Last summer I made some vinageroon for some wood projects. Then, I left it out, in an open jug, until mid-winter. There wasn't a lid, but I had a paintbrush stuck upside down in the opening, which would have kept a lot of the snow out.
When I decided to try it on leather, I went out and grabbed it. -30C outside so I had to thaw it out first.
It yielded a grey instead of black. First, I used a colour dye over the grey, to rescue it. (photo inset/blue with runner)
After some drinks and internal arguments, I must have decided I liked it, because I just made a few more. The fresh batch of vinageroo also yielded grey.
Of course, because of this thread, I suspect tanins, and may soon try tea or tree-goiters to achieve the black I was after. I'll post results when I get that done.
The leather I'm using is a budget-friendly choice, and maybe going cheap means you don't get as many tanins...In anay case, I like the grey so much, I'm starting to wonder what other mistakes I can commit.