Washing Linseed Oil

[Michael Szyper]

3 hours ago, Davide Sora said:

Hi Michael, may Iask what do you mean by "cold-combined the oil with the resin"?

Dissolve the resin in solvent, mix with linseed oil at room temperature without any heat. So no cooking of varnish involved actually.

[Davide Sora]

25 minutes ago, Michael Szyper said:

Dissolve the resin in solvent, mix with linseed oil at room temperature without any heat. So no cooking of varnish involved actually.

Thanks for the clarification. So do you think it's best not to cook the varnish? Some argue that in this way there will be no chemical bond between resin and oil, just a mix like in alcohol varnishes. Did I get it right?

[Michael Szyper]

20 minutes ago, Davide Sora said:

Thanks for the clarification. So do you think it's best not to cook the varnish? Some argue that in this way there will be no chemical bond between resin and oil, just a mix like in alcohol varnishes. Did I get it right?

You got it right. I do not claim it is best practice not to cook. It is just one of many different ways to prepare varnish. Sometimes I like it, sometimes not 

[JacksonMaberry]

I have yet to see a publication that adequately discusses this phenomenon of bonding between oil and resin that only occurs at temperature, but it's true this is an accepted wisdom about varnish. Earlier in this topic @Melvin Goldsmith, who has posted photos here copiously of his instruments and who has an outstanding record, has stated that he cold-compounds his varnish. 

While I am a "cooker", I am not so convinced that I am infallible as to ignore a person like Melvin (and he's not the only one, either) when he says "I don't cook". 

polymer chemistry is a "dark art", and even my friends at uni chem departments and pharmaceutical companies refuse to get into it. That tells me a lot.

[Davide Sora]

Making an oil varnish without cooking it has the advantage of maintaining a high fluidity of the solution with good self-spreading properties, particularly interesting especially for the colored coats. With cooking it is difficult to maintain this property, at least in my experience, unless you greatly increase the amount of oil compared to the resin. Perhaps the cold compound varnish could be less durable over time, but as it appears to be a typical feature of classical varnises, it could be spot-on.

[charliemaine]

11 hours ago, Michael Szyper said:

Maybe one thought about washing linseed. I had no problems with the unwashed oil as long as I cooked it separately and cold-combined the oil with the resin. When cooking the varnish, it seems to generate "worms" or "particles" if not properly washed. 

Did anyone else observed something similar? 

Jacob van Soelen(now deceased) and I both had experienced problems with varnish "seeding" or worms. We both experimented a lot with different oils and found that raw cold pressed oil properly washed solved our problems. Check out the older posts around 2012-13 on this subject. I tried to find one in particular by Jacob which is really good, but could not.

 

 

[charliemaine]

2 hours ago, Davide Sora said:

Making an oil varnish without cooking it has the advantage of maintaining a high fluidity of the solution with good self-spreading properties, particularly interesting especially for the colored coats. With cooking it is difficult to maintain this property, at least in my experience, unless you greatly increase the amount of oil compared to the resin. Perhaps the cold compound varnish could be less durable over time, but as it appears to be a typical feature of classical varnises, it could be spot-on.

Could be. Doesn't it come down to what each individuals goals are? Are we trying to emulate the properties of classical Italian varnish or not. Antique to look similar or not.

Davide your fiddles are so well made and look so good, do you really want the varnish to disappear and leave the wood less protected in a few years time? If so then why not just antique them to begin with? 

I'm also curious, as a native Italian living and making in Cremona, do you design your varnish to wear and look like the 17-18th century predecessors? Or do you want your varnish to wear in a different way? 

[JacksonMaberry]

12 minutes ago, charliemaine said:

Doesn't it come down to what each individuals goals are?

I personally think so. 

[MikeC]

how to you make a cold varnish?  Do you dissolve the rosins in alcohol and then mix with oil?  What will cooked rosin dissolve in besides alcohol? 

[JacksonMaberry]

13 minutes ago, MikeC said:

how to you make a cold varnish?  Do you dissolve the rosins in alcohol and then mix with oil?  What will cooked rosin dissolve in besides alcohol? 

For answer, see above post, quoted here for convenience:

2 hours ago, Michael Szyper said:

Dissolve the resin in solvent, mix with linseed oil at room temperature without any heat. So no cooking of varnish involved actually.

 

[Steve Voigt]

1 hour ago, JacksonMaberry said:

I have yet to see a publication that adequately discusses this phenomenon of bonding between oil and resin that only occurs at temperature, but it's true this is an accepted wisdom about varnish.

Here are a couple sources. I believe both articles are paywalled, but you can find them if you have institutional access.

"Reconstructing historical recipes of linseed oil/colophony: Influence of preparation processes on application properties." Tirat, Echard, et al. Journal of Cultural Heritage, Sept. 2017.

