De-Mystifying the Mix

The basic ingredients (clockwise, from left) are chalk, glue, linseed oil, and resin. Photo: Jonathan Thornton.

While various types of moldable composition date to the Italian Renaissance, architectural use of composition did not begin to flourish until the last quarter of the 18th century. During this period, many composition ornament makers in Europe and America supplied the public with complex sculptural decoration. Also, the overly complicated and often intentionally mysterious earlier recipes were now reported to be comprised of a few basic ingredients: animal glue, oil (usually linseed), a hard resin (pine rosin or pitch was cheapest), and a bulking or filling material, generally powdered chalk or whiting.

Compo: The Basic Ingredients

Chalk: Chalk is whiting in solid form. It is a type of white, soft limestone.

Glue: Before the invention of synthetic adhesives, glue meant animal or hide glue. This was made by boiling animal skins to extract a protein-collagen-in water, then condensing and drying the collagen until it was in solid form. A variety of types and grades were, and are still, available. Two are shown here.

Linseed oil: This is a yellowish drying oil obtained from flaxseed that is used in paint, varnish, printing ink, and linoleum; it is a key ingredient in composition ornament.

Resin: Resins are organic materials present in wood and exuded from various trees and shrubs. In unrefined form, they often consist of a mixture of solid natural polymers, oils, and volatile aromatic substances.

Compo mixes have been the subject of a good deal of variation and there has never been a set recipe, but the ornament manufacturers of the later 18th and early 19th centuries understood in general terms what their material was and what it could do. The advantages of the material were described by a prominent American maker, Robert Wellford, in his advertising broadside of 1801:

"A cheap substitute for wood carving has long been desirable for some situations, particularly enriched mouldings, etc., and various were the attempts to answer the purpose, the last and most successful is usually termed Composition Ornaments. It is a cement of solid and tenacious materials, which when properly incorporated and pressed into moulds, receives a fine relievo; in drying it becomes hard as stone, strong, and durable, so as to answer most effectually the general purpose of Wood Carving, and not so liable to chip. This discovery was rudely conducted for some time, owing to Carvers declining every connection with it, till, from its low price, it encroached so much upon their employment, that several embarked in this work, and by their superior talents, greatly improved it."