Category Archives: about dyes

Pre-reduced indigo: natural versus synthetic

Name: Jen

Country or region: US

Message: I’m doing research on pre-reduced indigo crystals. I’m finding that they’re being called everything from freeze-dried to instant and claims of them being ‘natural’, extract, etc. This flies in the face of what I’ve also been told directly by an importer- if it comes from India it’s all synthetic. Even the stuff one seller is claiming produced in Japan has an import label from India! So you can see confusion.
Any information or insight you’d be nice enough to share is most appreciated.

Hi Jen,

I believe that I’ve NEVER encountered pre-reduced indigo that was not synthetic. Those who wish to use only plant-derived indigo must do more work to reduce their indigo themselves.

I suspect that there is no difference at all between pre-reduced indigos that are listed as being freeze-dried, dried, or instant, merely different ways of describing the same product. Indigo “extracts” appear always to be the normal oxidized form which must be reduced by the dyer before use. Note that pre-reduced indigo is not 100% reduced; the various retailers all specify that their pre-reduced indigo is 60% reduced. The remaining 40%, which is in the oxidized form, is unusable unless the dyer chemically reduces it in the indigo dyeing vat. (Both synthetic indigo vats and natural fermentation indigo vats produce chemical reduction.)

Often a retailer’s advertising copy reads as though their pre-reduced indigo is natural, but if they are both reputable and careful you can see that it is not. For example, Dharma Trading Company, which is good about what claims they make, says:

As an alternative, try this Pre-reduced Indigo. Synthetic Indigo (chemically identical to natural Indigo) has been pre-reduced chemically, then dried, so it dissolves in water right off the bat….This all makes it have a lower environmental impact for the dyer than taking the original natural or synthetic Indigo from start to finish with all the chemicals involved.
(source)

Jacquard Products starts off saying “This natural vat dye exists in plants all over the world”, but concludes clearly with “Jacquard’s indigo is a synthetic organic and comes pre-reduced 60% for unprecedented ease of use.” (source)

“Organic” is a difficult word for the dyer, because an organic chemical is any chemical that contains carbon; it has nothing to do with organic farming. All dyes, whether natural or synthetic, are organic chemicals, aside from a few mineral colors that are not really of interest. However, many dyers mistake claims that a dye is organic, thinking it means it is a plant-derived dye when in fact it is not. Dye sellers sometimes purposefully exploit this confusion.

Jacquard pre-reduced indigo is available through Amazon, as well as other sources; a supplier on Amazon currently selling Jacquard pre-reduced indigo, “The BT Group”, provides misleading information claiming that what they are selling is naturally occurring. There’s an issue with resellers on Amazon, which can post wrong information about their products; it’s likely that The BT Group doesn’t know anything about what they are selling, and merely selected several phrases from the Jacquard copy without paying attention to how they have changed the meaning by omitting a key word. Similarly, Etsy sellers give blatantly false information about whether the pre-reduced indigo dye they sell is from natural sources, when what they are selling is obviously synthetic, given their suppliers.

Earth Guild makes an error, showing instructions for using natural indigo on a page whose title is “PRE-REDUCED INDIGO INSTRUCTIONS”, but I don’t think that the title of a web page amounts to a claim, given that many people who edit web pages don’t even know how to alter the titles of their pages. (source) In corroboration of this interpretation, they have a page on Lanaset dyes with this same webpage title, so it’s just a mistake.

George Weil helpfully says that pre-reduced indigo is used as “an alternative to Natural Indigo”. (source)

There are blogs that have instructions for using pre-reduced indigo which assert that the dye is natural, but in every case it seems that the blogger was insufficiently knowledgeable. Since they’re not selling the dye, they’re not legally liable for their claims in the same way that someone who is selling a pre-reduced indigo is.

If you find any additional information, I will be interested in learning about it!

(Please help support this web site. Thank you.)

