Hot Clay Advice: Orton Cones

Why use them?

Although the controllers used with modern kilns provide the temperature inside the kiln often with
time or rate function, it does not tell you the ‘heat-work’, which is a time and temperature
calculation. You will need this to know if your wares or glazes have undergone the right firing. Cones
are the only way to do this. It might not be necessary to use them all the time, but if you are getting
to know your kiln for the first time, you suspect a malfunction, or you are simply doing something
new then cones will help you.

Chart

When using cones, you will need to refer to the relevant chart. which can also be found in the product attachments.
You will notice the cones are identified with numbers, from 022-14. Note the '0' is important, for
instance cone 06 on one range is 1013°C, while cone 6 is 1243°C.

How to use them?

There are different average rates in climb of temperature, Orton uses 15°C, 60°C and 150°C. These are a
guide and not a rule. As Orton themselves say, you think of them as slow, medium and fast. Orton do
give an idea of the average climb rate, i.e. 150°C an hour. A typical firing program of 0°C-600°C 
would be at a climb of 100°C per hour, then 600°C–1240°C at 200°C per hour. From
this you could judge your firing at 150°C as an average climb and therefore in the area of cone 6.
You will notice the slower the climb the lower the temperature, but you will still be attaining the
same heat work thus the same cone value.

Traditionally, cones are used in groups of 3: A cone of a lower value, say cone 5, your target
temperature, cone 6 and higher value cone 7. When the correct temperature has been correctly met
the low will have melted completely, the target temperature will be perfectly bent and the one
higher will have bent very little.

We sell self-supporting cones which afford greater accuracy and stability. You can place them in a
row, and they do not need to be close to the elements. In large kilns you might want to put more
than one set in several places.

Orton Ceramics have useful videos explaining how the cones can be interpreted, with other common
questions explained. See link.

If you have any further questions, please call 01934 863040 and ask for the Hot Clay Technician.