It's best to also make sure the painting surface and material that's been painted on (such as canvas) is protected from touching anything acidic. The safest is to stand the paintings up, for example on drying racks, and cover loosely with acid-free sheet of paper between pieces. Do not stack paintings on top of each other or underneath heavy items as their surface may bind or create pockets of moisture which might introduce organic growths (i.e. damaging fungus or mold).
