Nothing, really. As long as you keep the painting protected. I have oil on canvas paintings that my distant relative painted about 80 years ago still hanging in my home. My family has taken care of them, though. Some general things you should keep in mind are not to take it out of the frame too often. Dust and other air-borne pollutants can affect the color and integrity of the paint. Also, harsh lighting and extreme temperatures and fade or crack the paint. Just take care of the painting, and it will be fine.
Acrylic paint is the best choice for creating handprints on canvas because it is easy to work with, dries quickly, and provides vibrant colors that will last a long time.
Star with a well stretched canvas. Gesso or prime the canvas. Place your painter's tape firmly on the surface of the canvas. With the edge of an old credit card, carefully press the edges down. Do not over stretch the canvas or damage the surface. Apply your paint from the tape to the canvas (NOT from the canvas to the tape) give the paint time to set up but not dry completely. Remove the tape in a slow steady movement pulling down and toward the painted area... do not allow the tape to sag and mar the fresh paint or leave wet paint in undesireable places. Allow the paint to dry completely.
Picasso spent most of his time painting actual canvas paintings.
It depends on the paint used. "Luminous" paint will only last a short time because it will lose its chemical reactants (radioactive paints being unusual). "Phosphorescent" paint may absorb light energy, then release it again. This will last for a considerable time but not for any great numberof years, because it reacts with other chemicals as well.
No, however, if you fold up the canvas for transport, there is a good chance that it will "block" which is where two painted surfaces adhere to one another even though they have had sufficient dry time.
He, like all painters at the time, used oils. He also sketched in pencil and whatnot.
Oils paints can take a long time to dry enough not to smudge. Though a skin quickly forms on the surface, thick paint may still be soft beneath, even months later. Only time will ensure the paint dries right through to the canvas. If for children, I would consider using acrylic paint, which dries very quickly.
When paint reacts with oxygen, a process called oxidation occurs. This causes the paint to dry and form a hard surface. Over time, this reaction can lead to the paint chipping or peeling.
The paint that should be used on a gym floor is an oil based paint. This paint adheres best to the surface and lasts a long time.
Nothing bad happens.
It takes a long time for wet paint to dry. If you sit and watch the paint dry, you will be sitting there for quite some time without really accomplishing anything useful. It is a waste of time.
so the paint wouldn't need to be done again for a long time