BLACK OIL is made of purified raw linseed oil cooked with red lead and adding mastic.
Cold pressed raw Linseed Oil - 96.5g Mastic - 30g Pbo - 4g
This comes out to visually about 1/2 cup oil, a handful of crystals, and about a 1/4 tsp of PbO. Using a Corningware or some other such porcelain container and a cooking thermometer reserved for this purpose, slowly heat the mixture. Whatever you do, do not let it smoke or boil.

The transformation should start taking place, turning the mixture from orange to the color of black coffee. Stir occasionally with a wooden spoon - NOT A METAL ONE. This is crucial. After the coffee color is reached, let it cook for one hour to make sure the change is complete. The PbO does not go into the air, there are no poisonous fumes, so don't worry about that. At this point I like to let the temperature down a bit, before I slowly add the mastic, stirring it in. 

There is a variation that skips the mastic and goes for 10g of beeswax, but I have never bothered to try it as I want the brilliance the mastic gives - besides you can always make a paste of wax and resin and add it later (I recommend adding some carnauba wax, it is harder than ordinary beeswax). Okay. Now that everything is cooked, you have Black Oil. Just forget about this for now,
you are not there yet, I don't know why anyone would want to paint with this as it is. Add 40-45% turpentine to the oil, damar and lead. This is very crucial - if it is exactly half, the transformation will not take place. Seal it tightly, and put it in the 'fridge overnight. Tell yourself what an alchemical magician you are (I'm only half kidding) as it will transform into Jelly.

When using this, use just a little, maybe about a third added to your tube paint should do the trick - if it is slick, you are adding too much. Not only will your paint look incredible, you will be able to blend like you've never done before, add beautiful thin layers, put in detail that will stay, not drip or run, and any layer you make will dry within 24 hrs! I also recommend using Titanium or Zinc white with this as well, flake white doesn't work well with it at all - it already has the lead in it.

Mastic would still be the preferred medium for Pictura Translucida as it yellows less than oil and is completely transparent.