From about 1880 to 195, signs exposed to the weather, such as street signs, were very often made from vitreous enamel baked onto a sheet steel base. Vitreous enamel is a tough, shiny surface coating which was used to coat, for example, cast-iron bathtubs, the interiors of kitchen stoves and cast-iron pots and pans.
Vitreous enamel is similar to the glazes used in pottery: it is a combination of finely ground glass, called frit, and metal oxides which, after being heated to around 800oC, form a smooth, scratch and chemical resistant layer when cooled. Vitreous enamel is unaffected by ultra-violet light, so it is virtually fade-free, but, like glass, it does crack and splinter when bent or struck, and the steel substrate can rust.
The first coat of enamel, called…
