Scagliola derives its name from the Italian word for scale or shell a reference to the form of selenite that was ground and calcined to make plaster of Paris. Selenite is also known as “moonstone” for its opalescent glow. This is the origin of an alternate name for scagliola, “La Pietra di la Luna”.
When plaster is mixed with a diluted solution of hide glue and water, and colored with lime-proof mineral pigments, a variegated material similar to that of quarried marble is created. A slice or section of this material, when hardened, can be polished to a high sheen.
“Stucco marmo” or marbled stucco, is the term used when referring to scagliola executed on a large scale, for walls and columns.
Over the centuries, the process of making scagliola has been shrouded in mystery; a closely-guarded secret among protective craftsmen. To this day, craftsmen and restorers refuse to offer classes. But, the veil is lifting. Since I first studied in 1997, I have actively tried to document the process and spread the finer points of the technique to dozens of students worldwide. I am currently working on a “cookbook” of the process, with detailed formulas laying out the process. In the photo gallery on the right are some photos from the fabrication of an inlaid bar.
So the secret isn't very secret after all: simple materials--plaster of Paris, hide glue, powdered pigments--with a generous amount of diligent polishing and good design equal great results.