Paula

looking for a light-fast dye or pigment with peak absorption centered between about 570-590 nm

Dear Paula,

I came across your website on dyes, it’s great! Currently, I’m experimenting with an idea to understand how insects see color in plants and how it may relate to a decreased use of pesticides. Something that we all may benefit from. In this, I’m looking at a light-fast dye or pigment with peak absorption centered between about 570-590 nm. The narrower the absorption band the better, and the lower the fluorescence quantum yield the better (for a controlled experiment on absorption).

The material substrate is polyurethane or other plastics. Would you know some dyes that would fit the mold?

Thank you!

Keenan

Hi Keenan,

You want a dye that absorbs in the orange range, which means you want a dye that looks blue. To help with visualizing this, let’s look at a graph I happen to have handy, which shows the absorption spectra of a number of dichlorotriazine dyes that are popularly used for hand dyeing:

absorption spectra of a number of dichlorotriazine dyes that are popularly used for hand dyeing CLICK TO SEE FULL SIZE

(Image provided by Olli Niemitalo.)

The closest of this range (which is not suitable for your substrate; I’m using it only because it is handy) is Procion Blue MX-7RX, which is Colour Index Reactive Blue 161. Its peak is not as sharp as you’d like, anyway, as it absorbs pretty significantly from 530 to 640 nm. Procion Blue MX-7RX is notable for a deep violet-blue color. It is also noted for being quite poorly lightfast when used on cotton, though its lightfastness is significantly greater when it is used with an acid dye recipe on silk.

Dyes that have narrow absorption ranges are unusually clear and bright in color. Wider absorption ranges result in duller colors. A dye that has a very narrow absorption range cannot be used to produce a dark color, no matter how high a concentration of it is used, because it allows most colors of wavelengths to be passed freely. Your desired dye will be a very bright, clear blue, on the violet side of blue, since it will not absorb any wavelengths in either end of the spectrum. You do not want a dye whose color is described as a navy blue, because navy blue dyes always absorb over a wide range of the visible spectrum. You may want to look for a blue dye whose name includes the words “brilliant” or “bright”. There are many dyes that are of a medium royal blue color or of a cyan color, or of a reddish violet, but violet-blue dyes are far rarer. Of course, it is no use to look at dyes that are composed of mixtures of other dyes, as these will always tend to absorb a winder spectrum.

The one person I know who has made a great study of blue dyes is Dr. Steve Mihok, who looked at dyes that attract tsetse flies when used in fly traps. You can see his descriptions of many blue dyes using the Internet Archive (his original site appears to have been taken over by spam and no longer contains useful information). See his page “Blue Dyes” at the Internet Archive, captured in January of 2012.

Mihok concentrated on metal phthalocyanine dyes, which tend to absorb in a turquoise-blue range, I’d say around 600 to 700 nm. My one example dye which absorbs near your target, Colour Index Reactive Blue 161, has as a chromophore a triphenodioxazine structure, I believe. It would make sense to look for a dye with this same chromophore. Following is an image of Direct Blue 106, as an example of the triphenodioxazine structure:

an image of Direct Blue 106, as an example of the triphenodioxazine structure


Unfortunately, the large size of this chromophore may make it unsuitable for use in plastics. Disperse dyes are typically relatively small molecules. The 2003 book “Industrial Dyes: Chemistry, Properties, Applications”, edited by Klaus Hunger, says, “Like phthalocyanine dyes, triphenodioxazine dyes are large molecules, and therefore their use is restricted to coloring the more open-structured substrates such as paper and cotton.” (page 112) I suspect that this leaves you having to find an antraquinone dye. Anthraquinone dyes include many popular blue dyes, such as Procion Blue MX-R (reactive blue 4) and Remazol Brilliant Blue R (reactive blue 19), and many violet dyes, as well. This is disperse blue 3, an example of an anthraquinone dye:

disperse blue 3, an example of an anthraquinone dye

It is important to consider what class of dye you need. Different materials require different dyes; for example, a dye that works on wool is unlikely to work on cotton, and dyes that work on either cotton or wool will not work on polyester, but wool dyes will work on nylon. You say that you want to color polyurethane or other plastics. Polyurethane is quite different from PET plastic, in its dyeing properties, which in turn is quite different from nylon plastic. Although no acid dyes work on polyester (which includes PET), acid dyes can be used to dye polyurethane, though with varying degrees of washfastness. The most washfast acid dyes to use on polyurethane would be metal complex acid dyes. Disperse dye, which is used on most synthetic fibers and is the only option for dyeing polyester, can be used to dye polyurethane, but the washfastness is poor, and the heat required may damage the polyurethane.

