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Solvent Used In Varnishmaking...


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I wondered whether another solvent, other than turps,which I use, might give me a more consistent layer, even in several coats. Is this the reason you varnish before the last coat seals?

Many thanks,

Conor

Conor,

If you can find Stoddard Solvent it should do well in your situation. Stoddard is a very pure, high bp mineral spirit.....greasy without the residue problems of kerosene and lamp oil.

When oil and resin have truly bonded, as opposed to resin just melting in the oil, a sample of the cooled liquid will form a temporary string when you stick your finger in a small puddle and pull it away, kind of like what happens when you pull a spoon out of honey. The less viscous the varnish, the faster you need to do this to form the string.

If the components haven't bonded adequately, you can't really pull a string no matter how fast you do it. Well, you can sort of, but it doesn't look or act the same as when things are bonded. It's hard to describe. After you've compared the two a few times, you'll know right away.

Well said David.

Solvents...

Turpentine. When I talk about cooking a solvent into varnish and say that turpentine is the only thing it is because only turpentine will facilitate the mutual bonding of the materials, which is a physical and chemical bond having little to do with viscosity. As this is done at very high temperatures and is therefore quite dangerous, I choose not to discuss the details of the process. I will say though, that batch size has a huge impact on this process. Most of you are cooking in extremely small batches. This makes temperature control difficult to impossible. When you add the volativity of cooking turpentine at high temperature you verge on explosive. Tack time and drying [curing] time are very different varnish properties and only slightly related as far as formulations are concerned. Turpentine will effectively drop viscosity but will shorten the dry to tack time.

Mineral spirits [ Stoddard solvent, Gamsol, white spirit, naptha.. etc....petroleum derived solvents] are differentiated by the combination of bp's in the mix. All of them should solve the varnish and drop viscosity. The higher the bp solvent you choose the longer the dry to tack time.

Spike oil [specifically oil of spike lavendar] and also fir needle oil will provide good flowing in very small amounts. They extend dry to tack time, but will extend curing. Be careful with these as the varnish may appear dry on the surface but remain soft underneath as the solvent release is slow.

Kerosene, lamp oil and all of the high viscosity petroleum products. These will extend dry to tack time. They are very slow in solvent release. They do leave residual materials in the varnish film.

I would discourage adding any of these petroleum based solvents as part of the cooking process. They do not create the bond I have talked about. If you cook them in you just cook off the lower bp fractions....better to just use a higher bp mineral spirit and avoid the dangers.

on we go,

Joe

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Ernie,

Apples and oranges....Oil and resin [both properly prepared] heated to the correct temperature will melt together and become as stable mixture. Oil + resin + turpentine, properly prepared, cooked together correctly become a different material with properties which are different from those of the raw materials. An example: the IR of a properly made varnish is higher than any of its components. Knowing this, the varnish maker can adjust a variety of properties and still produce a stable and predictable varnish. When the turpentine component is eliminated the range of stable outcomes is very narrow.

Joe

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Like Joe said, varnish cooking is truly dangerous. That's the reason for the various temperature rules Jacob was complaining about.

I'm very afraid of a cooking fire, so I take lots of precautions, watch stiring and temperature closely, and always proceed as if the worst that could happen will happern.

Also as Joe said, I tend to cook small batches -- partly to keep the risks more managable.

I keep my cooking very simple. First I make a rosin by driving off the volatiles from Larch Balsam. Then I carefully cook together sun thickened linseed, mastic, and my 'Venice Rosin'. I do the thread test and that's it. I keep cooking at as low temp and short time as will get the job done, because I don't want my varnish to color or go dark.

I don't use any spike or turp spirit or alcohol in my cooking. For one, thery more dangerous to heat. Second, you'll mostly just drive them off anyway. I just heat the oil first and slowly add the other ingredients in crushed/powdered form until they incorporate.

My varnish is super thick after cooking, but I thin durring the cool down with spike.

I'm inclined to believe that Marciana and similar old recipes are refering to rosins cooked out from balsams. To me that seems more natural and consistent to the period than any other explaination I've heard or can think of. Also, I tend to believe when those early text don't say "SPIRITS OF turpentine", then they don't mean "spirits" -- what we commonly mean when we say turpentine. I rather think they either meant the balsam or the rosin, depending on context. IMO

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David, When you say vernice rosin, are you referring to raw pine gum or the liquid larch rosin you just cooked?