From the article: "In particular, it suggests that, for a given colophony proportion, there are threshold values of heating time and temperature below which colophony and oil cannot be mixed at the molecular level to produce a monophasic liquid system. "

Another source: "Copal varnishes used on 18th- and 19th- century carriages." Augerson, Christopher. Journal of the American Institute for Conservation, Spring/Summer 2011.

From the article: "Although it was long believed resin polymers formed cross-polymers during manufacture, this was proven only recently by Van den Berg et al (1999).* Their work showed that the copal polymer rearranges extensively and that the double bonds of fatty acids partly migrate during cooking, resulting in many partially unresolved isomeric structures. With artificially aged samples, the characteristic saturated fatty acids from the oils remained but the unsaturated ones reacted away completely, including the less reactive oleic acid…"

* Van den Berg, Horst, and Boon. "Recognition of copals in aged resin/oil paints and varnishes." ICOM committe for preservation preprints. 12th annual meeting, Lyon, ed. J. Bridgeland. (I've not yet looked for this reference)

An observation of my own, from outside the violin world: traditional paint is of course made by mixing (mulling) pigment and linseed oil. Normally the mixture, after drying, remains stable for a very long time. So if the resin is thought of as an unusually transparent pigment, then it may make sense, and it may not demix for a long time, if ever. However, there are durability issues to consider that are different from those with varnish. Linseed oil paint needs to be "rejuvenated" with oil every 5-10 years, and repainted every 20 or so (for exterior applications) because the linseed oil oxidizes on the surface. And of course on paintings, the paint is normally varnished.

I'm not passing judgement on anyone's work here, just pointing out that (1) there is strong evidence, both scientific and practical, that cooking does change the nature of the mixture; and (2) the durability issues will be quite different in a cold-compounded mixture.

[JacksonMaberry]

3 minutes ago, Steve Voigt said:

Here are a couple sources. I believe both articles are paywalled, but you can find them if you have institutional access.

"Reconstructing historical recipes of linseed oil/colophony: Influence of preparation processes on application properties." Tirat, Echard, et al. Journal of Cultural Heritage, Sept. 2017.

From the article: "In particular, it suggests that, for a given colophony proportion, there are threshold values of heating time and temperature below which colophony and oil cannot be mixed at the molecular level to produce a monophasic liquid system. "

Another source: "Copal varnishes used on 18th- and 19th- century carriages." Augerson, Christopher. Journal of the American Institute for Conservation, Spring/Summer 2011.

From the article: "Although it was long believed resin polymers formed cross-polymers during manufacture, this was proven only recently by Van den Berg et al (1999).* Their work showed that the copal polymer rearranges extensively and that the double bonds of fatty acids partly migrate during cooking, resulting in many partially unresolved isomeric structures. With artificially aged samples, the characteristic saturated fatty acids from the oils remained but the unsaturated ones reacted away completely, including the less reactive oleic acid…"

* Van den Berg, Horst, and Boon. "Recognition of copals in aged resin/oil paints and varnishes." ICOM committe for preservation preprints. 12th annual meeting, Lyon, ed. J. Bridgeland. (I've not yet looked for this reference)

An observation of my own, from outside the violin world: traditional paint is of course made by mixing (mulling) pigment and linseed oil. Normally the mixture, after drying, remains stable for a very long time. So if the resin is thought of as an unusually transparent pigment, then it may make sense, and it may not demix for a long time, if ever. However, there are durability issues to consider that are different from those with varnish. Linseed oil paint needs to be "rejuvenated" with oil every 5-10 years, and repainted every 20 or so (for exterior applications) because the linseed oil oxidizes on the surface. And of course on paintings, the paint is normally varnished.

I'm not passing judgement on anyone's work here, just pointing out that (1) there is strong evidence, both scientific and practical, that cooking does change the nature of the mixture; and (2) the durability issues will be quite different in a cold-compounded mixture.

That's what I was wanting, thanks Steve!

[Michael Szyper]

42 minutes ago, Steve Voigt said:

Here are a couple sources. I believe both articles are paywalled, but you can find them if you have institutional access.

"Reconstructing historical recipes of linseed oil/colophony: Influence of preparation processes on application properties." Tirat, Echard, et al. Journal of Cultural Heritage, Sept. 2017.

From the article: "In particular, it suggests that, for a given colophony proportion, there are threshold values of heating time and temperature below which colophony and oil cannot be mixed at the molecular level to produce a monophasic liquid system. "

Another source: "Copal varnishes used on 18th- and 19th- century carriages." Augerson, Christopher. Journal of the American Institute for Conservation, Spring/Summer 2011.

