Cotton fiber grows attached to cotton plant seeds. Cotton and cotton blends dominate the market. Clothes of cotton, wool and animal skin were worn. They are normally made from natural fabrics such as cotton or silk. Tangkas are painted on cotton or silk. Toddlers wore washable dresses called frocks of linen or cotton. It is far cheaper to produce than wool, cotton, or silk. Wool ignites at a higher temperature than cotton and some synthetic fibers. The trade was mainly in timber, silk, cotton and opium. Egypt became a major producer of linen and cotton cloth. The textile industry wove cotton produced in the South. Nubia became a center of iron-making and cotton cloth manufacturing. Textiles were created from plant fibers including cotton and agave. Activities included coal mining, textile production, particularly cotton, and fishing. Other important crops are maize, tobacco, mango, cotton and sugar cane.