The Antiga Collection is 100% natural earthenware made from barro negro (black clay). The unique black clay can maintain the temperature of food or liquids, either hot or cold, for a long period. Terracotta (clay) is traditionally a reddish/brown earthenware that is kiln fired. The distinct black colour of this collection is a result of the kiln cooking process that removes oxygen, alongside the type of porous clay used. In order to make this clay piece oven safe it must be fully submerged in water for a full 24 hours. This procedure only needs to be done one time before its first use. These clay pieces are sensitive to extreme changes of temperatures. Food safe. Hand wash only. Made in Portugal.