Mix and grind fine as possible on water cooled mill:
4 pounds finest jet carbon gas black;
bodied drying linseed oil;
color grinders' japan;
Add enough good rubbing varnish to the above to make 40 pounds of material, which thin with 4 gallons gum spirits of turpentine and 5 gallons good turpentine substitute. Result 13 1/2 gallons. If selling price permits doing so, omit the substitute turps and use 9 gallons gum spirits.