The history of yarn dyeing machines is traced from the 19th century to the present. The mechanization of hank dyeing began with a competition between two types of machines: those in which the yarn hanks were circulated in a static liquor and those in which the liquor was circulated around yarn hanks held in a fixed frame. Designs were modified to improve such characteristics as dye penetration or shade uniformity. The first patent was granted for a package dyeing machine in 1858. Many of the earlier designs were used for dyeing cops, which are packages of yarn produced during mule spinning.