A raw canvas should be sized with Gamblin PVA Size before applying Oil Ground or oil color.
Conservation scientists recommend painters use neutral pH PVA size canvas and paper instead of rabbit skin glue. PVA Size provides a stable size layer that seals the canvas but does not swell or shrink like rabbit skin glue goes. This is because PVA size does not re-absorb atmospheric moisture.
Gamblin PVA Size is made from PVA that is free of animal byproduct, has a neutral pH, and does not yellow. It also retains its flexibility and does not emit harmful volatiles.