Leather is susceptible to water damage, and can also crack and break if it’s not treated properly. I use a couple of light coats of mink oil to soften and protect it, which is a vital step as my dogs are very rough with each others’ collars (and they occasionally hop in the pool!). The first layer(s) are applied before the finish when the leather soaks it up like a sponge. It darkens the leather a bit (especially initially) but there’s already a noticeable difference in the suppleness after the first application. The excess is rubbed off with a paper towel, which takes the extra dye off with it.
Leather naturally has little fibers that make your edges look a bit frayed and the flesh side look rough. Burnishing is the process of smoothing it out. In this video, I used gum tragacanth to help with burnishing, and it just takes some elbow grease to rub it in for smooth shiny edges and backs. I’ve since moved on to saddlesoap and water, as it allows dye to penetrate through.
Lastly, I finish the leather with a top coat (I use Zelikovitz Professional Top Coat in Satin), which seals the leather. The final steps include attaching rivets, dee rings, and buckles.