Hi @ultravioletmag, nice to see you again!
Varnishing? What do you mean?
I know of some spray fixatives to protect finished drawings, but that should be our last concern.
Anyway, there are some fixing sprays to apply to the finished drawing, but you must take care of their quality so that they do not yellowish later.
Let me know if that's really what you're interested in so I can give you more detailed information.
I really appreciate your interest, so don't hesitate to ask me your questions.
Regards.