Name: paulette george
Message: I am a graduate student, I have searched hi and lo for information on if it is possible to directly apply Indigo dye. I would like to use it in silk screening if it is possible. I have tried sodium alge. as a thickener without luck. Please help! 

Indigo dye should be applied in a reduced form, which is called the "leuko" form, because, like all vat dyes, it is only when it is reduced that indigo is soluble and able to get inside a fiber. Otherwise it will just sit on the surface and will not be permanent in the fabric.

I'm not sure how much chemistry you know. "Reduced" is the opposite of "oxidized", in chemistry; a vat dye such as indigo can be converted from oxidized to reduced form, and back again, depending on the chemicals and amount of air around it. Air oxidizes indigo to its insoluble form. The reduced form of blue indigo is yellow in color. The oxidized form of indigo is blue.

Using a dye thickener such as sodium alginate will not help. The issue is the chemistry of vat dyes.

If indigo is applied when it is in the fully oxidized blue form, it will not be able to get inside the fiber and will rub off (in a process called crocking) when dry, and will also wash out.

To reduce indigo, you can prepare a natural fermentation dyebath with bran, or a thiourea dioxide/lye dyebath, or a zinc/lime dye bath. Each of these presents its own challenges. Sometimes you can also buy pre-reduced freeze-dried indigo crystals from Aurora Silk, and it looks as though Paradise Fibers may have it in stock currently. Directly painted indigo, even in reduced form, could end up much less permanently attached than indigo that has been properly applied in a dye vat, depending on how much it gets oxidized before it actually penetrates the fiber. It is best to immerse fabric in an indigo dyebath, as any surface application of indigo is bound to expose it to oxygen, which will convert it to the insoluble form. However, if you are determined to do direct application of indigo dye, there is no question but that pre-reduced indigo is the only way to go. There's just no point at all in attempting painting or silk=screening with oxidized indigo.

Indigotine, also called indigo carmine, is a chemical derivative of indigo which has been treated to make it soluble in water, by adding sulfate groups. It is not used by natural dyers, but it is commercially available as a food dye, US FD&C Blue No. 2, and is labeled E132 in Europe. Unfortunately, the blue food dye you normally find available is US FD&C blue 1, a completely different dye. Like other food dyes, Indigotine cannot be used to dye cotton, because it is an acid dye and cannot attach to cotton, but it can probably be used quite well to dye wool or silk; it will be necessary to steam wool or silk that has been painted with indigotine, in order to fix the mostly hydrogen bonds that hold the acid dye to the fabric. Steaming will not help to fix true indigo to silk or wool, but it will probably work nicely for indigotine.

A more suitable type of dye for silk-screening would be fiber reactive dye, such as Procion MX. This dye, thickened with alginate or another dye thickener, is applied to fabric that has been pre-treated with soda ash. If properly applied, it is extremely washfast and long-lasting. Fabric paint is more commonly used for silk screening, but it is certainly very possible to use the right kind of dye, instead.

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