Orton Foundation Firing Tips: Finding the Bending Face

When mounting cones in clay pats or commercial cone holders, sometimes the question arises concerning the direction the cones should bend, which way the number should be facing and how to determine the mounting angle.

Hold cone vertically and then set its base down on a flat surface. While the cone is still being held, you will observe that it is leaning at an 8 degree angle. Now, let go of the cone...it will fall in the direction that it will bend and the face of the cone that is against the flat surface is known as the "bending face". The number may be on this face or on the side of the cone depending on when the cones were manufactured.

When using the Junior cones in the Kiln-Sitter, it is important to keep in mind how the device works. The combined effect of time and temperature causes the cone to melt. The weight of the actuating (sensing) rod on the cone or bar determines when it will bend. However, the tapered shape of the Small Cone permits adjustment of the cone placement in the Kiln-Sitter, which allows the user to vary the bending time and affect kiln shut off. Placing the thin part of the cone under the sensing rod will result in a cooler firing. Placing the thicker part of the cone under the rod will result in a hotter firing.

A kiln that is loaded dense in some areas and light is others may fire unevenly and, as a result, the heavily loaded areas will probably be under fired. The three cone system (see diagram) placed in various areas of the kiln will inform you of different problem areas and give better information as to how best to load and fire your kiln. The three cone system consists of 3 large cones set in a row consisting of a firing cone (desired cone), a guide cone (one cone cooler) and a guard cone (one cone hotter). When viewing the cones through a peephole, we recommend that you wear a pair of welder's glasses to protect your eyes from injury.

It should be emphasized that Orton Pyrometric Cones are not temperature measuring devices. The specific function of a cone is to measure the combined effect of temperature and time because these factors determine when a glaze or clay has received proper heat treatment. Generally, the slower the rate of heating, the lower the bending temperature of the cone, the faster the heating rate, the higher the bending temperature. Temperature equivalent charts are to be used only as a guide.

Note: Kiln sitters take Junior (small) Cones only. Senior (Large) cones and Junior cones are not designed to bend at the same temperatures. Rate of heat rise affects bend temperature.

What is a Kiln sitter?

A Kiln sitter is a device that, by using small pyrometric cones, will shut your kiln off automatically when the cone melts and the ware is properly matured.

What is a Timer?

A 20-hour Limit Timer is a safety back-up shut-off for your kiln. Should the Kiln sitter malfunction or the cones fail to bend properly, the Timer will shut the kiln off at a pre-specified time. It acts as a safety feature and has no function in the actual firing of your kiln.

Caution: Only look into the peepholes using protective glasses.

Large Std. Cones Pictured

ORTON CONES* (box of 50)

Large, Std. (1-4 boxes) each box 7.00

Large, Std. (5+ boxes) each box 6.80

Small, Jr. (1-4 boxes) each box 6.00

Small, Jr. (5+ boxes) each box 5.80

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