I do pyrography on lots of surfaces, paper, wood, leather, canvas etc.. I use a Razortip. Burning leather is all about temperature. I start at a low temperature to do layout, then as I fill in the piece I go back and keep working the shading. I suggest using a scrap pieces to get your temperature ranges you would like to use. When you start to work a project keep a scrap piece handy. Before putting tip to your project run it across the scrap to pull of some heat from the tip to eliminate the chance of small burn marks. Also keep your tip clean, leather dirties the tip quickly. When you do your practise work on scraps try the product you plan on finishing with. I use mink oil paste on most of my work. Depending on what you use you my find you need to darken your overall burn so as not to loose the detail in the burn if the finish darkens the leather.