Light-oxidized Vat Dyes
Ink-o-dye is a type of vat dye which uses light rather than oxygen to 'fix' the dye, with a wide variety of possible effects. These dyes, which are chemically similar to vat dyes, are developed by light instead of being applied in an oxygen-free bath and being developed in the fabric by exposure to oxygen. Ink-o-dyes are true dyes, not fabric paints. A dye itself attaches to the fabric; fabric paint includes a glue-like binder, which imparts a stiffer feeling to the fabric. The process is more difficult than the process of tie-dyeing with fiber reactive dyes. One retail source of Ink-o-dye is Dharma Trading Company.
Solubilized Vat Dyes
It's inconvenient to have to reduce your vat dyes in order to dissolve them. However, it is impractical to sell the reduced form of the dye, because it will oxidize in the air, back to the insoluble form. The solution to this problem is for the manufacturer to convert the soluble leuco acid form of the dye to the leuco ester, such as by reacting the leuco acid with sulfuric acid. The leuco form of this solubilized dye can be regenerated by removing the ester group chemically (with sodium nitrite in dilute sulfuric acid) or by the action of light. The drawbacks of solubilized leuco esters are their greater expense and their poorer uptake into the fiber, which results in paler shades.