Direct dyes on cotton (often azo dyes) tend to bleed in water-found as sometimes faded cotton repairs in tapestries or carpets, red corduroy, etc and perhaps azoic as in batiks, were at one time cleaned with saponins which as not as 'searching' as surfactants. Saponin or its bark form can be expensive if ordered from a chemical supply house.

Soap nuts, grown in Central America, India, and Indonesia, are another source of saponin. They are now available from Lehman's cat # 100-004-356  tel: 800-438-5346 https://www.lehmans.com/  for about $25/pound. A few can be steeped in hot water (as with making tea) and then a portion of the solution is diluted to a very pale shade for use in lukewarm water. The mother liquor with the nuts can be refrigerated for weeks, months in a jar until needed.

Mary W.  Ballard
Senior Textiles Conservator
Smithsonian Museum Conservation Institute
4210 Silver Hill Road
Suitland, Maryland 20746
Tel 301-238-1210 Fax 301-238-3709