From the article: "Although it was long believed resin polymers formed cross-polymers during manufacture, this was proven only recently by Van den Berg et al (1999).* Their work showed that the copal polymer rearranges extensively and that the double bonds of fatty acids partly migrate during cooking, resulting in many partially unresolved isomeric structures. With artificially aged samples, the characteristic saturated fatty acids from the oils remained but the unsaturated ones reacted away completely, including the less reactive oleic acid…"

* Van den Berg, Horst, and Boon. "Recognition of copals in aged resin/oil paints and varnishes." ICOM committe for preservation preprints. 12th annual meeting, Lyon, ed. J. Bridgeland. (I've not yet looked for this reference)

An observation of my own, from outside the violin world: traditional paint is of course made by mixing (mulling) pigment and linseed oil. Normally the mixture, after drying, remains stable for a very long time. So if the resin is thought of as an unusually transparent pigment, then it may make sense, and it may not demix for a long time, if ever. However, there are durability issues to consider that are different from those with varnish. Linseed oil paint needs to be "rejuvenated" with oil every 5-10 years, and repainted every 20 or so (for exterior applications) because the linseed oil oxidizes on the surface. And of course on paintings, the paint is normally varnished.

I'm not passing judgement on anyone's work here, just pointing out that (1) there is strong evidence, both scientific and practical, that cooking does change the nature of the mixture; and (2) the durability issues will be quite different in a cold-compounded mixture.

I am having hard times to believe that a cold mixed resin-oil varnish is a suspension. You might be right, but during polymerization there is a lot of stuff going on, possibly linking between resin and oil, too. The mix of oil, solvent and resin (so before application) I would rather call a solution than a suspension. 

[JacksonMaberry]

2 minutes ago, Michael Szyper said:

I am having hard times to believe that a cold mixed resin-oil varnish is a suspension. You might be right, but during polymerization there is a lot of stuff going on, possibly linking between resin and oil, too. The mix of oil, solvent and resin (so before application) I would rather call a solution than a suspension. 

Michael, you're correct here. If a resin (say, colophony) and an oil (linseed) are mutually soluble, which they are, then you have a solution and not a suspension. So a cold mixed varnish made of linseed oil and a non-polar resin like colophony is certainly not a suspension.

[JacksonMaberry]

26 minutes ago, JacksonMaberry said:

Michael, you're correct here. If a resin (say, colophony) and an oil (linseed) are mutually soluble, which they are, then you have a solution and not a suspension. So a cold mixed varnish made of linseed oil and a non-polar resin like colophony is certainly not a suspension.

That said, just because something is in solution does not mean "crosslinking" is taking place, and such crosslinking is something of an obsession amongst trades that use varnish even when it is difficult for non polymer specialists (and I am *not* a polymer specialist, nor do I claim to understand it) to understand.

[Steve Voigt]

15 minutes ago, Michael Szyper said:

I am having hard times to believe that a cold mixed resin-oil varnish is a suspension. You might be right, but during polymerization there is a lot of stuff going on, possibly linking between resin and oil, too. The mix of oil, solvent and resin (so before application) I would rather call a solution than a suspension. 

Hi Michael,

I'm not totally sure I understand your point, since I didn't use the words "suspension" or "solution." But I agree that the resin/oil mixture is a solution, not a suspension, since it's transparent. I meant the comparison to paint as an analogy; I didn't mean to suggest that the resin/oil mixture was actually a paint--sorry if I created that impression! However, suspensions and solutions are both mixtures, whereas a (properly) cooked varnish appears to be a compound. To me that's the important difference.

In any case, the sources I listed are probably a better guide than my speculations!

[charliemaine]

Older threads with good relative info...

https://briscdisc.silverbrush.co.za/

 

 

[Davide Sora]

6 hours ago, charliemaine said:

Could be. Doesn't it come down to what each individuals goals are? Are we trying to emulate the properties of classical Italian varnish or not. Antique to look similar or not.

Davide your fiddles are so well made and look so good, do you really want the varnish to disappear and leave the wood less protected in a few years time? If so then why not just antique them to begin with? 

I'm also curious, as a native Italian living and making in Cremona, do you design your varnish to wear and look like the 17-18th century predecessors? Or do you want your varnish to wear in a different way? 

Not exactly, although I did this for a while when using oil/rosin varnish (self made). As beautiful as it is, is exposed to very rapid wear at the contact points, so I went back to using my linoxin/shellac varnish, which although comparable in mechanical strength, is much more resistant to wear caused by sweat at the points of contact. Although it doesn't last forever, it lasts longer. I am not obsessed with reproducing the look of old varnishes with their peculiar wear, otherwise I would make copies, which I refuse to do even when I receive specific requests in that sense. I prefer to make my own violins which will wear out in their own peculiar way, perhaps 200 or 300 years from now it won't make much difference.

