Shared controls

Start of firing

The techie stuff

Each kiln runs an independent exploratory vertical slice of a round electric kiln. The default is 25 kW available element power and an approximately 71 × 69 cm inner chamber. In AB Comparison, shared playback advances both kilns; in Single kiln mode, only the selected kiln advances and the other stays hidden. Loads, programmes, available power and manual probes belong to each kiln. Previous and Next align both models at the same programme segment's target or hold end in comparison mode, even when they reach that event at different elapsed times. This 2D slice cannot reproduce all airflow and radiation paths.

How the model works

The grid gives air, brick, shelves, pots and elements different heat capacities. Neighbouring cells exchange heat. Early in the firing, warm air rises strongly through open vertical passages, while two closed circulation paths carry it up the sides, across the top and back towards the lower chamber. An additional side bypass represents rising air travelling around shelves in front of and behind this vertical slice. These transfers conserve energy and weaken as radiation becomes dominant.

Element radiation heats the exposed surfaces of pots and shelves. Hot brick, furniture and ware then exchange radiation across visible air paths. A pot also has a separate interior-clay temperature for each wall cell: its surface first receives heat from the chamber, then conducts it into the body and along connected clay cells of the same pot. This internal heat store slows the ware and can continue to warm during a thermocouple-controlled hold. Shelves and posts store heat and conduct it along the solid. Heat in the wall passes through inner refractory and outer insulation before reaching surfaces exposed to the room. A hold can reduce the spread without making every place identical.

The ramp/hold controller reads a simulated thermocouple near the side wall. It requests a duty cycle, while the element relays switch on and off in 40-second cycles. Each ramp's requested temperature advances at its programmed rate, but its hold and the next segment begin only after the thermocouple actually reaches the target. A 9999°C/h heating ramp requests full available power; it does not impose that rate on the kiln. Programmed cooling segments likewise wait for the measured drop. After the final row, the controller switches off the elements and the simulation continues cooling naturally until the kiln thermocouple reaches 200°C. This final cooling is separate from the programme and is included in the graph and timeline. Available power is an editable kW value that changes element energy only: it does not change heat transfer, losses or controller settings. Low power can lengthen a firing or prevent it reaching a target.

Reading the heat map

Absolute temperature uses the same 0–1300°C colour scale throughout the firing, so colours at different times can be compared directly. Spatial difference rescales to the current chamber range, excluding the coils from its endpoints, to reveal smaller gradients at a chosen moment. Change in last 30 min shows the actual change in each cell over the preceding thirty simulated minutes: blue cooled, orange warmed and pale cells changed little. In the first thirty minutes it compares with the start. It displays calculated temperature changes, not animated airflow.

Pot interiors are coloured by their modelled body temperatures; the thin coloured edges indicate exposed surface temperature. Click a pot to inspect its current surface and interior-clay temperatures below the graph.

The central chamber spread is the difference between the 10th and 90th percentile temperatures of central air, shelves and pot interiors. It excludes element pixels and the brick shell. Its dotted graph line uses the right-hand °C axis; the kiln and manual TC lines use the left. Shared graph zoom changes both temperature axes together and gently zooms toward the right end of each firing timeline. A faint dotted guide shows 100°C below each programme’s highest target; it is a reference temperature, not a cone or heatwork calculation. Its readout compares the current spread with the start of a hold, and the event log records the spread at each hold's end. A faster firing can widen this spread while a hold narrows it. The top and floor can still remain cooler as the elements cycle.

What to expect

Pattern	Model behaviour
Early firing	Buoyant air moves heat toward the upper chamber, above loaded lower regions.
Hot chamber	Radiation increasingly heats ware and shelves; the interior becomes more even while the boundaries can still lag.
Boundaries	Both the lid and the floor can remain cooler than central positions.
Load	A dense stack stores more heat and shields some surfaces, so ware warms later.

