The Florentine gold-beaters used to have another way of casting,
which was called casting in the mortar,[122] for so was the furnace
called in which the casting was done. You take a number of bands of
clean iron[123] about half a finger thick and as broad as a thumb,
and weave them into a round shape, about one & one-third cubits high,
sometimes smaller, sometimes larger than this in accordance with the
quantity of the work you have to cast. It must be interlaced into a
domed shape to about two-thirds of its circumference, and from the
iron that remains over you make four legs on which the furnace is to
stand. Note that where these legs commence you must make a grating,
the openings of which are wide enough to allow of one finger and a
half being put through them, this serves as a base for the furnace.
And the furnace itself you construct by means of fashioning a cake
of earth mixed with cloth shearings,[124] the kind of earth that
glass-blowers use for their furnaces. Then you take a terra cotta
tile and lay it on the base of your furnace, and strew a little
ash over it. On this you stand your crucible filled with as much
silver as it can hold, and set to work very carefully, much as you
did in the previous method. You fill the furnace with coal, light
it and leave it to get red by itself, for thus left, the draught
will produce a tremendous fire, and you will cast better so than if
you made fire with your bellows. I must warn you too, to make your
crucibles out of clean iron, for earthenware ones would easily crack;
this iron should however be coated over inside & out with a paste of
clean ashes about half a finger in thickness, which must dry well
before the silver is put in. Some take for this solution clay mixed
with cloth parings, & the one is as good as the other. For the rest
you proceed with your casting just as I showed you above.
FOOTNOTES:
[122] _Fondere nel Mortaio_: _perhaps better, mortar casting_.
[123] _Lame di ferro stietto._
[124] _Cimatura._