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Discharge Agents for Removing Dye

Discharging is the chemical removal of dyes. You may use discharge dyeing simply to remove all of the dye from a piece of fabric (insofar as possible), or you may use it as an additional design technique. Discharge agents are required for "reverse tie-dye", in which a light design is produced on a dark background. They are also ideal for stamping designs onto dyed fabric.

Not all dyes are capable of discharge. Many dyes are completely resistant to the effects of all discharge agents. It is impossible to predict whether this is the case without actually testing with some bleach. Even if you depend for years on a certain source for dark clothing or fabric for discharging, your supplier may suddenly switch to a different dye of the same color, without warning. Always test every single bolt of fabric, and every single dye run of clothing, to be sure whether or not it is dischargable. Many fibers should never be discharged. Never attempt to discharge polyester or spandex. Use only gentle reductive discharge agents on wool, silk or nylon. Chlorine (hypochlorite) bleach will permanently damage synthetic fibers and all protein-based fibers such as wool and silk. There is no way to remove the yellowing from bleached polyester. However, rayon can be bleached, with great care.

If you dye your own fabric for discharge, dye selection is critical. Among the deservedly popular Procion MX type fiber reactive dyes, only the yellows are very dischargable; red MX-5B and blue MX-2G also discharge reasonably well. A better choice for discharge is the Vinyl Sulfone class of fiber reactive dyes.

Even among dischargable dyes, the results can vary from nearly white to dark brown. One of the attractions of discharge dyeing for dye artists is the oftentimes ghostly range of colors obtained from the damage to the existing dye.

There are two classes of chemicals used for discharging dyes: oxidative and reductive discharge agents, both described below....

Different chemicals for oxidative discharge dyeing

Sodium chlorite, NaClO₂, is used in the textile industry but not at home or in the studio.

Sodium hypochlorite, NaOCl, is ordinary household bleach, typically found in strengths of 5.25% or 6%. It is commonly known as "chlorine bleach", though it is more correct to refer to it as hypochlorite bleach. NaOH may also be listed on the label; it increases the pH of the bleach. Hypochlorite bleach must be neutralized after use with a product such as Anti-Chlor (sodium bisulfite or sodium metabisulfite), Bleach Stop (sodium thiosulfate), or 3% hydrogen peroxide (H₂O₂), as otherwise the fabric continues to be degraded in spite of washing. Anti-Chlor is by far the most economical of these products.

The big warnings about hypochlorite bleach are:

       - never mix it with ammonia-containing cleansers, and
       - never mix it with any acid

Mixing hypochlorite bleach (NaOCl) with ammonia (NH₃) produces deadly and/or explosive chemicals such as chlorine gas (Cl₂), nitrogen trichloride (NCl₃), and hydrazine (N₂H₄). Mixing hypochlorite bleach with an acid, such as vinegar, also produces deadly chlorine gas.

Avoid all skin exposure to bleach. Wear safety glasses, non-disposable rubber or nitrile gloves, and old clothing when working with hypochlorite bleach, and never work with it in an unventilated space. It is best to use hypochlorite bleach out-of-doors or in a fume hood. A dust mask provides no protection; wear a cartridge respirator to protect your lungs. (See PRO Chemical & Dye's safety equipment.)

Calcium hypochlorite is very similar in use to sodium hypochlorite.

Hydrogen peroxide is an oxidative bleach, but it is much kinder and gentler to the fiber than hypochlorite bleach. While hypochlorite must never be used on protein fibers such as silk and wool, peroxide is very commonly used as a bleach for wool as part of the usual processing before dyeing. Most dyes are relatively unaffected by peroxide, as compared to hypochlorite or to reductive discharge agents. Hydrogen peroxide is safe and effective for neutralizing hypochlorite bleach, though it is much more expensive per use than Anti-Chlor. Related to hydrogen peroxide are sodium perborate (NaBO₃), found in laundry detergents as a colorsafe bleach. and sodium percarbonate, the main ingredient in "oxygen based," "colorsafe" laundry bleaches, such as OxyBoost® or OxyClean®. Perborate is produced by reacting hydrogen peroxide with sodium borate, while percarbonate is produced by reacting hydrogen peroxide with soda ash; both turn back into hydrogen peroxide upon being dissolved in water.

Different chemicals for reductive discharge dyeing

Sulfur dioxide, SO₂ is the chemical that does the reducing, no matter which of the following chemicals you use to reduce your dye. Originally it was produced by burning yellow sulfur in the presence of the fiber to be bleached. This is probably not a good approach, for your own health; better to use one of the other reducing discharge agents to produce it on the fabric.

Thiourea dioxide, also known as aminoiminomethanesulfinic acid or formamidine sulfinic acid, is sold under the brand names Thiox, Spectralite, and Dharma Dyehouse Color Remover. The chemical formula is H₂NC(=NH)SO₂H. It is used in indigo dyeing and other vat dyeing as well as for discharge. It costs more than sodium hydrosulfite, but you use less.

