Help with maintaining oxidisation in recess

[Susie]

Happy New Year everyone.
I would really like some advice on how to maintain some oxidisation in the recesses of a silver ring.
I made some rings with a deep laser hallmark on the outside and have tried various methods of making it stand out.
Using platinol and also using some stamping ink. Can you advise on the best way to keep the black colour? I'm attaching a photo to show you the ring.
I wondered if there was a liquid sealant i could paint into the recess? The edges of the hallmark are a bit sharp, so can't really use a cloth to rub a waxy sealant into it, so is there a liquid?
Thanks so much for your help. I made a ring for a member of family, and the blank ink i used has already come off. I know this can be googled, but i'd rather get advice from the experts.
sue