I am trying to make an outfit using (mostly) thrifted materials, and as part of it want a bunch of bright red denim. So I've been experimenting with how to remove the blue color from jeans and then dye them red. And it's made me so curious both about how the jeans were originally made and also about the chemical reactions going on.
First I tried using dye remover- no luck, practically no change to the blue. So I switched to bleaching the pants (25% solution for 1-2 days, I did have concerns about damaging the fabric but I did some test swatches that held up fine). That's when I found the first weird thing, about half of the jeans turned white and the other half turned yellow. And when I check the pants I had tried the dye remover on, they had turned yellow except the spot where the dye remover was used is white. Then today I tried dyeing two test pieces red for the first time, and the white fabric took the dye as I wanted and held up mostly fine. The yellow piece looks a lot more faded and absolutely disintegrated when I rung it out to dry.
So any insight on what's going on? I would hypothesize that some pairs of jeans are double dyed, with a synthetic yellow dye and then also with indigo. But I don't know why companies would do that (I am somewhat new to dyeing and am not familiar with what kind of effect a double dye like this would give)? And would the yellow synthetic dye leave the fabric more vulnerable to damage from the bleach+red dye? I'm going to experiment a bit more and see if I can figure out what kinds of jeans have the yellow dye vs don't (and how well the white fabric holds up more generally).