Editing Ultraviolet (section)

==Degradation of polymers, pigments and dyes==
{{main|UV degradation}}
[[File:Failedrope1.jpg|thumb|left|UV damaged [[polypropylene]] rope (left) and new rope (right)]]

[[UV degradation]] is one form of [[polymer degradation]] that affects plastics exposed to [[sunlight]]. The problem appears as discoloration or fading, cracking, loss of strength or disintegration. The effects of attack increase with exposure time and sunlight intensity. The addition of UV absorbers inhibits the effect.
[[File:IR spectrum carbonyl.svg|thumb|upright=1.15|IR spectrum showing [[carbonyl]] absorption due to UV degradation of [[polyethylene]]]]

Sensitive polymers include [[thermoplastic]]s and speciality fibers like [[aramid]]s. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength.{{cn|date=May 2024}}

Many [[pigments]] and [[dyes]] absorb UV and change colour, so [[paintings]] and textiles may need extra protection both from sunlight and fluorescent lamps, two common sources of UV radiation. Window glass absorbs some harmful UV, but valuable artifacts need extra shielding. Many museums place black curtains over [[watercolour painting]]s and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV. Various forms of [[picture framing glass]], including acrylics (plexiglass), laminates, and coatings, offer different degrees of UV (and visible light) protection.{{cn|date=May 2024}}