity resin while the acidity of the rosin is high, hence the need to cook it for a long time or at a high temperature to reduce it. Find a lot about this on Maestronet. You can also "cook" the mastic if you want to harden it and make it more brittle, but just a few minutes at melting temperature on the hot plate is enough.

Just my two cents.

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11 minutes ago, Don Noon said:

I have a preference for terpene resin at the moment, it adds a little reddish color, nicer than colophony IMO.

Are you talking about the "Fulton" resin obtained from the essence of turpentine? I tried it too and works well, with the advantage of having very low acidity, if you have the patience to make it.:)

However, I would still prefer it in its clear version, otherwise even with normal rosin you could get redder or more intense colors with prolonged or hotter cooking. But too much color tends to stain and I'm not convinced by this, I prefer to limit the effect of this type of ground to increase the brightness of the wood figure without adding too much color, lot of ways to skin the rabbit.

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While I don't see any issue with using cold solved resins per se, it could be interesting to examine some things. 

These resins all have pretty low melting points, and by solving them, you're not changing that - you apply the solution, the solvent evaporates, and the resin goes on behaving as it always has. These resins haha a good relationship to wood vis a vis RI (refractive index), and so they look quite nice. Mechanically though, you've put something into the wood that will soften should the instrument get too hot. 

Now while that seems possibly concerning, given that the resin is in the wood rather than on it, it might not really matter at all. Stuff that is in the wood doesn't play by the same rules, after all. 

Let's turn to what you said here:

"I'm not making a colophony varnish as I don't want any oil on the bare wood."

This is a sentiment shared by many, so you're not alone, but it's perhaps wide of the mark. Ask yourself why you feel this way. There are quite a lot of very well regarded makers alive to say and in the past that do ground with oil or an oil containing varnish, and it hasn't slowed them down. Like any approach, it has to be done correctly, skillfully, and with the right materials. A wrong way to do it would be to saturate plates with oil, in the way Michelman discusses in his book. While it will look good, the resulting composite material will not perform well. 

On the flip side though, some really good science, such as that of Echard and others, have shown oil, or oil and resin (ie varnish) in the upper cells of the wood on classic Cremonese, including Stradivari. That shows that there was, in fact, oil going on bare wood, that it was being done at the highest levels, and that it worked well. 

All of which to say - question everything, especially absolutes (ie "never put oil on bare wood"). The violin business is filled with all sorts of folkloric and superstitious, absolutist belief. 

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Thank you all! I will try cooking down. I am not interested in mastic because.. it is rather expensive and I would rather chew it ^_^

 

As for the avoidance of oil on wood, I do it because I once visited a maker who applied oil varnish directly to his instruments with no sealer-just a very thick (undiluted) initial coat. His instruments sounded like they were stuffed with socks. What makes this experience more interesting is that his wife was also a maker, and she used almost identical techniques, but she sealed her instruments. Hers were quite nice violins.

I think I would like something that can dry on its own as opposed to oil, which will be polymerizing inside the wood for years. What I'm looking for is stiffness as well as optical qualities.

 

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7 minutes ago, Davide Sora said:

Are you talking about the "Fulton" resin obtained from the essence of turpentine? I tried it too and works well, with the advantage of having very low acidity, if you have the patience to make it.:)

However, I would still prefer it in its clear version, otherwise even with normal rosin you could get redder or more intense colors with prolonged or hotter cooking. But too much color tends to stain and I'm not convinced by this, I prefer to limit the effect of this type of ground to increase the brightness of the wood figure without adding too much color, lot of ways to skin the rabbit.

I'd agree with the general idea here, Davide. While I still like to build some color before varnishing, in my case with oxidation, as I have gotten older and seen more old violins of note, I have become more convinced we tend to overdo it. Some color can only come with time, but what is important from the beginning is to maximize the brightness and contrast, enhancing the optical properties inherent to the wood.

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3 minutes ago, Deo Lawson said:

Thank you all! I will try cooking down. I am not interested in mastic because.. it is rather expensive and I would rather chew it ^_^

 

As for the avoidance of oil on wood, I do it because I once visited a maker who applied oil varnish directly to his instruments with no sealer-just a very thick (undiluted) initial coat. His instruments sounded like they were stuffed with socks. What makes this experience more interesting is that his wife was also a maker, and she used almost identical techniques, but she sealed her instruments. Hers were quite nice violins.

I think I would like something that can dry on its own as opposed to oil, which will be polymerizing inside the wood for years.

 

I can understand why that would put you off! However, I will suggest that while he might be using good materials, his method seems to be slowing him down. 

Instead, imagine the following: an oil varnish, made carefully with materials prepared well. The oil was cold pressed, washed thoroughly, and is on its own very siccative. It was cooked expertly with resin, and a thin coat dries in UV to the point that it will not take an imprint after a day of curing. 

This varnish, which is say the consistency of room temp honey, is rubbed onto wood with an old handkerchief and the excess is buffed off likewise. The maximum penetration of this varnish is a few microns. It cures fine and does not penetrate further.

The above is not hypothetical, but rather the practice of quite a lot of good makers. With a small change, namely the use of a mineral filler, that's what Hargrave and others of his cohort are doing. Even with the plaster filler, there is still some mechanical coupling of the varnish with the wood surface, elsewise there would be greater difficulty with adhesion than is happening. I do it without a mineral filler, and my instruments looks nice and sound good, according to those that use them at least. My own assessment of my work is less flattering. And I'm not alone in these methods! 

All of which to say - it's not just what you use, often, but how you use it.

Trying this with inferior oil or inferior varnish can cause major issues. 

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1 hour ago, Davide Sora said:

Are you talking about the "Fulton" resin obtained from the essence of turpentine?

But too much color tends to stain...

Yep, the Fulton oxidized turpentine cooked cautiously outdoors, watched constantly  from upwind to avoid the noxious fumes.

I agree about avoiding too much color on the wood.  The terpene looks dark in solid form, but I have never seen it go over the edge to excessive color when used as a ground/sealer.  I have cooked colophony several times, and it's not quite as nice to my eye.  But the difference is small, and probably hard to see any difference under varnish.

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3 hours ago, Don Noon said:

Yep, the Fulton oxidized turpentine cooked cautiously outdoors, watched constantly  from upwind to avoid the noxious fumes.

I agree about avoiding too much color on the wood.  The terpene looks dark in solid form, but I have never seen it go over the edge to excessive color when used as a ground/sealer.  I have cooked colophony several times, and it's not quite as nice to my eye.  But the difference is small, and probably hard to see any difference under varnish.

In fact it is a beautiful resin that works really well, I had made some when I was in the mood to experiment something new, I still have a bottle of oxygenated turpentine waiting to be cooked and transformed into resin. Who knows, sooner or later I will, but for the moment I do not have a suitable place to avoid intoxicating myself with the fumes or unleashing the retaliation of the neighbors.:)

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