That's something I have to cook for myself. I start with true Larch Balsam. 'Venice Turpentine' is generally supposed to be Larch Balsam, but most things sold as 'Venice Turp' aren't really. Very often they are common rosin reliquifid with thinner. Or often they are some larch balsam and some common rosin. So getting a good quality natural balsam is the main trick. Then you just cook off the volatile components until you have a rosin. To check, I put a drop of the cooking balsam in water and see how hard it gets. You should get something as solid and glassy as violin rosin.

Again, this is dangerous. You have to get the temp up high enough to drive off volatiles, which you see rising off like a white steam. At the same time, you don't want to get too hot. If the 'white steam' starts to darken your too hot and need to back off pronto. Also, as your cooking progresses, you need a higher and higher temperature to drive the remaining volatiles off.

COOKING is DANGEROUS!!!!! Even cooling your work off can get you in trouble. If you cool something suddenly, you may get violent and dangerous splatter. If you go to hot you might get fire. If you don't have good ventilation, the air around you might ignite.

So back to topic. 'Venice Rosin' is my shorthand for 'Larch Balsam' cooked down to rosin. You can get very related rosins from other balsams.

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regarding stringing. I put a drop of the cooking vanish into water. If they have not combined the drop spreads out, as they combine a more coherent drop forms. you can then touch the floating drop with your finger, shake off the excess water pinch your fingers together and spread them a thread of varnish should form between your spreading fingers.

nice discussion-will need more therapy now...... :wacko:

Oded

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OK...so to make a solvent free varnish either kind of oil is OK to use as long as it dries on it's own. Make sure the resin and oil are properly combined...(string test).

So then resin/oil ratios are what determine the open time. A lean varnish will tack sooner than a long-oil varnish...correct?

No. On a solvent free varnish, tack time or working time is determined by when the varnish starts to polymerize. Since it won't be thickening from solvent evaporation, the vanish will stay about the same until hours have passed, or until it's exposed to UV, if the varnish contains no dries.

If you start with a thick oil, there's a higher chance that the varnish will be too thick to apply without adding solvents. I wouldn't expect that thick or thin oil will change the working time very much, but it would change the viscosity of what you're working with.

I wouldn't expect that resin/oil ratios would change working time much either on a solvent free varnish. They would change many other properties, such as viscosity, but not working time so much. The oil will still take about the same time to polymerize (again with the caveat that something in the recipe isn't acting as a drier).

Hope that's making a little more sense.

David, please expand on this.

"Oh, oil/resin varnishes which aren't "bonded", but more like suspensions or colloids can work too... I suspect it's more along the lines of what Strad used..".

Strad varnish appears not to have "self-leveled" very well. That could be a clue that the varnish was a mixture, as opposed to the components being chemically combined, or it could be a clue that it was such a high resin/oil ratio that whatever solvents were used were gone before it had time to flow. Once you get the resin proportion really high, you end up with something pretty thick (probably not brushable) until you add a solvent. Once the solvent is gone, it might even seem semi-dry, even though polymerization of the oil hasn't happened yet and it is not yet "chemically dry".

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or it could be a clue that it was such a high resin/oil ratio that whatever solvents were used were gone before it had time to flow.

In the Stradivari Varnish book, Stefan-Peter Greiner mentions a weight ratio of approximately 20 parts oil to 80 parts resin. He then saying the varnish is considered a lean oil varnish due to its oil to resin ratio of 1:4.

Cheers, Peter

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Well Ernie, in the thread I had started a while back my contention (based on a quote from William Fulton) that "pure gum spirits" dates from the second half of the 1700's was never properly addressed.

The Naval Stores Acts for English Commerce is discussed here:

http://www.jstor.org/discover/10.2307/2191724?uid=3739840&uid=2129&uid=2&uid=70&uid=4&uid=3739256&sid=21101313486267

This is an old book. Notice that the new world was the source of most of the turpentine etc. The act was to make uniform the various substances because of their importance to the use in sailing ships. After a trip from the Americas to Italy, turpentine would have thickened a good deal. This might make a Fulton-type resin automatic.

Or the oldsters could have gotten terpene materials from other, local trees. Larch turpentine etc. Anybody who wants to make varnish from tree saps certainly has a lot of choices.

By the way, thinners such as mineral spirits can be added to a cook as it cools, as David Burgess suggested. Maybe it is misleading to speak of "solvents." I have found xylene to be one of the most efficient cutters of viscosity that does not dilute an oil varnish very much.

For adjusting the oil length, one method is to make a short oil version and a long oil version. Usually, these can be mixed with no precipitations.

