page twenty-three

The Kiln

Every other room on this site is made of arithmetic the site invented for itself. This one had to go and look something up. Today's number throws a pot and mixes a glaze to put on it out of real materials — feldspar, whiting, dolomite, talc, kaolin, a boron frit — works the recipe up into its Seger formula the way a glaze is actually worked up, adds the thermal expansion together oxide by oxide, and will not show you anything until the numbers land inside the limits for the cone it means to fire at. Then you are welcome to wreck it.

The pot

Drag the pot to turn it. Drag the handles on the profile to rethrow it — it is a surface of revolution, so the silhouette is the whole shape.

Left and right arrow keys walk to other days.

Form
Clay
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— · dealt from — · —

The glaze

Weight per cent into moles, the bases normalised to one, and the alumina and silica read off against that. This is the unity formula — the thing a glaze actually is, underneath whichever bag of powder you happened to reach for.

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Colour
Opacity
Surface
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Colour
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Silica : alumina
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Expansion
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Fit
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Melt
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Clay body
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Drafts
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The firing

A ramp to red heat, a slower one to the cone, twenty minutes held at the top, and then the part that matters: how fast it is allowed to come down. Fire a cone 10 glaze at cone 04 and watch it stay a dusty powder. Cool a zinc glaze slowly and watch crystals grow in it on the way down.

Cone
Air
Cooling
Then Peak, atmosphere and cooling rate are all read back out by the glaze.
Schedule
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Atmosphere
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Cooling
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How a glaze gets dealt

  1. 01

    Draft a recipe

    A skeleton suited to the cone — feldspar, a carbonate or two, kaolin, silica, and a boron frit at the low end, because nothing else will melt down there — is filled in with quantities drawn from the day's number.

  2. 02

    Work it up

    Each material's oxides are divided by their molecular weights to get moles, the bases are added up and everything is divided by that sum. What comes out is the same formula a glaze chemist would write down.

  3. 03

    Throw it out if it is wrong

    Alumina, silica, the ratio between them and the melt all have to land inside the box for that cone. If any of them misses, the draft is binned and another is written. You only ever see one that passed.

Three tables are doing the real work and none of them was invented here: fifteen raw materials with their oxide analyses, twenty oxides with their molecular weights, and a set of linear expansion factors. The unity formula, the silica-to-alumina ratio and the expansion figure are arithmetic on those, and the fit — glaze against clay body, crazing above, shivering below — falls out of the expansion difference. The melt model is the one honest fudge on the page: fluxing power weighed against alumina and silica and scaled by what the cone is worth. It behaves, but it is a heuristic, not chemistry, and it is only ever asked whether a glaze melts, not exactly how.

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The same date integer that drifts the field on the front page also seeds the Garden, writes the Chimes, deals the Lattice, names the town in the Almanac, scatters the Observatory, raises the coast in the Atlas, breeds the Menagerie, lights the star in the Orrery, invents the alphabet in the Codex, founds the countries in the Chronicle, designs the building in the Folly, cuts the gears in the Engine, threads the warp in the Loom, prices the goods in the Exchange, writes the rules in the Gambit, locks the doors in the Warren, hides the thief in the Inquest, cuts the gorge in the Span, writes the timetable in the Junction, enciphers the dispatch in the Bureau and cuts the letters in the Foundry — and here it mixes something that has to pass a chemistry check before anyone is allowed to look at it. The Foundry makes a thing you can read. This makes a thing you could drop.