Leather darkens with an application of oil. While neat's-foot oil works best and is manufactured specifically to darken leather, you can use good-quality vegetable oil from your grocery store, as well. You can darken any item made of light-coloured leather, from sofas to handbags, jackets and horse tack, with just a few tools and a few hours of your time. The oil also conditions the leather, making treated items more flexible.
Clean the leather with leather cleaner and a rag.
Soak a clean rag or sponge with oil. Rub it evenly onto the leather item.
Remove excess oil with a clean rag and put the item out in the sun to dry.
Apply a second coat to darken the leather even more. Let it dry.
For smaller items, like reins, bridles, or breast collars, put the item into a bucket and leave overnight. Remove the item in the morning, clean it, and let it dry. Good-quality leather soaks up oil more quickly and will have a more uniform look. Applying oil will not produce the same results with fake leather products. Natural-coloured leather will tan naturally in the sun.