Here’s the process I used to weather my Abyss Watcher jacket. I bought budget upholstery leather from ebay, which was close to the right color, but unfortunately turned out to be more glossy than I wanted. This process got rid of the glossy coat, darkened the color a bit, and also gave it a more worn appearance. I’ll show the final result later this week!
I recommend either doing this outside or wearing a respirator, as some of the chemicals release fumes that probably aren’t healthy to be breathing in. Nitrile gloves are also a plus. Rubbing alcohol and acetone in particular severely dry out skin (that’s why they work well for weathering leather :-P).
1) Apply isopropyl alcohol (IPA, aka rubbing alcohol) to remove the gloss coat. I squirted it on liberally and then rubbed it off with a paper towel. You’ll need to rub the leather quite a bit to remove the gloss coating, adding more IPA as necessary. If you want a more harsh effect, you could use acetone (found in nail polish remover) instead of IPA. Acetone tends to leave a residue, so you’ll probably need to use IPA afterward. The leather should have a dull, matte finish after this step.
2) Use shoe polish to both darken the leather and to simulate dirt and grime. Shoe polish comes in a variety of colors. I used black, but what color you use depends on the leather. Again, I rubbed this on with a paper towel. I focused more around seams and areas that might accumulate dirt with use. I also made random speckles and streaks. Be careful not to buff the leather too much, since this will make it shiny again.
3) Lastly, apply a leather conditioner. I used Pecard’s leather dressing, but there are a variety of different types out there. This serves three purposes. It moisturizes the leather again, since IPA/acetone dry it out, extending the lifetime. It tends to darken the color slightly, and it also keeps the shoe polish from rubbing off. Wipe on a thin coat, being careful not to buff too much if you don’t want a shiny finish. It takes a while for the conditioner to dry, maybe an hour or two. If, after that, it’s still feels kind of oily, you can wipe off the excess conditioner with a rag or paper towel.
4) Update (optional step not pictured) - After making this tutorial, I also applied some fake black dirt (Ben Nye character powder, Charcoal), which helped remove even more of the shine, darkened the leather a bit, and gave it a more grimy texture. This powder comes in three different colors, ash (white), prairie dust (brown), and charcoal (black), so there are a lot of options for getting different effects. It washes off with water, so if you apply too much or get it on your clothing, it’s not permanent. This also means that it does rub off a bit. I haven’t tested this yet, but it seems like it should be fine for a day’s wear, but you might need to reapply if you’re wearing for multiple days at a convention.
And you’re done! You may want to repeat some of the above steps if you’re not completely satisfied, or it’s still too shiny. I’ve also heard of people using sandpaper to scratch up the surface, but this damages the leather and didn’t quite give the appearance I wanted for my project.