clay and cones??

What are CONES? As in, what the heck does it mean when a commercial bottle of glaze says “fire to CONE 6” ?? Why not just say fire to xyz temp??
CONES refer to PYROMETRIC CONES… An ancient “technology”

Archaeologists working at Northern Song period (960 to 1127 AD) kiln sites in the Chinese provinces of Shaanxi and Shanxi have reported that pyrometric cones about five centimetres tall and made from loess were used to help control the firing of the kilns.

Read about pyrometric cones at WIKIPEDIA, where the above quote comes from.

The link below opens to a chart specifically designed to correspond with ORTON BRAND pyrometric cones. Looking at the chart may illustrate things as well….