Longevity of original works

Most original works use different pigment and dye systems to reproductions. Very much it is the type of media (e.g. paint, watercolour, ink, etc.) as well as the preparation of the substrate it is applied to, which has a large bearing on the aibility of the artwork to withstand environmental factors.

The biggest challenges to longevity include sunlight (UV in particular), humidity (and moisture and mould), and airborne pollutants (though geothermal areas are often rich in acid gases which can attack artwork). Proper hanging location, controlling the environment if possible, archival coatings, and protective framing can significant help increase the longevity of your investment. Most modern museums control all of these factors.

Most artists use quality substrates - e.g. properly primed canvasses or boards, acid free archival papers, etc. though there is no real way that the purchaser can know this without speaking to the artist.

Most quality media come with light fastness ratings. Traditional earthy colours tend to be quite stable with respect to fading. However there is no way for a purchaser to accurately or reliably determine if brighter colours in a piece may fade - for instance some red pigments are prone to fading while others are extremely stable. The true is the same of many other colours. However there a few colours for which stable pigments have yet to be found - for instance fluorescent colours, and most bright fuchsia/rose pink colours are considered fugitive and at high risk of fading.

Dyes can be more prone to fading, though many earth colours and india ink are very permanent. Charcoal and graphite sketches are almost immune to fading, though yellowing of the paper they are on may be more of an issue.