Laguna B-mix Mid-fire, cone 4-6, with and without grog, fires almost white 25 lbs Your clay purchase includes some of the cost of glazing and firing that clay. Membership dues include finishing the ware produced from up to two bags of clay per month. Due to the rising cost of electricity and kiln maintenance, an additional $5 firing surcharge applies for additional bags of clay purchased at the Bay School and for any bag of clay purchased elsewhere and fired at the Bay School.