Description of the Most Principal Mineral Ores

A woodcut illustration shows various components of assaying furnaces, including a low rectangular oven (A), a furnace on an octagonal base (B/C), and a taller furnace (E/K).

How the assaying furnaces should be arranged

When now this assaying furnace is thus far ready / let two small iron rods be made in equal length / that go through the holes / which are between the lower and upper mouth hole / and reach about a good cross-hand length out in front of the furnace / upon which the small plate can lie in front of the upper mouth hole / Then let a bottom plate be made / that is no thicker than from the small rod / to the bottom of the upper mouth hole / and be so wide / that it reaches a little over the iron rods / and from the bottom plate / to the sides taper / leaving a space of a good two fingers / Likewise there should also be as much space in the back of the furnace / so that the wind can go through it up into the furnace / and drive the fire. To this assaying furnace belong