The capacities, view factors, two-layer clay approximation, wall losses and control gains are illustrative and have not been calibrated against your kiln logs or cone packs. A real mug's wall thickness, clay body and stacking geometry would change its lag.

Background: Orton's explanation of convection, radiation and conduction through ware.

Cone temperature equivalents · older chart basis

This chart uses older temperature equivalents for large Orton cones. The 60 and 150°C/h columns come from the historical references below. The 15°C/h column is an estimate: for each cone, the 2016 Orton self-supporting value has been adjusted by the difference between the older and newer 60°C/h values. Orton did not publish these estimated 15°C/h values for large cones. Heating rates refer to the last 100°C (180°F) of the firing.

Cone	°C · last 100°C			°F · last 180°F
Cone	15°C/h	60°C/h	150°C/h	27°F/h	108°F/h	270°F/h
022	—	585	600	—	1085	1112
021	—	602	614	—	1116	1137
020	—	625	635	—	1157	1175
019	646	668	683	1195	1234	1261
018	667	696	717	1233	1285	1323
017	694	727	747	1281	1341	1377
016	734	764	792	1353	1407	1458
015	749	790	804	1380	1454	1479
014	784	834	838	1443	1533	1540
013	839	869	852	1542	1596	1566
012	848	866	884	1558	1591	1623
011	868	886	894	1594	1627	1641
010	875	887	894	1607	1629	1641
09	902	915	923	1656	1679	1693
08	925	945	955	1697	1733	1751
07	959	973	984	1758	1783	1803
06	974	991	999	1785	1816	1830
05	1021	1031	1046	1870	1888	1915
04	1033	1050	1060	1891	1922	1940
03	1071	1086	1101	1960	1987	2014
02	1077	1101	1120	1971	2014	2048
01	1091	1117	1137	1996	2043	2079
1	1108	1136	1154	2026	2077	2109
2	1112	1142	1162	2034	2088	2124
3	1115	1152	1168	2039	2106	2134
4	1147	1168	1186	2097	2134	2167
5	1150	1177	1196	2102	2151	2185
6	1164	1201	1222	2127	2194	2232
7	1177	1215	1240	2151	2219	2264
8	1198	1236	1263	2188	2257	2305
9	1224	1260	1280	2235	2300	2336
10	1251	1285	1305	2284	2345	2381
11	1272	1294	1315	2322	2361	2399
12	1285	1306	1326	2345	2383	2419
13	1300	1321	1346	2372	2410	2455
14 ‡	1374	1388	1366	2505	2530	2491

— Orton’s 2016 chart gives no 15°C/h value for cones 022–020, so this table makes no estimate for them. ‡ The older chart lists cone 14 at 1388°C (60°C/h) and 1366°C (150°C/h); the unusual reversal is retained here. Fahrenheit temperatures are converted from the displayed Celsius values and rounded to whole degrees, so some differ by 1°F from the historical printed values. Actual bending depends on mounting height, atmosphere and firing conditions. Use witness cones to assess a firing.

Sources: a 2010 Euclid catalogue reproduction and “Temperature Equivalents for Orton Standard Pyrometric Cones, as Determined at the National Bureau of Standards”, reproduced in an older, unidentified book; Orton’s 2016 cone temperature equivalents ↗. This table is a historical teaching reference; the simulator does not use it to compute cone bending.

Glazy Plugins for the Lazy and Impatient

Some JavaScript plugins (bookmarklets) to tickle your fancy and automate/augment a few bits on glazy.org

Saving a triaxial blend (or any)… oh SO many names and button clicks!

Glazy – Blend Photo Manager

WHY do I have to set cone 6, neutral/oxidation, blah blah blah on EACH recipe INDIVIDUALLY?!?

A little one just for when I mix up a batch…

And also some stuff for printing…

Kiln heat simulator

Shared controls

The techie stuff

How the model works

Reading the heat map

What to expect

Cone temperature equivalents · older chart basis

Load kiln

Firing programme

Studio & Gallery

Hours

Contact