We offer all four of the different types of Orton cones (Small cones, Bar cones, Large cones and Self-supporting cones).These are also known as witness cones and pyrometric cones.
The Large and Self-supporting cones are used to measure temperature
uniformity and/or if there was sufficient heatwork done to mature the
ware. Cones indicate whether the ware received an adequate amount of
heatwork to properly mature the clay or glaze. A properly fired cone
will bend over with the tip of the cone almost touching the shelf.
After firing a kiln, a simple glance at the cone can tell if the firing
The small and bar cones are mainly used in the kiln shut-off device
called the Kilnsitter. This is a mechanical device that shuts off the
kiln when the temperature inside is sufficient to cause the cone to
deform under the weight of the Kiln Sitter rod.
Temperature Equivalents use the same numbering system as small cones.
Under most conditions, the small cone or bar used in the kiln
shut-off device will need to be one number higher than the shelf cone or
witness cone. For example, to achieve a cone 04 witness cone in the
kiln a small 03 cone is generally used in the Kiln Sitter shut off device.
The only true measurement of heat-work is from a Large or Self-supporting cone placed on the shelf next to the ware. CONE
NUMBERS - Orton makes cones from cone 022 up to cone 42. Cone 022 is
the lowest melting cone and requires the least amount of heat to deform
or bend. During firing, a cone softens and melts as it is heated. Cones
used on the kiln shelf bend due to the effects of gravity pulling the
tip down. This bending indicates the cone and the ware have received a
specific amount of heat. It typically takes 15 to 22 minutes for cones
to bend fully once they start bending. Each higher cone number requires
more heat to bend. A cone 01 needs less heat treatment than cone 1 and
cone 020 needs less than 019. It is important not to confuse the
lower maturing cones and bars, whose numbers begin with an 0, with the
higher cones and bars not containing this prefix.
Although cones do not actually measure temperature, cone bending
behavior and temperature are related. Generally, the faster the firing,
the higher the temperature required to bend the cone and the slower the
firing, the lower the temperature required to bend the cone. The 6
oclock position (90 angular degrees) is considered the end point of
Typical uses for cone numbers are as follows:
NUMBER: 022 TO 011 - Used in firing of overglaze decorations,
lusters, enamels and decals and for glass fusing, slumping and
decorating. The temperature
equivalent range is approximately 1050 - 1550F (560 to 850C).
NUMBER: 010 TO 3 - Made as a regular series (red,
iron-containing cones) and as an Iron Free series for use in reducing
atmospheres. These cones are used in the firing of craft and art
bodies, for wall tile, glazes and some structural clay products. The
temperature equivalent range is approximately 1600-2150F (890 to
NUMBER: 4 TO 12 - Used in firing porcelain, floor tile, china,
stoneware, structural clay products and some refractory materials. The
temperature equivalent range is approximately 2175-2345F (1180 to
NUMBER: 13 TO 42 - Used for firing industrial products up to 3659F (2015C).
and Bars have 11 different colors.
Knowing the colors can make it easier to tell at a glance which cone you
have. Cones have their number stamped on the side and that is the most
important thing to look at since there are colors shared by different
There are 10 different colors that span Large and Self Supporting as
well as Small Cones and Bars. Cones and Bars from 05 to 3 are dark red
because of the iron that they contain.
Here is a guide to Orton cones colors.
Orton Pyrometric Cones and Bars
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