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Oh, caution! And let there be caution in these operations. For some vessels are wooden, and some are of lead or copper; some are of unglazed earth, and some are glazed, all of which will be shown later in the instructions for the operations.

Method for furnaces

¶ There are many types of furnaces: some are the "philosophical furnace," some are for sublimation The process of turning a solid into vapor to purify it, some for distillation Heating a liquid to create vapor that is then condensed back into liquid, and some for glazing. The philosophical furnace should be built near a wall where the wind cannot strike it, or it should stand away from the wall at the distance of an arm's length, in this manner: Let a pit be made in the earth to a depth the size of two spans A span (spanna) is an ancient unit of length, roughly 9 inches or the width of a human hand with fingers spread, which is lined with "master's clay" original: "argilla magistri". With this clay, build a wall in a circle. Take simple clay and add to four parts one part of good potter’s clay, mixing it very well, and add a little sand; with this mixture, build the wall. The pit should be two feet high and one span in thickness; let it dry. Then, you must have a grate original: "rota" (literally "wheel"), here referring to a perforated circular tray that holds the fuel or the vessel made of good potter's clay that can withstand a strong fire. It should be perforated everywhere with small holes so that [ash] can easily fall down below. In the earth, let a passage be made between the pit and the wall, one span wide, before the grate is placed on top; and let there be an arch where the pit is open toward the wall, about one span wide, and the passage must be lined with clay which is placed below, from which the expansion

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of the holes should be. Then, let a wall be built above the grate to the height of an arm and a thickness of a span, in the manner of a kiln. It should have an opening like a kiln's mouth. Let there be a lid [or cover] fitted to the top of the wall that has, through its thickness, four or six small holes the width of fingers; these are the vents of the furnace. ¶ Furthermore, it should be known that upon the grate one must place a tripod made of good potter's clay, upon which the calcining vessels Vessels used for calcination, the process of heating a substance to high temperatures to drive off volatile matter should be placed, with charcoal underneath. ¶

Method for a sublimation furnace

The furnace for sublimation and the furnace for distillation are made in this way: Take the same clay as described for the philosophical furnace. Let a round wall be built upon the ground to a thickness of four fingers, a width of three palms, and a height of two spans. Let the grates and passages be made in all respects as described for the philosophical furnace. The difference, however, is this: the sublimation furnace and the distillation furnace are open at the top, and upon these openings the vessels should be placed on tripods suited for them, so that it can be observed whether the vapors are breathing in or out. And it should be noted that the distillation furnace ought to be wider at the top than at the bottom, and the sublimation furnace ought to be wider at the bottom than at the top. ¶ The glassmaking furnace should be made in a spacious place between walls; let stones be placed in the manner of walls and build the wall of them with clay that well

Method for a glassmaking furnace