Sodium hydrosulfite, also known as sodium dithionite, sodium sulfoxylate, and sodium sulphoxylate, is the active ingredient in Rit Color Remover, Tintex Color Remover, Dylon Run away for Whites, and Carbona Run Remover, all of which also contain sodium carbonate (soda ash). (I don't know whather Jacquard Color Remover contains the same ingredients, but I suspect it does.) Its chemical formula is Na₂O₄S₂. This is the chemical used by Carter Smith in Kate Broughton's book Textile Dyeing: The Step-By-Step Guide and Showcase. Storage of large quantities is unsafe due to its flammability.

Sodium formaldehyde sulfoxylate, also known as sodium hydroxymethanesulphonate, sodium hydroxymethanesulfonate, and formaldehyde sodium sulphoxylate, is the chemical used in Formosul and Rongalite. Its chemical formula is CH₃NaO₃S. It can be used under acid as well as basic conditions.

Although sodium sulfite (Na₂SO₃) and sodium bisulfite (NaHSO₃) are listed in some documents as reductive bleaches, I cannot find a recipe for either's use for this purpose, though it's easy to find recipes for the use of the other reducing agents above. At our level it seems that these are only used to neutralize hypochlorite bleach. Do NOT confuse them with sodium bisulfATE (Na₂SO₄), which is used to destroy cellulose; remember the mnemonic, "bisulfATE ATE my fabric."

A project for stamping designs on cotton fabric with bleach

Not all dyes can be discharged; some will retain their original color no matter what you do. Before attempting this project, test the garment you wish to bleach, to make sure that it is able to lose color, by applying a small amount to a hidden part of the fabric, on a seam; beware of accidental drips. Also, do not use chlorine (hypochlorite) bleach on any garment that contains synthetic fibers such as polyester or spandex, or animal fibers such as silk or wool. On silk or wool, you can use a sulfur-based discharge agent such as Jacquard Discharge Paste, Formusol, Thiox, or Rit Color Remover; these will not work on polyester or spandex, however.

The easiest way to use chlorine bleach for this project, on 100% cotton garments only, is to buy a product called the Clorox Bleach Pen. These pens contain hypochlorite bleach that has been thickened, so it will not run and spread as easily as unthickened bleach will. For larger projects for which one bleach pen would be too small (and a large number of bleach pens would be too expensive), you can buy a special bleach thickener to prepare thickened bleach yourself; PRO Chemical & Dye sells a product for this purpose under the name Monagum, while Dharma Trading Company sells something called Bleach Thickner. (See my list of Sources for Dyeing Supplies Around the World for links to these and other dye retailers.)

Before you begin your project, you must prepare a stop-bleach bath. Chlorine (hypochlorite) bleach must be neutralized immediately after use or it will continue to eat away at your fabric, eventually creating holes. As soon as your fabric has discharged to the desired degree, rinse it in water and then plunge it into a bath of Anti-Chlor, Bleach Stop, or another bleach neutralizer, available from your dye supplier. Do not use vinegar, as it will create caustic and dangerous chlorine compounds when it reacts with bleach. If you have no other bleach stopping chemical, you can soak the garment with 3% hydrogen peroxide, such as is sold in drug stores as an antiseptic; this costs more than Anti-Chlor, but is safe and effective. Anti-Chlor is by far the most economical bleach stopping agent. Get this ready before you begin to apply the bleach. You can use Anti-Chlor or Bleach-Stop in the washing machine, or in a plastic basin or a bathtub.

When stamping fabric, you must select (or make) a stamp without small details, as these will work only on paper, not on fabric. Using the bleach pen, squeeze a small amount of thickened bleach gel onto the stamp and spread it with the brush applicator end until it is smooth, then apply to the fabric. Apply more bleach to the stamp before making the next mark. Alternatively, you can make a stamp pad by placing white paper towels in a plastic meat tray or a glass plate, and soaking them with chlorine bleach. Be careful to do the latter only outside or in an extremely well ventilated place, and wear clothing that you don't mind ruining. Remember that chlorine bleach is quite toxic; wear rubber gloves to limit skin exposure. Also wear safety glasses, when working with liquid bleach.

After all of your stamped designs have visibly lightened the garment - watch closely, as it might take only a few seconds, or up to half an hour, depending on the specific dye that was used in the garment - rinse the garment and stop the bleach action with your choice of bleach stop chemical, then launder the garment as usual.

Information about other ways to dye

For information about other types of dye, see About Dyes.

         

All of the pages on this site are copyright ©1998-2024 Paula E. Burch, Ph.D.

Portions of the text on this page were originally published, by me, in my All About Hand Dyeing Q&A Blog, on July 8, 2006 and in the Dye Forum on this site on May 17, 2006 and May 1, 2006.

Page created: July 18, 2006
Last updated: July 18, 2006
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