A quick technique that works is after the color coat of black is down as your base ...usually a dark black-gray. Then you can dry brush with brown for edge wear. Depending on type of leather wear you can use two different tones of leather brown---Vallejo is a good brand to use.
Then a wash with a pure black. The best results are when you combine the two methods to get the look you are looking for.
I suggest you base with either lacquer based paint or a acrylic sealed in with a decent top coat. So if you make a mistake you can clean up and then start again...Especially if you are dry brushing with water based Vallejo. .THEN seal that work in & then final wash with enamal OR water color wash &clean up w/ Minerla spirits or water??
HTH
Stev,e