King Arthur Baking Company Glass Sourdough Crock with red 0.25-inch markings helps to easily monitor if starter has reached its highest point ready for use or if it is time for a feeding. Stainless steel lid fits loosely to allow gasses to escape; non-reactive borosilicate glass is ideal for sourdough starter. Holds enough starter for several loaves of bread; Made from borosilicate glass and stainless steel, King Arthur Baking Company Glass Sourdough Crock is free from lead, cadmium, BPA, and PFAS, and hand washable.