Until the mid-19th century its main industry was kelp collection and export primarily operated by Staffa MacDonald who bought the island in 1785 because of the kelp. At the turn of the 19th century, the kelp industry supported a large amount of the population. It was seasonal work, with collection taking place in the months of May, June and July, when it was considered possible to dry it outdoors. The dried kelp would usually then be burnt, and the ash used to produce various products, including fertiliser (mostly soda ash) and iodine as well as glass and soap. The ruined kiln on the south shore may have been used for this. Between 1817 and 1828, no less than 256 tonnes of kelp were collected in Ulva. Kelpers collected on average, a wage of two shillings a week, and a stone of wheat.