Sign in to follow this  
Michael.N.

Varnish, quick and dirty.

Recommended Posts

I had some unused colophony left over from a batch of varnish that I made many years ago. The varnish turned out well but I promised myself that I would never make it again. Fumes, neighbours - no need to explain further.

Then I came across the Courtnall/Johnson low temperature recipe. In went the colophony, heated to the point that it melted, which was around 110 C. I didn't have any linseed so I substituted some supermarket walnut oil that I had. I cooked together at 125 C for just over an hour. 45/55 oil to resin, no mastic. It had great clarity whilst hot but after I decanted it into a jar the varnish turned rather cloudy and murky looking.  It had very little colour but at least it was clear enough when put on wood. A bit of a slow drier as it takes around 14 hours to become touch dry (UV cabinet). It was also sensitive to heat, taking a thumb print even after a few months of drying.

Today I decided to put this varnish back in the pan. Another hour at 125 C but this time I spiked it to 160 C, perhaps just for 5 minutes or so before allowing it to settle back at 125 C. Now it's back in the jar and the murky looking varnish is now very clear. I suspect it will still be a little slow to dry. little colour and still heat sensitive. I'll find out soon enough.  I'm now tempted to make another batch but using linseed, up the ratio to 60/40 and perhaps add a little lime. The fumes were nothing like the high temperature treatment of rosin, thankfully. In actual fact I did it all indoors but it was a very small batch.

Share this post


Link to post
Share on other sites

No, more like 1". I'll try it on wood today and find out how it dries over the next few weeks. This is all experimental, it's highly unlikely to be used on actual instruments - unless it proves itself over time.

What is the purpose of the lime? Presumably it adjusts the ph but I've also read that it helps prevent imprinting, is that the case?

Share this post


Link to post
Share on other sites
8 minutes ago, Marty Kasprzyk said:

 

I use Birchwood Casey Tru Oil stock finish.  It dries real fast and doesn't have that annoying red color you often see on Strad violins.

Oh Marty you're breakin' my heart....

Share this post


Link to post
Share on other sites
5 minutes ago, joerobson said:

Oh Marty you're breakin' my heart....

Joe, are you heartbroken because of the Tru Oil or the annoying red color?  No more cochineal for you!  ;-)

Share this post


Link to post
Share on other sites
6 hours ago, Michael.N. said:

No, more like 1". I'll try it on wood today and find out how it dries over the next few weeks. This is all experimental, it's highly unlikely to be used on actual instruments - unless it proves itself over time.

What is the purpose of the lime? Presumably it adjusts the ph but I've also read that it helps prevent imprinting, is that the case?

The pill length indicates how fast the varnish will dry (crosslink or polymerize). 4 inches is my minimum pill. The calcium adds luster,  a little color, and hardness.

Share this post


Link to post
Share on other sites

Well I suppose I could always put it back in the pan, cook longer or take the heat towards 200 C. It's all good experience. I don't know if it's too late to add the lime but I can try that too.

Share this post


Link to post
Share on other sites
6 hours ago, Michael_Molnar said:

The pill length indicates how fast the varnish will dry (crosslink or polymerize). 4 inches is my minimum pill. The calcium adds luster,  a little color, and hardness.

Neat!

But calcium in the cooking, forming calcium rosinate, may add also an annoying water sensitivity......have you ever noticed this?

Share this post


Link to post
Share on other sites
6 hours ago, Davide Sora said:

Neat!

But calcium in the cooking, forming calcium rosinate, may add also an annoying water sensitivity......have you ever noticed this?

I have noticed a faint stain pattern in reflected light, but it buffs out. I don't know if that is it.

Share this post


Link to post
Share on other sites

Hello
Varnish you have to cook as long as you make the pill length.
When it is not, no oil is involved in the resin
When cooked at a low temperature around 100 - 120 C it may take about 100 hours

Generally low temperature - longer cooking time - lighter colors
                Higher temperature (more than 200 C) - shorter cooking time - darker color
There is a lot of writing on the pegbox about how to do it -

Share this post


Link to post
Share on other sites
5 hours ago, Michael_Molnar said:

I have noticed a faint stain pattern in reflected light, but it buffs out. I don't know if that is it.

