There are many weaving families in Teotitlán del Valle and Santa Ana del Valle, estimated by some to total 150. However, they vary greatly in quality and style. The finest work is carried out by the far smaller number of families who create dyes from natural substances and use pure hand-spun wool. Nearly all of them work on vertical shuttle looms operated with foot pedals and treadles, dating back to the 16th century, when they were introduced by the Spaniards. This is in contrast to the vast majority of families using chemical dyes and acrylic fibers introduced in the 1920s. These can be produced and processed far more rapidly and are less costly.