We tend to forget that paint on a shelf has a relatively short life. When stored properly, paint in an originally sealed container can be used at least until the date indicated on the packaging. Once opened, its life depends on the storage conditions. If the paint has not been thinned, it can generally be stored for up to 5 months or thereabouts, but you should always first check if it is still usable before starting the paint job.
If there is a soft deposit at the bottom, or a layer of liquid has separated at the top, this is normally not a sign of inadequate quality. It just means that the paint should be stirred thoroughly before using it. If the paint is dried on the surface or at the edges, and caked fragments drop inside from the lid as it is opened, it can easily be strained. A can with a bulging lid is not cause for concern; some care is required when opening it, but the paint itself is usually still in good enough condition. However, if you notice lumps in the paint or if it thickens when stirred, this means that the paint is no longer fit for use. When using wall paint, pay special attention to the smell and appearance of its surface. If you can detect the unpleasant smell of spoiled paint, or a brownish yellow liquid has separated from it on the surface, the paint is infected and should not be used.
Old paint that can no longer be used or passed on should be taken to a hazardous waste collection point in a tightly closed container, or you can wait for the next hazardous waste collection, which is normally scheduled once or twice a year in every town. Until then, it is important to store the paint in a tightly closed container in a place out of reach of children. Also, waste paints should not be mixed together, as this could cause an unpredictable reaction between the different substances.
Coatings containing organic solvents in a liquid state that should be delivered to an authorised collector in sealed packaging are to be distinguished from Environmentally friendly paints and coatings based on binders dilutable with water. In such a case a container with just a thin layer of paint at the bottom may be left open until the paint has dried up completely. The dried paint can then be scraped off with a spatula and disposed of in general household waste, and the empty container can be taken to a recycling point.