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  1. I have no pictures of it but i am confident this would be in the top of possibilities from various exp's.and what I've learned. Simplicity alone is a good reason. Buy (Kremers) or make some litharge, dump it into linseed oil, heat and add lead until you get the color you want. They had no thermometers then and most likely various stages like rim foam, surface foam could have been used as temp indicators. On maple it is dichroic, and coats of varnish dry solidly in normal drying times. I have not tried top wood but i would expect same results. It is good to hear Richard Pope mention it is well accepted in teaching schools. fred
  2. This is something i did in Nov '18 regards an undercoat. This is known as Black Oil, or Maroger Medium or a variant of it can read more in an article at https://en.wikipedia.org/wiki/Jacques_Maroger . It seems this undercoat has a long history in oil painting arts and possibly adopted by instrument makers for its bright yellow color and possibly more important, to assure the varnish will dry.. Anyone who has made a varnish that top dried is familiar this problem creates, staying sticky.. At 2:40 started heating 15 g boiled linseed oil . At 2:46 temp is 400F, no movement,clear color, no smoke At 415F light smoke started. At 2:51 temp is 535F, light smoke, quiet, no rim foam. At 2:53 temp is 561F , added 1 P litharge (P stands as an estimate of volume equal to a pea), Turned gold/black, still clear, added another P litharge, turned slight yellow gloss,- At 585F added 1P- At 2:58 1/4 inch of pink rim foam present, no islands ( bits of foam running to edge), turning darker gold (600F). Added 2P more litharge to a total of 5P lead. Color in jar is black, spread out on wood is bright transparent yellow. Dries in less than a day
  3. Hi Mike-It could be the Congo copal I sent to you years ago hoping to get other members to know how to make that type of varnish. Not easy. I lost my interest when I started to experiment with rosin. To my knowledge no researcher has found copal resins in Cremona varnishes, which is interesting for it could have been a common commodity in some households for it was the only weatherproof coating they had at that time for horse carriages, etc. Hope all is well and those Strads just keep coming. I stuffed my bank box with Canadian dollars, out of the dollar. Bad move?
  4. Hi Door Mouse, from my experience getting close to the cook becoming insoluble is optimal, but it is the oil that becomes insoluble in the mix. I've never had rosin by itself become insoluble. Appreciate any description on procedures that create this condition. fred
  5. Hi Giovanni- very knowledgeable response; I'm curious to know the procedure where rosin becomes insoluble in oil. I've made many runs and never experienced that. fred
  6. Hi Joe, thanks, I guess I should have added this varnish takes around 5-7 coats, ca 2 per day, some wet pumicing or super light sanding near the end coats for nits. Apologize for the misspelling-
  7. A 2oil:3resin is ok in making a cooked varnish. In one of your runs, increase temp until you have a little surface foam, stay there until it starts to reduce which indicates your oil has been heat bodied and your varnish will air body when you spread it out in a film. Add turp until a drip will almost want to make a doughnut. If a smear on the lid of the jar forms a ridge along its edge you know you have god surface tension to level the surface.
  8. Interesting that grapeseed oil is hardly mentioned in older literature even though its drying qualities are not much different than linseed oil. Certainly must have been available.
  9. I recall I used to carefully pick a can from the back of the row, and if not disturbed for a length of time they are well separated. Maybe chilling (freezing?) might help.
  10. Taylor makes a thermometer ( or used to) that is around 6" long that goes up ca 600F. It is on a band of metal with markings that you can remove ( very very carefully, the therm is expensive) and wrap it to a grooved stick long enough to keep fingers high. Wrap wire at 50 degree markings, which is accurate enough, Strad says. Wire has to be corrosion resistant, like stainless, for rosin is very corrosive if that is your resin.
  11. Not important, but I think the term linoxyn refers to a brief peroxide stage of linseed oil when it is transiting from taking up oxygen to the next phase. I'll keep looking, and apologize if I'm wrong. I came across this site, http://www,patriciabennettstudio.com/Materials.htm, discusses a substance called Black Oil which is cooking litharge and oil, adding equal amounts mastic resin. It supposedly was originated by early Italian painters as undercoat and is why their paintings excelled. It is called Black Oil but it is red when thinned. It is easy to make. It is interesting that modifications to it by various artist such as adding beeswax is similar to violin varnish additives. Apologize for being off topic.
  12. Bubbling air into the turp is the typical way to speed up changing the turpentine into alcohols. It is no longer turpentine but a very strong solvent with reduced vapor pressures, so it does not vaporize as fast as turp. Cooking out the water is the problem, Many believe there is an exothermic reaction when the temperature is around that of boiling water that will cause an explosion. I believe it is the generation of steam. To prevent this use a utensil with a wide opening and a shallow depth to the liquid. Also, break up an old porcelain cup into pieces to cover much of the bottom. They act as boiling chips to prevent large masses of steam to develop. David Burgess will add further information.
  13. Dominic- you won't know the cause until you repeat the making and cook out all the water out of the resin before you add oil. Use a commercial Boiled oil, not raw to shorten the cook time to string, then use some good oil when you've got out the problems. I would not smear a colorant on the inst, if it is a raw oil mixed with the pigment it would take weeks? for it to dry laying on the bench. If you want to color the varnish squeeze around 1/4 inch or more of Ochre, Sienna or Umber into the mix, cook around 350oF ( ca 10 hrs) to an almost tackless bead on glass or to a 12-14 inch string ( when a drip on glass makes a round dome the cook is done). A drip on glass shows the bead keeps getting darker over time, and has to be dead black at the end to have good color when thinned. My varnish mix is around 12g oil to 15g resin. You lose around 15% resin, so the ratio is ca !:1 at the end. Add lime before oil is added, heat resin to ca 400oF and add 5-6% lime, cook for a few minutes and then add oil. As some have mentioned, have your lucky charm nearby. fred
  14. Hi David, forgot insert, also sorry forgot how to reply and insertot attachment.
  15. Hi David, regards heat reducing acidity, hardening- I've attached a small statement on heating rosin. The chapter has more on the subject but you have to be an organic chemist to understand it. Just heating to melt and exposing to air increases melting point. fred
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