Merchants imported olive oil in glazed earthenware jars. The jars were glazed as oil seeps through unglazed pottery. These date from about 1501-1700. Most of the oil was used in the soap industry: olive oil made delicate 'castile' soap. The alternative was harsher soap made using animal fats such as lard or tallow. For centuries in the British isles olive oil was used in industry and medicine, not in cooking. Until about the 1970s, adventurous cooks had to buy their olive oil in tiny bottles from the chemist.