It is probably best to dye polyurethane in liquid form before fabricating it into objects. Solution-dyed plastics tend to be more resistant to both light-faging and wash-fading than fabrics dyed after manufacture. This is the explanation of why, for example, Sunbrella brand acrylic fabric is so resistant to fading that it can be used in outdoor furniture that retains its color even after extensive exposure to run and rain. I imagine that you would use a solvent dye for coloring the liquid plastic before using it in manufacturing. Solvent dyes are not soluble in water, but are soluble in organic solvents. Many disperse dyes, which are used with special carrier chemicals to dye polyester fiber after manufacture, are actually identical to solvent dyes.

To color the widest range of already-manufactured plastics, I’d suggest you concentrate on disperse dyes, especially since washfastness is not as much of an issue for you. They will work on nylon, polyester, and polyurethane. When dyeing polyester it is generally necessary to use boiling temperatures and an additional carrier chemical; when dyeing other plastics, the carrier chemical should be omitted, and lower temperatures may be adequate, though the water must still be very hot, at least abot 60 degrees C. Nylon can be dyed at lower temperatures than polyester, and I think the same is probably true of polyurethane as well.

Sourcing your blue dye is an issue. You will note that many textile dyes are sold in the form of in-house mixtures, whose constituents are not made public. Dyes obtained from chemical suppliers tend to be much more expensive per gram, perhaps with greater purity, prohibitive for dyeing large quantities. Textile dye suppliers such as PRO Chemical & Dye and Aljo Manufacturing sell dyes in useful quantities for hand dyers, often at much better prices, but in some cases the generic identity of dyes is not made clear, and many dyes are sold as mixtures in order to produce specific colors. I have listed a number of disperse dyes that are used for hand dyeing in a large chart on my page, “About Disperse Dyes”, at
http://www.pburch.net/dyeing/disperse_dyes.shtml , including disperse blue 3, which is described a sky blue and is sold by Aljo, and disperse blue 56, sold by ProChem, which is described as royal blue; disperse blue 60 is described as turquoise, so its absorbance is probably at a greater wavelength than you want, and disperse blue 281 is described as navy blue, which would have far too wide an absorption band to suit you.
Sigma Aldritch sells Disperse blues 1, 3, 14, 27, 35, 56, 60, and 124. All of the ones whose structures are indicated on their web site are anthraquinone type dyes. I suggest that you contact Sigma Aldritch and ask about the absorption spectra of all of these dyes.

I’ve been discussing only dyes, but you did mention pigments as an alternative. Pigments differ in that they do not bond directly to a substance, but instead are glued to it by some sort of binder, or they can be incorporated directly into some materials. Pigment dyes are pigments whose binder systems allow them to be applied in much the same way as dyes. Unless a pigment is sold with a Colour Index number, it probably consists of a mixture of more than one colored substance. The only pigments I would recommend you look at would be those sold by a chemical supplier such as Sigma Aldrich.

I am very interested in your project and would appreciate it if you would let me know more about it in the future.

For more information, see the following pages:

About Disperse Dyes

Dyeing Polyester with Disperse Dyes

What to Use to Dye White Polyurethane Foam, December 19, 2007

Steve Mihok’s Blue Dyes, captured by the Internet Archive on January 24, 2012

Sigma Aldrich

Lightfastness of Different Types of Dyes

(Please help support this web site. Thank you.)

Paula

Do turquoise acid dyes contain chrome?

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.

Lanaset dyes
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.

copper-based dyes
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.

safety
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.

(Please help support this web site. Thank you.)

-Paula