Wow, what an interesting thread.
yourmessagesir: would be interested to hear the details...
I will give my opinion on the subject....
I am both a Tattoo Artist and a Leather worker (Scrimshander too).
Leather is similar to human skin but it is dead. When doing a tattoo the artist tries to deposit the ink in to the 3rd layer of skin later to be healed over by the body. The tattoo is then visible Under the skin. If you go too deep the lines (ink) will be carried from the point of origin, this is referred to as a a "blow out". If you go to shallow, parts of the ink will be removed during the healing process.
Leather is Dead. There is no healing process, and it is not translucent, so when you puncture the skin for the most part it the design will only be visible at the point of penetration. Most Veg tanned leathers I have worked with have been dried out during the tanning process and need to be oiled. If the leather is dried out then the Ink would spread or seep from the point of origin. This would also allow staining from the wiping process.
I would think that leathers that have been tanned using wax in the process would be a good source, such as harness leathers, etc..
I just tried some Mop-n-Glow on a piece of veg tan (1 coat) with A&D ointment lightly smeared on top. Did a blot test to see if I could wipe without staining the leather, Good. Then tapped a needle thru another blot and wiped, Good.
So, I will try to Oil the leather let it sit for 24 hr, top coat it with Mop-n-Glow, apply A&D and try a simple tattoo.