Mercerized cotton is cotton which has been treated with sodium hydroxide to bring out certain properties first discovered by John Mercer in 1851. In 1890, Horace Lowe added an additional step to the process, and the British cotton industry began to take an interest in this type of cotton, which is available today in a wide range of incarnations from thread to completed garments. When treated properly, mercerized cotton is stronger, smoother, and shinier than regular cotton. In addition, it takes dye more readily so that manufacturers can create rich color saturation in their cottons. The brilliant, lustrous hues of this cotton can be found in fabric stores, yarn shops, and department stores all over the world.
John Mercer discovered that immersing fibers such as cotton and linen in a caustic soda bath would increase their strength and also allow them to take dye more readily. He patented his fiber work, but the cotton industry did not express very much interest in it. It was Horace Lowe who popularized the process, by discovering that keeping the fibers under tension while they were soaked yielded a more lustrous thread. Mercer's name is presumably given to the process to recognize his important initial discovery, which paved the way to Lowe's refinement of the treatment.
Mercerization starts with gathering the cotton and spinning it normally. Because cottons with long fibers take better to mercerization, Pima, Egyptian, and Sea Island cotton are usually chosen for the process. The cotton thread is held under tension and submerged in a highly alkaline bath of sodium hydroxide in a percentage which ranges, but usually hovers around 22%. After treatment, the mercerized cotton is placed into an acidic bath to neutralize it. Once this process is complete, the cotton can be dyed and knitted, woven, or packed as stand-alone spools of thread.
The terms "pearl cotton" and "pearle cotton" are also used to refer to Mercerized cotton, because of the deeply lustrous appearance of the finished cotton thread. In addition to having rich color saturation and a shimmering appearance, this fabric is also much stronger than conventional cotton thread. The process shrinks the cotton fibers, tightening and smoothing the grain of the thread. Because the cotton is preshrunk, mercerized cotton also tends not to shrink as much as regular cotton, so consumers can be more confident about the fit of mercerized garments.