I have some few years old samples of varnish made with rosin cooked with calcium hydroxide (about 8%, maybe too much) and linseed oil 1:1 ratio that, when moistened with water develops a tackiness to the touch, not so much but you can feel it under your fingers.
This worries me, and the literature is fairly clear about the water sensitivity of calcium resinates.
So I prefer to use the advantage of hardening caused by calcium only for the ground layers but not for the upper and top layers to avoid this possible worrying drawback.
I also noticed that increasing the oil to rosin ratio (1,5:1 or 2:1) solves this problem, but this way you lose the advantage of hardening.
I was just curious if others had noticed this problem, since the use of limed varnishes is quite widespread and I wondered if this could be an advantage for those who make antiqued finishes (easier to wear down and maybe then protected by layers of shellac as the old instruments to overcome this problem) but that is not acceptable in the "real world" of new instruments making.


 

 

Share this post


Link to post
Share on other sites

My experience has been that without the lime, the varnish will eventually darken and become extremely brittle (perhaps from the long-term effect of the acidic rosin on the linseed oil component?).

Share this post


Link to post
Share on other sites

how acidic is rosin?   The Keith Hill recipe uses wood ash lye as the base.  Do any of you have experience with that? 

Share this post


Link to post
Share on other sites
1 hour ago, MikeC said:

how acidic is rosin?   The Keith Hill recipe uses wood ash lye as the base.  Do any of you have experience with that? 

All I've run across are "acid numbers", which refer to the number of milligrams of potassium hydroxide it takes to neutralize one gram of rosin. The acid number is around 150-180. For comparison, Dammar and elemi are about 25.

Share this post


Link to post
Share on other sites
3 hours ago, David Burgess said:

My experience has been that without the lime, the varnish will eventually darken and become extremely brittle (perhaps from the long-term effect of the acidic rosin on the linseed oil component?).

 

1 hour ago, David Burgess said:

All I've run across are "acid numbers", which refer to the number of milligrams of potassium hydroxide it takes to neutralize one gram of rosin. The acid number is around 150-180. For comparison, Dammar and elemi are about 25.

This is probably true (I use probably because I'm not a chemist and I really don't know exactly.....:unsure:) and cooking with metals has the primary purpose of lowering acidity, but calcium is not the only one and even if probably the most efficient in this regard, zinc probably should do the same without the disadvantage of water sensitivity, ash lye (a mineral mix) is another possibility but I again I don't really know, and sure there are other possibility.

The "problem" is that the analysis of ancient varnish almost always find plenty of calcium, so everyone is induced to use calcium, but in reality no one knows for sure where it comes from, and perhaps precisely this moisture sensitivity may have had a role in the rapid consumption of these varnishes, who knows.

The other "problem" is whether you want to try to accurately replicate the old varnishes with all their defects, or if you want to try to improve them in their protective properties by increasing their durability.

There are other resins better than rosin to be used with a natural lower acidity, but the high acidity of rosin is what makes it react and is the responsible for color change with cooking, and that is a really nice thing.

Obviously I do not have definitive answers to these "problems" but are things I always think and that make me headache, so it's nice and interesting to hear the opinions and any conclusions of other people on these subjects.

 

 

Share this post


Link to post
Share on other sites
5 hours ago, Davide Sora said:
I was just curious if others had noticed this problem, since the use of limed varnishes is quite widespread and I wondered if this could be an advantage for those who make antiqued finishes (easier to wear down and maybe then protected by layers of shellac as the old instruments to overcome this problem) but that is not acceptable in the "real world" of new instruments making.

I had it twice. Very irritating. I tried protect with shellac 2nd time and it didn't work either. 

Share this post


Link to post
Share on other sites
6 hours ago, Davide Sora said:
 
I have some few years old samples of varnish made with rosin cooked with calcium hydroxide (about 8%, maybe too much) and linseed oil 1:1 ratio that, when moistened with water develops a tackiness to the touch, not so much but you can feel it under your fingers.
This worries me, and the literature is fairly clear about the water sensitivity of calcium resinates.
So I prefer to use the advantage of hardening caused by calcium only for the ground layers but not for the upper and top layers to avoid this possible worrying drawback.
I also noticed that increasing the oil to rosin ratio (1,5:1 or 2:1) solves this problem, but this way you lose the advantage of hardening.
 
