community of dyers

About a year ago there was a discussion about the rapid fading of indigo-dyed fabric, particularly along folds and creases. I have been trying to discover why this happens to my silks dyed with indigo. I have used both natural lump indigo and powdered synthetic indigo reduced with hydrosulphite or thiox and also a traditional sig (urine) vat with no added chemicals. Regardless of which method I use the fading occurs over several days with the cloth hung out in my workroom or folded on the work table. It appears to be identical to the fading caused by ozone exposure but I live in the woods in a very rural area. I do have calcium-rich hard water. Did the two Australian dyers ever decide what caused their similar problem with indigo?

Julia in Vermont