Ionic Capital
The Ionic capital is half a diameter high, and is readily distinguished by its bolster-like form with voluted ends. This bolster is rectangular on plan, and measures laterally rather more than one and a half diameters, while from back to front it is slightly less than a diameter.
The shaft terminates in a cavetto curve, and is surmounted by a fillet, a small torus and an ovolo moulding, which is invariably decorated with egg and tongue detail. These mouldings all conform to the circular plan of the shaft. On the ovolo rests the voluted bolster.
The abacus, which is square on plan, consists of a reversa moulding and fillet.
From the top of the abacus to the base of the ovolo the height is about a third of a diameter, and one-fourth of this height will give the height of the abacus.
The centre or eye of the volute can readily be found by dropping a perpendicular from the lower edge of the reversa to intersect the horizontal line defining the base of the ovolo. This point of intersection is the required centre.