No. 267. Boule Work. Period of Louis XVI.
Owing to technical limitations, modelling can only be broadly suggested; therefore forms should be generally in silhouette except when on a large scale.
When employed on walls and vaults, gold is frequently used in the backgrounds. This not only serves to define detail, but affords contrast to the general surface, the inevitable joints in the tessaræ adding also to the interest.
Byzantine Use of Marble
Associated with Mosaic decoration in the Byzantine Period was the employment of marble in shafts of columns and for lining walls by banding or slabbing, frequently quartered, so as to display the markings in reciprocal forms. Such marbles were chosen for figuring and colour, the former in its variety being an important factor in the surface interest.
Similar employment of slabs occurs in the treatment of floors, where contrast in colour is the chief consideration. It is sometimes associated with Mosaic of small tesseræ, also in marble, whereas that used on walls and in vaults was frequently of glass.
The foregoing is a broad summary of ornamental expression in the Flat, with the exception of Book Decoration.
Book Decoration
In Black and White, which is chiefly employed, the designs may be in tone or line with suggestion of rotundity or relief; or line decoratively employed, according to subject, or purely decorative.