From the manufacturer:
Gamblin Gamvar saturates and gives greater depth to the colors in your painting and gives your work a unified and protective semi-gloss surface. Developed in collaboration with the National Gallery of Art, Gamvar goes on water-clear, stays water-clear and can be easily and safely removed with Gamsol. Gamvar is virtually odorless and ready to apply. For most paintings, there is no need to wait 6 to 12 months before varnishing with Gamvar. Gamvar can be applied when the thickest areas of your painting are thoroughly dry and firm to the touch.