Recipes for Moulding and Casting an Arc
Fuller's-earth and plaster moulds, thin glass, brass wire, opaque distilled water, cast tin and varnish
The page turns from water to workshop recipes for making and casting a curved element Leonardo calls an 'arc,' with a slender curved shape drawn and lettered in the upper right margin. In the first note the arc a-b is of linden boiled in Greek pitch so damp will not warp it, the arc n-m is set with pounded brick and pitch by a hot iron, a black space is filled with carefully alembic-distilled opaque water introduced through a hole a and sealed with wax. Under 'To make the arc' he describes settling and drying fuller's earth into a round bar of even thickness, polishing it, impressing it in fine plaster, then in very thin glass (written reversed), sheathing it, and edging it with fine brass wire before filling and sealing. A final section 'On casting the arc' calls for four arcs of four different bores at equal size, cast in tin as a plate, then turned and varnished; a marginal note recommends Gaeta soap with white wax, or fuller's earth with olive oil made hard.
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Casting the arc in tin
One must make arcs of four sorts, that is of four different capacities but equal in size. Take tin and cast it in a form to make a plate as described, then turn it and apply the varnish (written in reverse in the manuscript).
The mould of fuller's earth, plaster and wax
Settle and dry fuller's earth, shape it into a round bar of even thickness and polish it under its guide, then impress it in very fine plaster to obtain the arc's figure. Impress that in very thin glass, set it in its sheath after first impressing the plaster in wax, and edge the arc with fine brass wire.
A curved tube filled with opaque distilled water
The arc b-a is of linden boiled in Greek pitch so the damp will not warp it, and the arc n-m is stabilised with pounded brick and pitch by a hot iron. The black space is then filled through hole a with carefully alembic-distilled opaque water and sealed with wax.