Name: Neal
Message: I need some advice.  I vat-dyed a white, 100% viscose-rayon dress using a what I thought was an incredibly weak solution of Procion MX #12 (Light Red)---I intended to get a pastel but instead it came out a chemical, bubble-gum pink.    Bleach, I know, isn't good on rayon.  Is there anything I can use that will lighten the color evenly?  (this was an expensive dress).   Or am I better off dying the dress a darker color or living with it as is?

How weak was your dye solution? The last time I tried to get a pastel, I too obtained a color that was much brighter and more intense than I wanted. I think the right amount of dye to use to get a pale color is only one-tenth as much as usual, but I was using, I think, one-quarter as much dye as usual. PRO Chemical & Dye suggests using only 1 teaspoon, or 2.5 grams, of dye to produce a pale shade on one pound (454 grams) of cotton, but you must remember that both viscose rayon and mercerized cotton will produce markedly more intense colors than unmercerized cotton, because the cellulose in the more highly processed fiber is more accessible to the dye. Perhaps 1/4 to 1/2 teaspoon (or 0.6 to 1.3 grams) of red dye would be more appropriate for dyeing a pound of rayon to a pastel pink.

When this happened to me, I was dyeing a cotton PFD dress rather than rayon, and, when I tried to remove it, I used sodium hydrosulfite, which I purchased as Rit brand Color Remover. This product is sold in many places, right next to the little boxes of Rit brand all-purpose dye. You may also find it sold under the names Carbona Color Run Remover or Dylon Colour Stripper, depending on your location. A washing machine load requires anywhere from one to four boxes of Color Remover, depending on the size of the washing machine and the amount of color removal that is desired. The color I ended up with was much lighter than my original overly intense color, but it was an interesting brownish shade. You will often obtain interesting ghostly colors as the result of removing dye, colors which are different from the original dye color, not just lighter.

Your red dye, red MX-5B, should discharge better than the similarly-colored red MX-8B, which is commonly called fuchsia. It is expected to produce some sort of beige color, rather than the only somewhat lighter magenta produced by discharging fuchsia. Here is a link to an adaptation of Dharma's lists showing what colors are obtained by discharging from various MX dyes. 

Actually, hypochlorite (chlorine) bleach is not such a terrible thing for rayon. Rayon is tremendously fragile when wet, but it is being wet that makes rayon weak, rather than the bleach itself. This is in contrast to synthetics such as polyester and nylon, and animal fibers such as silk and wool, which are badly damaged chemically by exposure to bleach. A heavy rayon garment might tear upon being lifted from water, but careful treatment is usually sufficient to prevent damage. Placing it in a large mesh lingerie bag may be helpful. 

Whenever you use chlorine bleach, you must follow its use, after rinsing with water, by neutralizing the bleach chemically, using Anti-Chlor (the most economical answer, purchased by mail order from your dye supplier), or Bleach-Stop, hydrogen peroxide, or strong color-safe chlorine-free "oxygen" bleach, such as OxyBoost. You must not use an acid, such as vinegar, to neutralize chlorine bleach, because the reaction produces even more toxic and caustic compounds. The hydrogen peroxide that is sold as an antiseptic is fine for this purpose, but it is much more expensive pr use than Anti-Chlor. Properly neutralizing bleach on fabric will stop it from degrading the fabric further, and will prolong the life of the garment. There is no need to neutralize the sodium hydrosulfite found in Color Remover; it is gentler to the fabric than hypochlorite bleach, and will be removed simply by washing.

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