Message: Hello,
I have tried a dye mentioned in one of your articles called "Rhodamine B". I used less than 0.25% dye on the weight of a nylon/spandex fabric. I notice it bleeds VERY BADLY in washing. (I only used a very small amount and got a bright pink shade). How do I stop it from bleeding? I also have noticed this same codition on nylon/spandex dance leotards of the same colors. I tried a acid dye "fixative(brown goo)" at pH 5.5 and it still bleeds. Any ideas how to correct this?

What kind of recipe did you use in applying the Rhodamine B dye? Did you heat the fabric in the dyebath to simmering for half an hour or longer, along with Synthrapol and an acid such as citric acid, ammonium sulfate, or vinegar? I have no idea what your "acid dye fixative(brown goo)" might be. Did you use it in the dyebath while heating, or as an after-fix? 

Rhodamine B has two generic names, Colour Index Acid Red 52 and Colour Index Basic Violet 10. It is sold by many dye suppliers, including Jacquard Products which sells it as their 620 Hot Fuchsia acid dye, and PRO Chemical & Dye which sells it as their WashFast Acid dye 370 Rhodamine Red. (See "Which Washfast Acid colors are pure, and not mixtures?".)

ProChem's instructions for using this and other dyes in their WashFast Acid Dye series are among the most reliable anywhere; see their instruction sheet "Immersion Dyeing Nylon using WashFast Acid Dyes" (PDF file). If you did not follow a similar procedure, the best solution would probably be to do so now, following the directions precisely except for not adding additional dye. This will allow the dye molecules to bond as well as possible to the fiber.

Unfortunately, high heat can be damaging to spandex fibers, in many cases causing them to weaken and lose elasticity, but acid dyes are unlikely to work well without sufficient heating. (See "How to Dye Spandex".) What temperature limit does the care labeling indicate for washing your fabric?

To remove unfixed dye, you can try soaking the fabric overnight in the hottest water permitted by the care label. Soaking will remove more excess dye than simply washing will, and the hotter the water, the better it will wash out unattached dye.

Since I do not like heating nylon/spandex blends to simmering temperatures, because I fear damage to the spandex, for these blends I prefer the use of "pigment dyeing", in which a fabric paint is substituted for the acid dye. This results in somewhat more uneven and aged looking results than a true dye, but it avoids the possibility of damaging the fiber blend with too much heat, and it can look very good, depending on the desired look. Two good possibilities are Dharma Trading Company's Dharma Pigment Dyes, which are available in fluorescent colors, or Jacquard Products' Dye-Na-Flow, a fabric paint intended to mimic dye. Dye-Na-Flow requires heat-setting unless you add some Airfix, which you can order from Jerry's Artarama (one of the few mail-order sources for AirFix). Dharma Pigment Dyes are said not to require heat-setting on untreated nylon.

For most acid dyes, a good solution would be an after-fix treatment to try to make the dye more washfast, such as Retayne (see "Commercial Dye Fixatives"). Unfortunately, Retayne might not work on Rhodamine B, because this dye is actually a basic (cationic) dye, although it is sold with acid dyes and used with the same recipes; the positive charge on the dye will prevent a cationic dye fixative from working.

I'm afraid I need to mention the drawbacks of Rhodamine B. Like most, if not all, fluorescent dyes, Rhodamine B is poorly lightfast, especially compared to other dyes in the WashFast Acid dye series. (See "Lightfastness of Different Types of Dyes".) While there are many acid dyes which are rated at 6 or 7 on a scale of 1-8, where the higher numbers indicate better resistance to fading in the light, Rhodamine B is rated at only 2 to 3, indicating that it fades rather quickly in bright light. Items dyed with Rhodamine B should be dried indoors after washing, not outdoors on a line, and they should be stored in the dark; other dyes should be substituted if lightfastness is important.  It is also rated at only a 3, on a scale of 1 to 5, for washfastness. Even more seriously, Rhodamine B is listed by some agencies as a possible carcinogen and possible mutagen; take appropriate laboratory precautions against exposure, and if you use a cooking pot to heat your dyebath, please do not reuse it for food. Here is a link for safety information about Rhodamine B.

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