It sounds like the people who did this didn't use real leather dye to blacken the engraved areas in the designs, since it's permanent and doesn't rub off. Without knowing what they did use, it's hard to say what might go over the top of it and keep it from doing this. It may be an altogether futile endeavor. You could try some leather sealing products like Resolene, but whether it's compatible with whatever was used is anyone's guess. Here's some deep discussion on the topic on the leatherworker's forum: Sealing Leather After Dyeing? - How Do I Do That? - Leatherworker.net