You’re striving to keep the surface free of contaminants, especially
moisture. There are several ways this can be done. I’d suggest
browsing jewelry supply catalogues and reading the advertisement, and
browsing the internet.
Whatever you use, consider the difficulty in removing what you have
put on. Remember, what you sandblasted off was there to protect the
surface, you don’t want to sandblast the next coating off. Wax may
work, a light coating of oil may work, etc.
Work on it and you’ll get an answer.