The Ornamental Plaster Trade

Shop Personnel. As builders and architects were hired by an increasingly affluent clientele, ornamental plaster shops developed from the single artisan operations of the 18th century into the complex establishments of the early 20th century. American plaster studios employed immigrant and, later, native craftsmen. Plasterers' guilds were in existence in Philadelphia in the 1790s. In 1864, a plasterers' union was organized in the United States with members from the British Isles whose work there had been limited to palaces and churches. English and European craftsmen came to America where the demand for their skills had increased by the decade, offering them the unparalleled opportunity to open their own shops. Over the years, plaster elements became so popular in decorating interior spaces that a major industry was established. By the 1880s, catalogs were available from which property owners could select ornamentation for their splendid new buildings.

Methods of Production. Historically, ornamental plasterwork has been produced in two ways: it would be run in place (or on a bench) at the site; or cast in molds in a workshop. Plain plaster molding without surface ornamentation was usually created directly on the wall, or run on a flat surface such as a plasterer's workbench and attached to the wall after it set. Ornament such as coffering for ceilings, centers for light fixtures (medallions), brackets, dentils, or columns were cast in hide glue (gelatin) or plaster molds in an offsite shop, often in more than one piece, then assembled and installed in the building.

Mitering a plain-run cornice requires great dexterity using the miter rod. Photo: Old-House Journal.

Decorative Plaster Forms--Cornices, Medallions, Coffers. Three decorative plaster forms in particular--the cornice, the ceiling medallion, and the coffered ceiling--historically comprised much of the ornamental plasterers' business. These forms appear individually or in combination from the 18th to 20th century, irrespective of stylistic changes.

For example, an elaborate parlor cornice consisted of plain moldings made of gypsum and lime run atop temporary lattice strips around the room. Tooling for plain-run moldings called for a sheet metal template of the molding profile mounted on a wooden "horse". Mitering was accomplished using a plaster and lime putty gauge (mix) tooled with miter rods at the joints. Decorative "enrichments" such as leaves, egg and dart moldings, and bead and reel units were cast in the shop and applied to the plain runs using plaster as an adhesive. Painting, glazing, and even gilding followed. Large houses often had plain run cornices on the upper floors which were not used for entertaining; modest houses also boasted cornice work without cast enrichment.