Mix with white-lead, boiled oil or varnish, and a small quantity of driers (no turps, which hardens for the time, being a volatile oil, and therefore objectionable in this case); paint this over the glass thinly, and stipple it. If you have not a proper brush, make a large pledget of cotton wool or tow, cover it with a clean bit of linen rag, and quickly dab it over the paint.