Sealing/Protecting Glass…?

I am trying to find something that I can protect or cover glass that I’ve put rub-on transfers on. I have a business idea that will be selling vases that I’ve embellished with rub-on transfers, yet I do not know how to seal or protect the rub-ons so that customers can wash the glass after use. Any ideas or will this be more of a trial and error type of thing?