Cultivation of laver seaweed as food is thought to be very ancient, though the first mention was in William Camden's "Britannia" in the early 17th century. It is plucked from the rocks and given a preliminary rinse in clear water. The collected laver seaweed is repeatedly washed to remove sand and boiled for hours until it becomes a stiff, green mush. In this state, the seaweed can be preserved for about a week. Typically during the 18th century, the mush was packed into a crock and sold as "potted laver".