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.
To Draw the Volute
From this as centre and one part as radius describe a circle. Within this circle draw a square, having for a diagonal the diameter of the circle. Bisect the sides of the square and draw the diameters by joining the points of bi-section. Divide these diameters of the square into six and these points will be the centres for the segments of circles which form the volute. Vertical and horizontal lines drawn from the centres will define the extent of each segment.
No. 161. Ionic Capital, with angular volutes.
For small scale drawings the volutes are drawn free-hand, but for larger working drawings it is necessary to use some method such as that given here.
The angle formed by the meeting of the ovolo and the volute is masked by a detail of anthemion form.