The mouldings of the Doric Impost are as follows:
At the top there is a fillet and a bold ovolo, below which there is a bead-moulding or small torus with fillet and two facias. The lower facia, which is of slight projection is one-fourth of the total height. The upper facia and fillet are half the remainder.
No. 168. Detail of Archivolts and Imposts.
Archivolt
The archivolt mouldings are in the Doric order, the same as those of the impost.
Ionic Impost
The total height of half a diameter may be divided into two, and the upper half sub-divided into three. Then the upper division will be the height of the top fillet and a reversa moulding; the second the height of a facia and the third an ovolo and small torus.
The lower half of the impost consists of two facias, the upper of which is broader than the lower.