Steve Voigt

Mike, you’ve been making this claim for a long time. Can you provide any photographic evidence—an instrument or even just a sample of scrap wood—of this approach? I ask because it is completely contrary to my experience. I have never seen prolonged cooking of the varnish itself have the effect you are describing. All I have seen it produce is overcooked varnish. To me, making varnish is like making bread; if the prepatory steps (cooking the rosin and washing, heating, and/or blowing the oil) are done well , the final varnish cook is straightforward and fast. If they aren’t, then it’s like throwing yeast, water, and flour into a pan, sticking it in the oven, and expecting to get bread. With that said, I’m open minded and happy to be proven wrong. So if you have evidence that your method works, I’d like to see it.

The recipe you cite is a perfectly fine place to start. But if you are concerned about hardness, your plan to cook for a couple hours will not work. The longer and/or hotter you cook the rosin, the harder and faster drying the varnish will be. I recommend following the recipe. If you find the varnish is not hard enough, then next time increase either the cooking time or the temperature.

I was thinking more like Jedi mind trick. This is not the thread you are looking for.

First of all, Michelman did not cook his varnishes, he cold assembled them. Other people (especially @JacksonMaberry) do cook rosinates, but 8 hours? I’ve never of such a thing. Second thing: you are wasting your time trying to figure out a stoichiometric ratio for oil/resin. Stoichiometry is applicable to known quantities of defined substances, one of which is soluble in the other. “Oil” and “resin” are not such substances—they are complex, impure, and it is unclear to what extent they actually produce a true solution—much depends on the method of combination. Further, it has been known for literally centuries that oil and resin can be combined in almost any ratio. The relevant criteria is what working characteristics you want out of your varnish, not some half-baked chemistry justification. Which brings me to my final point: The information you seek will not be found in this thread. At all. Read the books that Jackson already recommended to you. They will tell you all you need to know about oil/resin ratios and much much more. The only thing they won’t help you with is the specifics of making violin varnishes, especially those that use rosin. For that, you can search the many threads here that discuss cooking colophony. You can read Michelman and Fulton. And then you can do the most important thing: pick a method and start exploring it. You started this thread with Hargrave’s varnish…that is as good a place as any to start. Look up Hargrave’s “making a double bass” (something like that) PDF and make the resin and varnish. Learn its characteristics. Then decide if you want to experiment further. This could take years. But posting endless questions here, and reading endless random chemistry articles, will not get you one step closer to your goal. Sorry if this sounds harsh, but it’s the truth.

Your experiments appear to show that the espresso method extracts more alizarin than I would have thought—congratulations. The only thing that gives me pause is that you said you “boiled” alcohol at 50 c. Alcohol boils at around 78 c, and if you try dissolving alizarin in alcohol (I have), you won’t get much until you actually reach a boil, bubbles and all. The soap looks promising. Your recipe has a very large excess of aluminum. I suggest consulting Michelman to get the proportions right. Fatty acids have a slightly lower molar mass than rosin acids—about 280 g/mol vs 302 g/mol—but FA soap also contains about 10% glycerine, so it’s basically a wash () on the weight. Put more simply, 10 g of oil, turned into soap, can be substituted for 10 g of rosin turned into K-rosinate. Hope that makes sense. For making varnish, you may have better luck cooking it into oil first, then combining the oil with resin. That’s been my experience, and it follows the pretty reliable chemical principle of like dissolves like.

Carry on. I look forward to reading your posts from the homeless encampment under the bridge, after you’ve burned down your house and shop.

You’re welcome!

No one would ever confuse me with the safety police, but I feel compelled to mention that this is insane. Cooking rosin or any other resin (or oil) at 400 C is asking for a fire. Not to mention totally unnecessary and counterproductive to the goal of making usable varnish. Be smart, people.

The company was founded by Joe Robson, who makes violin varnishes and occasionally posts here. And yes, he has stated that it’s not a violin varnish. They are minimalist finishes that are not intended to build a film. The claim that T & T finishes don’t dry or remain sticky/gummy is not uncommon, and is 100% user error. The directions on the can are quite clear and people who actually read and follow the directions will have no problems. I have had no problems. Anyone interested in knowing a bit more about Joe, T & T, and varnish making, might enjoy my interview with him, which starts here: https://blackdogswoodshop.blogspot.com/2022/09/interview-with-joe-robson-part-1.html?m=1

Calling @joerobson !

"Modern" varnishes are made with synthetic resins which are partly or wholly petrochemical in origin. Examples: Alkyd varnish is made by reacting fatty acids and glycerin with pthallic anhydride. That's the greenest of the bunch, although the manufacturing process used today is decidedly *not* green. Phenolic resins are nasty petrochemicals reacted to make a resin which is then cooked with oil. Polyurethane is similar but is often used without any oil, so it is a 100% petro finish. There are many more modern synthetic resins, e.g. epoxies. All of the above are thinned with petroleum solvents. There is a brand of "salad bowl finish" that is polyurethane dissolved in petroleum solvent, plus metal driers. Enjoy your arugula! Traditional varnishes use resins from trees, either fresh, partly fossilized, or fossilized; vegetable oil (usually linseed for violin sauce); and solvent--turpentine is traditional, but many others are possible, including "mineral" spirits, which are distilled from petroleum. I think some of the big commercial brands of violin use synthetic resin. Maybe John or Old Wood--I'm not sure. Check the websites. So those might be an option for you, if that's what you prefer.

Hi Andrew, sorry I missed this question earlier--I was distracted by the morass of debates over molecular structure and other irrelevancies. Hopefully we are getting back on track. It seems clear to me that the description (in John Smith) is for the color of the oil in a bottle, and not what it does to a piece of wood. It is easy to make oil a dark red color, but the color is fugitive and on wood or glass, it will look like any old oil. The easiest way to get red oil is to heat it, in a lidless pot, on a windy day. Another way, which gives a truly spectacular red, is to bubble the oil with a mini aquarium aerator for a few days, then heat it to say 250 C/1 hr. But again, the color of the oil doesn't transfer to wood. The ferrous sulfate, cooked into oil or resin or varnish, likely will give you a reddish brown (mostly brown) color on wood. By all means try it! Monitor wood samples you've finished with it closely for 150 years or so, and if they don't darken excessively, you are good to use it for the rest of your immortal life.

I'm gonna start calling you grumpy pants! I think we shouldn't lump all fusion methods together. There's a world of difference between adding small amounts of lime, and adding huge amounts of sulfates or chlorides (which, as you say, has become fashionable!). Varnish makers have been adding oxides, hydroxides, and acetates to to the pot for centuries…there's a track record. Sulfates and chlorides, not so much.

Zinc is divalent. So is calcium. They both combine in the ratio of 1 mole metal to 2 moles rosin acids. Aluminum is trivalent, so 1 mole aluminum to 3 moles rosin acids. If there is a metal in the universe that combines in the ratio 2:3, I haven't met it. Actually, I'm quite sure that's impossible with ionic bonds. Anyway, my point, which I think you agree with, is that the fusion method can lead to uncombined (that is, suspended) metal, which may (or may not) do unpredictable things. Iron is probably the least predictable at all metals, because even a PhD chemist can't tell you what will cause it to flip from ferrous to ferric (or the other way) in the chaotic, unpredictable environment that is a varnish pot. So, I don't use it. Except, as I said before, in the tiny quantities that leach out from a cast iron pot…

I feel your pain.