The shelf life of artist colours can depend greatly on the conditions in which they are stored and used. If the threads of the tubes or jars are wiped clean so that the lid can be fully screwed back on to remain air-tight, and the materials are not exposed to high heat or extreme cold, then the shelf life will be years.
Schmincke paint laboratories give the following general shelf life expectancies:
Pastels: Pastels have the longest shelf life of all artists’ colours, nearly unlimited when stored in a dry place.
Watercolour & Gouache: at least five years, usually much longer. A dried tube can be cut open and the paint dissolved on the palette as if it were a pan. Old watercolour pans can usually be revived with a few drops of water.
Acrylics: five or more years. These very much depend on proper storage. They must be kept moist by being stored in air-tight containers. They must not freeze otherwise the consistency of the paint will be ruined.
Oil Colour: has a very long shelf life if the tubes are airtight and undamaged. Some pigments can separate from the oil, even over a short period of time, but this is not damaging and the oil is easily mixed back in.
Paper and Canvas: will last forever if stored in a dry place and out of direct sunlight.