Ann McElroy asked on Facebook,
I had thought turquoise acid dye had chrome in it. Someone told me they don’t use chrome anymore. I couldn’t see anything on your site. Do they still use chrome?
Chrome is certainly still used in many dyes. It’s invaluable for making long-lasting dyes for wool, dyes that are resistant to washing and fading. Chrome that is contained in the molecular structure of a dye, as in the metal complex or premetallized acid dyes, is far safer for us to use, and for the environment when we dispose of any excess, than the use of chrome as a mordant. I strongly recommend against using chrome as a mordant, but it is not difficult to safely use chrome-containing acid dyes.
Chrome mordants are far more dangerous than chrome-containing acid dyes for two reasons: they contain the carcinogenic hexavalent form of chromium, instead of the safer trivalent form found in the metal complex dyes, and the quantity of chromium present is vastly greater in the chrome mordant solution than in the metal complex dyes.
Which turquoise acid dye you are talking about is another story. There are so many different types of acid dyes! The only way to answer this question is to look at each of the commonly used turquoise acid dyes separately. (It is a good idea to look at the MSDS from your dye seller for each individual color of each dye that you use.)
acid leveling dyes
The old Kiton acid leveling dyes included a turquoise-colored acid dye called Erioglaucine, whose generic name is Colour Index Acid Blue 9. This dye never contained chromium. ProChem no longer sells the Kiton dyes, but the dyes are still used in such lines of acid dyes as Cushing and Landscape Dyes, though no specific information as to which dye types are included in which colors. Interestingly, Acid Blue 9 is the exact same dye that is known as FD&C Blue #1 or E133, which is popularly used in artificially colored candies, drink mixes, and the blue alcoholic liqueur curaçao. This is the dye you’re using when you dye wool with unsweetened blue Kool-aid.
Alphazurine A, or Acid Blue 7, is a popular blue acid dye which ProChem sells as their Washfast Acid Blue 478, Jacquard Products sells as their Jacquard Acid 624 Turquoise, and Dharma Trading Company sells as their Dharma Acid 407 Caribbean Blue. Like erioglaucine, alphazurine A is an acid leveling dye, which means that it is not particularly washfast, but it is easy to use to produce smooth level solid colors. This dye, too, never contained chromium.
Among the Lanaset line of acid and reactive dyes for wool, ProChem sells Sabraset Turquoise 480, and Maiwa sells the same dye, as Lanaset Turquoise 5G. While some of the dyes in the Lanaset dyes do contain chromium, the turquoise does not. This dye does not have a Colour Index generic name, but we know its full chemical name, which indicates no heavy metal component. The MSDS also indicates no heavy metal content.
There are many turquoise dyes that are based on the beautiful copper phthalocyanine ring, which has a large flat molecule structure similar to that the the hemoglobin ring in blood or the chlorophyll ring in green plants. (Each of these rings has a metal ion in the center; where phthalocyanine has a copper atom in the middle, hemoglobin is centered on iron, while chlorophyll is centered on magnesium, and the pink molecule of vitamin B12 is centered on an atom of cobalt.) There is no substitute for copper phthalocyanine if you want a particularly bright clear turquoise; all of the best bright clear turquoise dyes, of whatever class, are based on this structure. None of these phthalocyanine dyes contain chromium, as they use copper, instead.
Among the very bright clear turquoise dyes based on copper phthalocyanine are the fiber reactive dyes, Procion MX turquoise and Remazol turquoise. Although these fiber reactive dyes are usually used on cellulose fibers such as cotton, along with a high-pH substance such as soda ash, if they are used on protein fibers such as silk or wool, in the presence of an acid such as vinegar, and heat-set with steam or in a simmering dyebath, they actually function as acid dyes, thanks to the sulfonate groups which are also what make the dyes soluble in water. An acid dye based on the same copper phthalocyanine ring is Acid Blue 249, but I don’t know of a source for this dye for hand dyers. The brightest turquoise acid dye is Dharma Acid Dye #424 True Turquoise; this dye is classified in the Colour Index as a direct dye, Direct Blue 86, for historical reasons (it was described as a direct dye first), though the only difference between it and Acid Blue 249 is that it has only two sulfonate groups, whereas Acid Blue 249 contains four of them. Like the reactive Procion turquoise, it works well when used on wool or silk in an acid dyeing recipe, along with an acid and moist heat. Below are pictures of the structures of Acid Blue 249 and Direct Blue 86:
The amount of copper in the copper phthalocyanine dyes is only between 1% and 5% of the dye, by weight, not enough that we have to worry about toxicity or environmental damage being caused by it.
metal complex dyes
As a general rule, only those dyes which are classed as premetallized, or metal complex, contain chromium. (The phrase ‘metal complex’ refers to the exact same dye class as the word ‘premetallized’.) These dyes tend to be exceptionally washfast and lightfast, but usually duller in color than the leveling acid dyes. An excellent example is the black dye contained in Lanaset Jet Black (in combination with another dye), as well as ProChem’s Washfast Acid Black 672 and H.Dupont’s Noir Concentre. These metal complex dyes are so wash-resistant that they are washfast even in hot water, at 140°F, rather than only in cool water like other types of acid dyes. The “Cr” in the center of the chemical structure, below, for Acid Black 172 stands for the chromium atom that helps to make this such a permanent dark black dye.
As far as the safety of the hand dyer is concerned, I feel that there is no need to worry much about whether or not a particular dye contains chromium. You should be cautious never to eat or breathe any textile dye, and always wear gloves when working with it (though obviously you can be more relaxed with Acid Blue 9, since it has passed safety testing for use as a food dye). It is always especially important to avoid inhaling dye. The quantity of chromium in good-quality dyes is low enough that ordinary caution is adequate, when working with small quantities. For example, I calculated, in the October 6, 2006 entry in my blog, that one teaspoon of Lanaset Black B dye powder contains 0.08 grams of chromium, which after being diluted with fifty gallons of water, as when discarded down the drain with household waste water, will meet the US EPA standard for chromium content of drinking water in the US, which is 100 micrograms per liter. This is in the trivalent form of chromium, which is far less hazardous than the hexavalent form of chromium.
In contrast, I recommend strongly against using chrome as a mordant in hand dyeing. The chromium in potassium dichromate is in the carcinogenic hexavalent form. One recipe (in Liles’s Art and Craft of Natural Dyeing, 1990) calls for 10 grams of potassium dichromate per pound of wool, in a five gallon dyebath. This is a very large amount of chromium, compared to the amount of chromium in a metal complex dye, and it is in a far more dangerous form. This quantity, if swallowed, is enough to kill several people; lower doses, whether swallowed, inhaled, or absorbed through the skin, can cause severe burns, blindness, birth defects, kidney damage, cancer, and other harm. (See PubChem.) The chromium that becomes a part of the dye-fiber complex is transformed to the trivalent form, but the risks of working with potassium dichromate in the home are too great.
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