I became a member of Leatherworker.net a few years ago but forgot about it and this is the first time I´ve asked a question. Thank you all so much for your answers, I didn´t expect that much. Sorry if I use the wrong words for the technical terms as English is not my first language, don´t hesitate to correct me.
A while ago I was able to buy 12 hides of cow leather for a very good price and that is what I want to use. It´s dyed brown, it feels quite oily and the surface is rather water resistant so it´s not so easy to affect it. I have tried oxalic acid, aceton and chlorine so far. I will experiment with your suggestions and see what happens. My inspiration for the look I want was an episode of the TV show Project Runway (s10 ep 13). A participant made a leather skirt that he accidently spilled bleach on and it gave the leather a really interesting look. That leather was of course nothing like the one I´ve got.