FredN

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  1. 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?
  2. 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
  3. 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
  4. 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-
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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.
  11. 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
  12. Hi David, forgot insert, also sorry forgot how to reply and insertot attachment.
  13. 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
  14. Hi Dominik- I think the problem is adding the oil before cooking out the water from the resin. I think the temperature is high enough when you go to cook out the water you also make a calcium soap. Calcium soap is similar to a sodium soap with which you wash except it is barely water soluble, but it probably is hanging on to some water, or it is not soluble in the varnish mix and is congealing on to itself. The purpose of lime is simply to reduce the acidity of rosin, and really is not necessary for heat alone also does that, plus any metal you add. Jezzupe mentioned the possibility of gassing. Set up a bright light so that you can cast a shadow across the back, if the lumps sparkle they are gas filled. Solid ones usually don't. fred
  15. Hi Dominik, I've cooked rosin with a saturated solution of calcium hydroxide wetted into crushed resin with umber pigment, cooked to dry, then added the oil for a final cook and never experienced your problem. This makes me suspect the color coat or temperature of your cook. My cook is around 475oF for a few hours to where a drop on glass is no longer sticky when cool. Can you please describe the colored stuff and a little about cooking method. thanks