Just for the record:
here is the Ordnance Recipe circa 1810:
"Six ounces of lamp-black, three pints of spirits of turpentine, and three ounces of litharge to be put in after the lamp black and turpentine are well mixed; add one ounce of umber to give it a gloss, and one gallon bright varnish."
Litharge is prepared by exposing melted lead, at a high temperature, to a current of air from a pair of blast-bellows, which blows off the oxide formed on the surface of the metal into a recipient, where it solidifies in minute scales. It is a protoxide of lead, containing one equivalent of lead and one of oxygen.- obvious lead poisoning hazard- please note.