I went over the stamp with blue sharpie and wet the leather with water and a small amount of isopropyl alcohol. When you compress the stamp into the leather with a press the alcohol reactivates the ink in the recesses.
I've made a couple of stamps (my maker's mark and an icosahedron (d20), mostly for accents on a project I was working on at the time), but nothing this ambitious. I can't get over how nice the texturing came out; well done!
It's just a 3mm thickness disc with the picture on the top at 2mm. I use a 6 ton shop press to compress it with a 1" steel plate used to distribute the force. The print is a no name brand black PLA printed at 0.2 at the fast setting on an AnkerMake M5. You can also see the residual ink, the stamping only takes a small amount. I did a few at one time without having to reapply.
For sure. I just dragged and dropped the jpg into 3d Builder. That program is rudimentary but if it is a simple drawing it does a great job creating a model.