Kilns and Firing Schedules Questions and Answers

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the mechanism. Quartz changes volume abruptly at 573 degrees in both directions, but on the way up the body is still weak and open and can accommodate the movement. On the way down it is a rigid, fully bonded ceramic, so the same volume change generates stress it cannot relieve. That is why firing schedules slow markedly through 573 degrees on cooling.

Answer: D

Correct answer: as cracks formed during cooling

Dunting is cracking caused by thermal or crystallographic stress during cooling - most often from cooling too fast through the quartz inversion, or from a draught striking part of the ware. The cracks are typically clean and sharp with no glaze rounding, which distinguishes them from cracks that were present before the peak.

Answer: A

Cordierite, silicon carbide and mullite are common choices depending on the temperature and the load. Furniture is a substantial part of the mass heated in every cycle, so its weight is minimised as far as strength allows.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the whole argument. Kiln furniture rides through the cycle with the ware and absorbs heat in proportion to its mass, so a heavy setting can consume more fuel than the ware itself. Lightweight cordierite and silicon carbide supports exist for that reason, and the ratio of ware to furniture is a standard measure of how well a kiln is being loaded.

Answer: C

It is heated and cooled with every cycle and in some kilns weighs as much as the ware itself. Reducing its mass is one of the standard routes to lower fuel consumption in a kiln. Lighter furniture also allows faster cycles for the same reason.

Answer: D

Packing more ware raises output but can shield some pieces from the heat and give uneven firing. The setting is arranged so that gas can circulate to every piece rather than simply to fill the space. Uneven setting shows as uneven colour or vitrification in the load.

Answer: A

Correct answer: excess oxygen beyond that needed for combustion

An oxidising atmosphere holds more oxygen than combustion requires, so carbon burns out completely and metal oxides remain in their higher states - iron as red ferric oxide rather than grey ferrous. A reducing atmosphere starves the flame and produces carbon monoxide, which strips oxygen from those oxides and changes the fired colour entirely. The atmosphere is therefore a controlled variable, not merely a consequence.

Answer: B

Organic matter in the interior cannot oxidise if the surface seals before the carbon has burnt away. A longer oxidation hold at moderate temperature is the usual remedy. The defect is invisible until the piece is broken across.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the timing constraint. Carbon burns out over roughly 300 to 900 degrees and needs oxygen reaching it through open porosity. If the temperature rises far enough for vitrification to begin sealing the surface, the remaining carbon is trapped, and it later reacts or expands to give a black core or bloating. The hold gives the oxidation time to finish while the body is still permeable.

Answer: D

A higher peak seals the body sooner and makes matters worse, since the carbon is trapped earlier. The remedy is a longer oxidising hold at a lower temperature before vitrification begins. Firing hotter closes the surface sooner and traps more carbon.