This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
This may be effected by first coating the glass with lead, as is sometimes done to give a bright reflecting surface. Small flat pieces of glass are painted over on one side with chalk or colcothar and water, and then left to dry. They are placed with the coated side downwards on the bottom of a flat cast-iron tray about 1 ft. square, surrounded by a vertical border of 1 to 1 1/2 in., and are gradually heated in a large muffle to a temperature somewhat above the melting-point of lead. The tray is withdrawn, and melted lead is immediately poured into it sufficient to cover the glass, which is held down by pieces of wire. A slightly oscillating movement is given to the tray, so as to cause the molten lead to flow gently backwards and forwards. After a short time, a plug is taken out of the corner of the tray, which is tilted to let the lead run off as completely as possible. The pieces of glass will now be covered with a firmly-adherent film of lead. The lead employed should be of good quality; and in order to prevent it from becoming mixed with any oxide which may have formed on its surface, the tray is provided with a gutter-like arrangement, leaving only a slit for the passage of the lead. The tray is suspended at one end by a chain, and held by tongs at the other.
Glass buttons thus backed with a lead coating have their shanks soldered on (Dr. Percy). Solder may also be made to adhere to glass by first coating the glass surface with amalgam.