Handling The Paintings
Paintings, even oils, are delicate and to be able to enjoy them for a long time must be treated with respect. When I sell an oil painting I will advise on the right varnish to use and when (the paint takes at least 6 months to dry out for varnishing).
Paintings on card
Paintings on card are reasonably robust, but try not to touch the painted surface as this leaves marks and stains which will show up over time.
Paintings on Fabriano
Paintings on Fabriano paper must not be held in one hand or creased. This breaks the paper fibres and weakens the paper. Lay the painting flat to look at it or hold it carefully with two hands to avoid the creasing. The watercolour will be affected by moisture and if kept in direct or even bright light, some colours may fade.
Paintings on vellum
Paintings on vellum must be handled as little as possible. They will not crease, but the surface is delicate. The paint sits entirely on the surface, so it can be completely washed off with water, so keep water away from it at all costs. Modern colours fade less than the old colours, but even so, blues (therefore greens) and anything with Rose Madder will fade in strong light over time.