What material should I use to protect/ finish my oil painting?

[emily m]

I recently bought two small already painted side tables for my dorm room. I used regular wall primer on the tops then used oil paint to paint a picture on top of the primer. Using oil paints was a first for me and I didn't realize until after I was done that I should have mixed the paint with something first.
Anyway I really like my painting and would like to protect it but still have functioning tables... any suggestions?

 

[XxXmCrXxX]

in my art class we use "workable fixative" to keep it clean so it doesn't rub out and stuff

 

[Jon]

Danmar Varnish is the traditional, but it will yellow over time