The DFC Cupels are manufactured from bone ash, a composite material and
Magnesite (MgO). Since they are used in assaying to absorb the lead in a
assay button from the fire assay process, the quality of the raw
ingredients will mean good lead absorption, and a more durable cupel
when being handled prior to cupellation. DFC offers one of the highest
quality cupels available.

Bone ash is Ca5(OH)(PO4)3, it is derived from dried animal bones, and has excellent lead absorption.

Magnesite cupels are more durable at room temperatures, and survive shipping and handling better than bone ash and composite cupels.

Composite cupels are a mixture of bone ash and Portland cement. They are more durable at room temperatures, and survives shipping and handling better than bone ash cupels.