I was just curious if others had noticed this problem, since the use of limed varnishes is quite widespread and I wondered if this could be an advantage for those who make antiqued finishes (easier to wear down and maybe then protected by layers of shellac as the old instruments to overcome this problem) but that is not acceptable in the "real world" of new instruments making.
 
2

Davide, I add 1 or 2 gm per 300 gm of rosin. However, I do not measure this. I watch when the slaked lime forms little flakes. Then I stop squirting a slurry of lime water. The water turns to steam that kicks off a reaction.

My understanding is that we want to reduce the acidity, not nuke it. Rosin is comprised of a host of acids (90%) with abietic acid being the largest component. Eliminating it means that you converted all of the rosin's abietic acid to a soap. I guess this is what you are doing which is like Michelman's rosinate varnishes. I don't do this.

BTW, re-read the seminal article by Geary Baese in Strad July 1996.

5 hours ago, MikeC said:

how acidic is rosin?   The Keith Hill recipe uses wood ash lye as the base.  Do any of you have experience with that? 

Very. It is ~90% organic acids. Read this.

5 hours ago, David Burgess said:

My experience has been that without the lime, the varnish will eventually darken and become extremely brittle (perhaps from the long-term effect of the acidic rosin on the linseed oil component?).

I too think some calcium stabilizes the varnish. I recall reading somewhere about this. It also warned how unstable iron is. I should have kept that source. I think the calcium takes the edge off the strong acidic nature of rosin. 

Share this post


Link to post
Share on other sites
1 hour ago, Michael_Molnar said:

Davide, I add 1 or 2 gm per 300 gm of rosin. However, I do not measure this. I watch when the slaked lime forms little flakes. Then I stop squirting a slurry of lime water. The water turns to steam that kicks off a reaction.

My understanding is that we want to reduce the acidity, not nuke it. Rosin is comprised of a host of acids (90%) with abietic acid being the largest component. Eliminating it means that you converted all of the rosin's abietic acid to a soap. I guess this is what you are doing which is like Michelman's rosinate varnishes. I don't do this.

 

True, my first attempts were influenced by Michelmann resinates but I abandoned the idea as a resin source.

Using a smaller amount of calcium (1 or 2% max, similar tecnique as yours) and adding a little more oil the problem seems more manageable, but I really don't know how much the acidity is reduced.
I think that also cooking at higher temperature aid to reduce acidity.
I have yet to try cooking rosin with zinc sulfate alone.

 

Share this post


Link to post
Share on other sites

There is probably a lot of factors involved that speaks for or against liming (cooking time, temperature, quality of colophony/linseed oil etc. etc)

I don't lime anymore because it makes the varnish too hard for my taste and the batches without lime is more durable to sweat.

It has been bad summer weather here in Finland, but as soon as it gets better I'm going to cook some dark varnish.

Batch from 2014 is still as good as new so I think that well cooked varnish lasts for years.

http://www.thestradsound.com/varnish

 

 

Share this post


Link to post
Share on other sites

Can anyone verify if long cooking of the rosin reduces the acid component? I think Fred N might have said something about this back in the dawn of history. I,be been adding lime at about two,three percent , but with long cook rosin maybe not needed, also recall that RodgerH does not add any lime to his long cook rosin.....interesting that limed varnish might be more hydroscopic.? Will the wonders never cease?

Share this post


Link to post
Share on other sites
15 minutes ago, James M. Jones said:

Can anyone verify if long cooking of the rosin reduces the acid component? I think Fred N might have said something about this back in the dawn of history. I,be been adding lime at about two,three percent , but with long cook rosin maybe not needed, also recall that RodgerH does not add any lime to his long cook rosin.....interesting that limed varnish might be more hydroscopic.? Will the wonders never cease?

Mike, 

At Thrift's Workshop, you saw me wet sand a varnish coat to reduce its thickness and highlight the ground. That varnish is made with limed cooked rosin ("black pitch"). There were no issues with water. That violin is hanging in my shop beautiful as ever. 

The Other Mike

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.