I was wondering if there was some easy way to darken some scrap brown leather that I'm using for my Sparrow glove. Ideally, it would be something I rub onto the leather instead of something like a dye, so that I can darken some areas more than others to make it look well-used. I'm not positive, but I believe it's full grain or possibly top grain (I've only read definitions, and haven't had the experience to tell for sure). Any ideas?