Steve Voigt

In my experience this is not correct. For example, if you add alizarin to rosin alone, you'll get no color change, just a bunch of alizarin at the bottom of the pot. Further, I assume you mean dyestuffs (e.g. madder, alizarin, walnut, etc.) and not pigment. Pigments are opaque. However, if you add a metal that functions as a mordant, you'll get color. Zinc will bind to many dyestuffs. Basically, you'll make a cooked zinc resinate, then add the dyestuff. I've done this with alizarin and can offer some tips if you want to go that route. Alizarin fixed to zinc is a very different color than alizarin fixed to aluminum. But making a cooked aluminum resinate is next to impossible. A cooked calcium/alizarin resinate is a lovely color. As soon as you add linseed oil, the color will vanish. However, if you are using straight resinate in turps, with no oil, it might work…you'd have to test it.

I think most people here would give a kidney to find a resin that turned a vibrant red after three hours of cooking. It’s a bit like asking for a unicorn. If you’ve found such a thing in Russia, I suggest redoubling your efforts to get it from there. Best of luck!

What a great story. Thanks so much for taking the time to write this up. Happy New Year!

Dave, I’d certainly like to hear more of your thoughts on this. What makes you say that turpentine resin is unstable? Also, what solvent(s) do you use? My experience: A drop of reasonably fresh turpentine on glass will completely evaporate. A drop that has been aged and has changed color will leave behind a resin that dries hard and appears stable to me. I’d love to know what has convinced you otherwise.

First of all, it sounds like you did almost everything right on your first try. Congratulations. The only thing you are missing is turpentine. I would expect the varnish you made to be almost solid at room temperature. The harder you cook the colophony, the thicker the final varnish will be, and the more turps you will need to add. I recommend taking the oil/resin mix off the hot plate and adding the turps while the mixture is hot, but not so hot as to cause the turps to boil. To be safe on your first try, add the turps at 150 C. Later, you can experiment with adding it hotter, if your risk tolerance allows. If you do that, make sure you have the cover handy—if turps starts to boil, putting the cover on will cut off oxygen. You can also use more oil, but then you are making a different varnish. It will have longer open time, but it will be softer and more flexible. The degree to which you process the oil also matters. I will guess that you used raw oil. If you washed it and heated it, your varnish would be even thicker, and you wouldn’t need to cook it for so long. You’re off to a good start—good luck and let us know how it goes.

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 !