Refers to the container filled with DYE solution in which fabrics are immersed to take up the colour.
Typically the dye bath is kitted out with two rollers on either end that carefully control the rate, time and tension at which the fabric is pulled through the dye bath. Fabric dyed in the piece is wound onto a roller at one end and immersed into the dye as it is released, then re-wound onto the second roller at the other end.
Finished items are finally washed by hand, as one would domestically.