On Architecture

3. Having thus set the vaultings in their places and interwoven them, apply the rendering coat to their lower surface; then lay on the sand mortar, and afterwards polish it off with the powdered marble. After the vaultings have been polished, set the impost mouldings directly beneath them. These obviously ought to be made extremely slender and delicate, for when they are large, their weight carries them down, and they cannot support themselves. Gypsum should by no means be used in their composition, but powdered marble should be laid on uniformly, lest gypsum, by setting too quickly should keep the work from drying uniformly. We must also beware of the ancients' scheme for vaultings; for in their mouldings the soffits overhang very heavily, and are dangerous.

4. Some mouldings are flat, others in relief. In rooms where there has to be a fire or a good many lights, they should be flat, so that they can be wiped off more easily. In summer apartments and in exedrae where there is no smoke nor soot to hurt them, they should be made in relief. It is always the case that stucco, in the pride of its dazzling white, gathers smoke not only from its own house but also from others.