To make a black liquid suitable for writing letters on opal glass, take 1/2 lb. of lampblack, dry. and place it on an iron plate, well saturate it with turpentine, then set tire to it and let it burn itself out. This will remove the grease - the non-drying oil - from the colour. Now grind it in hardl drying mastic varnish, and thin with turps. It would be better to give the letters two coats of thin colour rather than one thick coat.