Test Your Kiln's Uniformity With Witness Cones

Using Witness Cones

Using witness cones properly gives good insight into your kiln's exact firing temperatures. Often, using three cones is the best way to measure heat work:

• Guide Cone – one cone number cooler than the firing cone
• Firing Cone – cone number the kiln is being fired to
• Guard Cone – one cone number hotter than the firing cone

Place the trio of cones in different areas of the kiln, far enough away from ware so they will not bend into it. At the end of the firing:

• The Guide Cone should show an over-fire
• The Firing Cone should show an accurate/even fire
• The Guard Cone should show no bend or under-fire

Once you’ve determined your kiln’s performance in different areas, you can use cone or thermocouple offsets to help adjust your kiln's temperatures.

When to Use Witness Cones

Witness cones do not need to be fired with every firing, but it is good to use them occasionally to ensure the kiln is continuing to fire properly.

If you have questions about using cones or adjusting your kiln for heat work, give us a call — we’re happy to help!