Flax was used as early as prehistoric times to make linen. Representations of the cultivation and processing of flax appear in numerous tombs. The flax harvest could take place at different times, depending on what the flax was to be used for. Young, green plants produced a fine thread, mature plants strong fibres for rope, for example; in the phase just before the flax ripened, when the plants were yellow, the fibres were suitable for making linen. The age of the plants used affected the colour of the final product, too, something that was also determined by the way the flax was processed. Some pieces of linen were bleached to achieve a white colour. Different qualities of linen were recognized: lists from the Old Kingdom, for example, mention various types. Royal linen was the highest quality.