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Hmmmm....Not really. Here is an example...Which will dry faster? a 10:1 varnish (10 parts resin) or a 1:1 varnish. If you melt some colophony in a pan and dip a posicle stick in and remove it. it will have have zero open time because of having zero oil. So the the higher the resin ratio the quicker it will tack if we use identical oil and make several batches. A 10:1 ratio (10 resin 1 oil) should certainly have less open time than a 1:1 varnish...not because of the type of oil but because of a higher resin count.

So now as I see it... the ratio of resin is what determines the open time more or less. Further adjustments can be made using different types of oil.

I'll disagree. With a solventless varnish, the "open time" would depend on when the oil goes into the first phases of polymerization, which would be roughly the same regardless of the oil/resin ratio (probably at least several hours, barring driers once again). Its properties would remain largely unchanged until that reaction starts to occur.

Perhaps you're describing a scenario where the varnish isn't brushable in the first place. To me, that's not an issue related to "open time", any more than "open time" would apply to hard granulated glue, or unheated glue in a gel state. But I suppose you could call that an open time of zero if you found that description useful somehow.

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The Naval Stores Acts for English Commerce is discussed here:

http://www.jstor.org...=21101313486267

This is an old book. Notice that the new world was the source of most of the turpentine etc. The act was to make uniform the various substances because of their importance to the use in sailing ships. After a trip from the Americas to Italy, turpentine would have thickened a good deal. This might make a Fulton-type resin automatic.

Or the oldsters could have gotten terpene materials from other, local trees. Larch turpentine etc. Anybody who wants to make varnish from tree saps certainly has a lot of choices.

By the way, thinners such as mineral spirits can be added to a cook as it cools, as David Burgess suggested. Maybe it is misleading to speak of "solvents." I have found xylene to be one of the most efficient cutters of viscosity that does not dilute an oil varnish very much.

For adjusting the oil length, one method is to make a short oil version and a long oil version. Usually, these can be mixed with no precipitations.

Thank you for the link, very interesting, the trade by the Portuguese, Spaniards, British from the Americas+Africa+Indias+China at the time is very interesting, the more I read the books of the time, the more it seems that there was lots of stuff available, the many italian books on chemistry, pharmacy, liquor, geography, botany etc. which contain varnish recipes also mention spirito di trementina, olio of spike, olio di sasso (rock), petrolio and many others, some people who where making medicinal balsams, and had exotic high quality ingredients and retorts, where also cooking varnish. The recipe for shellac was diffused throughout Europe in the mid 1600's because of a book on China. Maybe some methods of the cremonese dudes are printed in a geography, or botany book.

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The Naval Stores Acts for English Commerce is discussed here:

http://www.jstor.org...=21101313486267

This is an old book. Notice that the new world was the source of most of the turpentine etc. The act was to make uniform the various substances because of their importance to the use in sailing ships. After a trip from the Americas to Italy, turpentine would have thickened a good deal. This might make a Fulton-type resin automatic.

Or the oldsters could have gotten terpene materials from other, local trees. Larch turpentine etc. Anybody who wants to make varnish from tree saps certainly has a lot of choices.

By the way, thinners such as mineral spirits can be added to a cook as it cools, as David Burgess suggested. Maybe it is misleading to speak of "solvents." I have found xylene to be one of the most efficient cutters of viscosity that does not dilute an oil varnish very much.

For adjusting the oil length, one method is to make a short oil version and a long oil version. Usually, these can be mixed with no precipitations.

distillation was known by and practiced by the ancient Greeks. They would place a fleece with the fur side down over a pot of cooking sap, the volatiles would condense on the fur and they would then wring out the distillate.

From my reading the end of the 1500's beginning of the 1600's was the period when distillation became more common and distillates of both botanicals and alcohols became widely available.

Oded

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From my reading the end of the 1500's beginning of the 1600's was the period when distillation became more common and distillates of both botanicals and alcohols became widely available.

Oded

Exactly! This makes distillate dependant processes less likely for practices that are seen at the beginning of the Amati family's journey; but reasonably possible for processes that developed later.

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Seems like a lot of fuzzy chemistry here. If oil and resin react during cooking to produce a third compound, why would that compound be expected to dry like unreacted oil? And especially, why would that compound respond the same to pyrolysis GC as separate oil and resin? I've used pyrolysis GC and do not recommend it unless you know EXACTLY what is going on. For instance, some break down products never get to the detector.

For my own varnish I use pre-reacted resin and oil. Not traditional probably. But if I used a 4:1 resin to oil ratio it would be unworkable.

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