What was Bow porcelain made from and why is bone ash mentioned so often?

Many Bow pieces are made to the requirements of soft-paste “phosphate” recipes that use bone ash. This ingredient changes the composition of the body, giving it the creamy hue and feel that many collectors recognize, and the glaze can be a lighter ivory colour. Researchers link the practice of making Bow figurines from bone ash to later English moves toward bone china in the early 18th century, but Bow figurines remain a distinctive soft-paste form.