[Jim Bress]

21 hours ago, JacksonMaberry said:

I have yet to see a publication that adequately discusses this phenomenon of bonding between oil and resin that only occurs at temperature, but it's true this is an accepted wisdom about varnish. Earlier in this topic @Melvin Goldsmith, who has posted photos here copiously of his instruments and who has an outstanding record, has stated that he cold-compounds his varnish. 

While I am a "cooker", I am not so convinced that I am infallible as to ignore a person like Melvin (and he's not the only one, either) when he says "I don't cook". 

polymer chemistry is a "dark art", and even my friends at uni chem departments and pharmaceutical companies refuse to get into it. That tells me a lot.

An article from my "dark arts" folder.

Historical linseed oil colophony varnishes formulations.pdf

[Davide Sora]

Another interesting article on the oil/rosin ratio:

https://www.researchgate.net/publication/319482093_A_step_forward_in_disclosing_the_secret_of_Stradivari's_varnish_by_NMR_spectroscopy

In their conclusions they state:

"It should be noted that mixture composition that provides the most homogeneous coating (75/25 w/w) roughly corresponds to a 1:1 stoichiometric ratio, if abietic acid and tri-linolenic glyceride are taken as representative compounds for colophony and linseed oil, respectively."

So it seems that to get a 1:1 stochiometric ratio for the best oil / rosin combination, a ratio of 3:1 oil/rosin by weight would be the most appropriate. Looks like a +1 for long oil varnishes.

 

[JacksonMaberry]

32 minutes ago, Davide Sora said:

Another interesting article on the oil/rosin ratio:

https://www.researchgate.net/publication/319482093_A_step_forward_in_disclosing_the_secret_of_Stradivari's_varnish_by_NMR_spectroscopy

In their conclusions they state:

"It should be noted that mixture composition that provides the most homogeneous coating (75/25 w/w) roughly corresponds to a 1:1 stoichiometric ratio, if abietic acid and tri-linolenic glyceride are taken as representative compounds for colophony and linseed oil, respectively."

So it seems that to get a 1:1 stochiometric ratio for the best oil / rosin combination, a ratio of 3:1 oil/rosin by weight would be the most appropriate. Looks like a +1 for long oil varnishes.

 

Ahhh, thank you! Fascinating, Davide. I have not experimented much with anything that long, but in general with rosin or rosinate (inclusive of lined rosin) prefer a 3:2 oil to resin ratio to anything shorter as performance is concerned. Ultimately I think it's, within reason, very personal and that many things can work. For a varnish ground that is in the wood, I think there is a lot more latitude, since what's in the wood doesn't seem to have to follow the fat over lean maxim, but for everything else I feel that from my experiments anything from (oil:resin) 2:1 to 1:1 can perform. I'd rather go fatter than leaner. Anything that scratches white or chips off when you look at it askance is a no go for me.

[charliemaine]

1 hour ago, Davide Sora said:

So it seems that to get a 1:1 stochiometric ratio for the best oil / rosin combination, a ratio of 3:1 oil/rosin by weight would be the most appropriate. Looks like a +1 for long oil varnishes.

Interesting article...The only 3:1 oil/resin varnish made commercially that I know of is Donald Fels' Alchemist Varnish. I also remember Brian Lisus mentioning that he uses a 60:40 oil/resin ratio to make his varnish. I'm not sure but Magister varnish seemed to be on the long side, which makes sense since Koen and Mr Fels were colleagues. 

[JacksonMaberry]

I wonder where the obsession within the lutherie business for very short varnishes came from? I've gotten the sense that we're growing out of it gradually though, which is refreshing.

[charliemaine]

6 minutes ago, JacksonMaberry said:

I wonder where the obsession within the lutherie business for very short varnishes came from? I've gotten the sense that we're growing out of it gradually though, which is refreshing.

Lean varnishes work better if your goal is to make copies that emulate classical Italian varnish.

[JacksonMaberry]

23 minutes ago, charliemaine said:

Lean varnishes work better if your goal is to make copies that emulate classical Italian varnish.

That's debatable. As I pointed out earlier in the topic and Melvin echoed, the behavior of the classical films today is not indicative of it's behavior when new - again, linseed oil films change substantially over time in both composition and mechanical properties. Among other things they become much more brittle than the were originally, as well as less durable to chemical attack. 

If you use a varnish that behaves now as these Cremona varnishes behave at 300+ years old, imagine what yours will be like in a few centuries. Not ideal.

Edit: I think I misread your point - maybe you were saying that, if you're making a copy and want it to act now how the old ones do today you'd use leaner? I could understand that, but still wouldn't do it myself for the above reasons