Casting a terracotta mould for a pyramid base
Notes on a centring pivot and a beaten-terracotta mould, scalable to a pyramid of 100 to 112 braccia.
The right leaf (252r) carries two faint figures with letters and a note labelling one as a terracotta form (forma di terra cotta), accompanying a set of instructions for making a mould. The text describes fixing a needle-pivot at the exact centre of a template and pole so that the pole can be spun to test its centring, and building the base of a pyramid from beaten terracotta mixed with chopped horsehair to make it light and spongy so it need not be re-fired. The template itself is to be cast in copper or a lead-and-tin solder and then finished with emery. The left leaf (249v) is blank in this reproduction, and the figures on 252r show only faintly.
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Beaten-terracotta mould for the base
The base of the pyramid is first made with sand, but better of beaten terracotta mixed with chopped horsehair so that it is spongy; this serves as the mould and needs no re-firing. Two alike are to be made, with a chosen thickness placed in the middle to keep it light, formed before the clay is fired and then redone after firing for greater accuracy. The template is cast in copper or in a lead-and-tin solder and finished with emery.
Centring pivot a for truing the mould
A needle-pivot a is fixed in the middle of the template b c and in the middle of the thickness of the pole a d. To check the centring, the pole is spun quickly to see whether the point shifts its position; a tiny hole in the middle of the base of the pyramid receives and sheathes the needle.
Scaling one base to two pyramids
The same base could serve a pyramid of 112 braccia and one of 100, giving it two surfaces though at greater weight, being thin in the middle. The note advises first making a light one, and if it succeeds, then a version of 100 braccia and, on the reverse, one of a mile.