Shellac

/Shellac
Shellac 2016-12-06T05:35:21+00:00

Shellac

Shellac Union Cases Ambrotype in shellac frame mineral filled shellac box
Tortoiseshell lined shellac snuff box shellac dish on wooden base Hand mirror Florence compound

Shellac has been used for centuries in lacquer form as a protective and decorative finish for wood and metals (not to be confused with Chinese lacquerwork that is based on resin from Rhus verniciflua trees). The lac insect is a plant parasite producing an exudate as a protective barrier against predators. Traditionally scraped off twigs with the eggs, larvae and pupae and insects, the shellac is cleaned and filtered to produce a hard, brittle thermoplastic material. This is used as the basis for sealing wax. 

In the nineteenth century many mixtures and compositions were based on shellac, the most successful being the American ones of Peck, Halvorson, and Critchlow. Wood powder was the filler mixed into the molten shellac to produce a composition or mixture capable of being moulded by heat and pressure. They made Union Cases to hold early daguerreotypes and ambrotypes. Over 1000 different Union Case designs are known, predominantly black in colour, although red brown and other dark shade examples exist. The moulded-in designs vary from the machine-made strictly geometric, through stylised floral to the pictorial, frequently based on established popular paintings. Sizes vary from 1/16th plate to the full plate 190 x 237 mm. Shellac slowly thermosets above 100 degrees C, and most shellac Union cases are largely no longer thermoplastic as the reaction continues even at room temperature. 

As photographic technology improved, so the requirement for folding cases diminished and conventional decorative ‘picture’ frames were produced. Many Union cases have the manufacturers’ name and patent details printed on paper and glued to the inside, behind the image, but very few have moulded in trade marks.

As the technology shifted to mineral filled shellac, trade names became more frequent, e.g. Smith’s Patent American Composition of solid back frames. Dressing table sets with brush and mirror backs in black shellac compositions (Diatite, etc.) are not uncommon, occasionally with patent numbers or dates moulded in. In England, Manton patented his composition and used it on black brooches of various designs.

Mineral filled shellac was the material used to make 78rpm records.