We make marking crayons in two types, wax based and ceramic based.
The wax based crayons work well on coarse bodies like abrasives, an d the pigment is black iron oxide which persists after firing to high temperatures. Other colours can also be made.
The ceramic crayons can be made in various colours from frits, and are wax free, suitable for underglaze.
The most popular crayon is cobalt oxalate based. It writes pale pink, almost invisible on green ware. After tempering at 400 degrees, it shows up black, and after firing it comes out cobalt blue.
It can therefore be used to track the identity of an item and also its firing status.
Dev no: 21800