Re: bleaching printed cotton

["Mary W. Ballard" <BallardM@xxxxxxxxxxxx>]

Jenny--Vivian has a nice stain removing method there. 1) Sodium dithionite (hydrosulfite) is a reducing agent and will--as Season reminds us--reduce iron to a soluble state, very nice to reduce rust stains on cotton as you use a little alkali as an assist. Please note that sodium dithionite will also reduce vat dyes (like indigo) to a colorless/yellow soluble [bleeding!] state! These can be reoxidized with air; the dye can return--if you haven't washed it away. However, most azo dyes will be split by reduction--and the color will not return. Azo components are often found in direct dyes and in reactives. 2) I was thinking that Jenny would want to test the fastness of the dyes/pigments before using an oxidizing or reducing treatment. 3) If the stain is caused by wood acids, rather than foxing, you might test for acid stability and see if an organic acid--acetic, lactic or citric in dilute solution--would remove the stain. 4) If it's foxing, the colorant is a melanin type and bl!
eaching is necessary to strip it off...best wishes, Mary