Repairing Historic Sign Materials

Porcelain Enamel. Porcelain enamel is among the most durable of materials used in signs.(8) Made of glass bonded onto metal (usually steel) at high temperatures, it keeps both its high gloss and its colors for decades. Since the surface of the sign is essentially glass, porcelain enamel is virtually maintenance free; dirt can be washed off with soap and water and other glass cleaners.

Porcelain enamel signs can be damaged by direct blows from stones and other sharp objects. If both the enamel surface and the undercoat are scratched, the metal surface can rust at the impact site. Because the bond between glass and metal is so strong, however, the rust does not "travel" behind the glass, and the rust is normally confined to localized areas. The sign edges can also rust if they were never enamelled. To treat the problem, clean the rust off carefully, and touchup the area with cold enamel (a type of epoxy used mostly in jewelry), or with enamel paints.

Dents in porcelain enamel signs should be left alone. Attempting to hammer them out risks further damage.

Goldleaf or Gilding. Goldleaf or gilding is both elegant and durable. These properties made it among the most popular sign materials in the nineteenth and early twentieth centuries. Surface-gilded signs (for example, gilded raised letters or symbols found on the exterior) typically last about 40 years. Damage to these signs occurs from weather and abrasion. Damage to gilded signs on glass normally occurs when the protective coating applied over the gilding is removed by harsh cleaning chemicals or scratched by scrub brushes. The sign can then flake upon subsequent cleanings.

Historic gilded signs can be repaired, typically by regilding damaged areas. An oil size is painted on the surface. The gold leaf is applied when the surface has become sufficiently "tacky." Similarly, historic "reverse on glass" goldleaf signs can be repaired--by experts. A sample of the flaking sign is first taken to determine its composition. Reverse on glass signs use goldleaf ranging from 12 to 23 karats. The gold is alloyed with copper and silver in varying amounts for differences in color. (Surface gilding--on raised letters, picture frames and statehouse domes--uses 23 karat gold. Pure gold, 24 karat, is too soft to use in such applications.) The damaged portions of the sign are then regilded in the same manner as they were done historically: the inside surface of the glass is coated with a gelatin; gold leaves about three inches square are then spread over the area. The new letter or design is then drawn in reverse on the new leaf, and coated with a backing paint (normally a chrome yellow). With the new design thus sealed, the rest of the leaf is removed. The sign is then sealed with a clear, water-resistant varnish.