Prewash: All fabrics must be pre-washed before dyeing. Fabrics may have invisible stains that will affect the evenness of dyeing, or they may have finishes that will have the same effect.

Use special detergent: For the very best and brightest results, it is best to use a special detergent for this purpose, because many commercial laundry detergents container optical brighteners which occupy the same positions you want the fabric to make available for the dye, and brighteners make deep colors look less intense. Appropriate detergents include Synthrapol, or pure SDS (sodium dodecyl sulfate or sodium lauryl sulfate), commonly sold in feed stores under the brand name Orvus. However, results of dyeing are generally acceptable even when ordinary detergents have been used for pre-washing. If you don't have Synthrapol, don't worry; just use whatever detergent you have.

Beware of starch: Sometimes fabrics will have been treated with starch before sale. Starch presents a major problem for the dyer. It will take up dye readily itself, then gradually wash out, giving the mistaken appearance of dye bleeding. Starched fabric is not suitable for dyeing, because washing does not remove most of it. To determine whether your fabric contains starch, drop 2% tincture of iodine on it. Iodine turns an intense blue in the presence of starch.

Permanent press and other resins. If the fabric has been treated with a no-iron finish, or with a stain resistant coating, or with any sort of water repellant, dye will not be able to reach the fabric evenly, resulting in pale, uneven dyeing. A permanent press finish can be removed with muriatic acid, but the chemical is too hazardous to be suitable for home or studio use. Also, some after-dyeing dye fixatives, which are invaluable for combatting the poor wash-fastness of direct dyes and all-purpose dyes, will afterwards prevent dye from reaching the fiber properly. This may present a problem in dyeing the many garments that have been commercially dyed with direct dye.

Other potential problems. Occasionally, different parts of a garment will be made from more than one lot of fabric, which look the same before dyeing, but then look quite different after dyeing. There is nothing to be done about this except chalk it up to acceptable losses, or dye only blank garments that have been sold as "PFD" (Prepared For Dyeing").