An astragal is a moulding of a semi-circular profile; its construction is so simple that it would be unnecessary to say any thing concerning it. Fig. 1.
There are two kinds of beads, one is called a cocked bead, when it projects beyond the surface to which it is attached, see Fig. 2; and the other is called a sunk bead, when the sinking is depressed beneath the surface of the material to which it is attached, that is, when the most prominent part of the bead is in the same surface with that of the material, Fig. 3.
A torus in architecture is a moulding of the same profile as a bead; the only difference is, when the two are combined in the same piece of work, the torus is of greater magnitude, as Fig. 4; in Joinery the torus is always accompanied with a fillet. Fig. 5. single torus moulding.
The Roman ovolo or quarter round, as called by joiners, is the quadrant of a circle, Fig. 6. When the projection and height are unequal, as in Fig. 7, take the height B C, and from the point B describe an arc at C, and with the same radius from A, describe another arc cutting the former at D, with the distance A D or D B describe the profile A B. This is generally accompanied with fillets above and below, as in Fig. 7.
The cavetto is a concave moulding, the regular profile of which is the quadrant of a circle, Fig. 8; its description is the same as the ovolo.
Check back for Figs. 9-12, the scotia, ogee, cima-recta cima-reversa
From Peter Nicholson’s “Mechanic’s Companion”