Re: what is the best Plexiglas?

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Judy,

Let me give you an example. Three years ago I happened to be in the office of the director of our computer services. He had some photos of his children on his desk (don't we all) which had faded considerably. They were ordinary silver/gel color prints (probably Kodacolor) in little glass and metal frames. His office is in the basement of a building and has no windows, but there is a standard industrial-type FL fixture in the ceiling with four 48" bulbs. I asked him how long the photos had been there and he said about five years. The blues were almost gone. Greens very faded. Mostly only red and yellow left. I advised him to have the negs reprinted and get some UV plastic for the frames. He has done so and so far no fading problems.

First, let me say that the dyes are most sensitive to fadeing. This is why normal ink-jet prints are non-archival. Real pigments last longer. Different hues fade at different rates. Different types of pigments fade at different rates. Different types of FL bulbs produce different amounts of UV of different energies, so that is a factor as well.

Second, since pigment fadeing is much slower than dye fadeing, your painting may be fadeing very slowly so that you do not notice much difference. Also you havn't said how big the FL light over your computer is i.e what wattage and how many tubes.

Third, we archivists think in long time periods. i.e multiple decades and centuries, so we try reduce deterioration even though we know it cannot be stopped. Nevertheless, it can be slowed down a lot. I can tell you that knowledgable museum curators do not use flourescent lighting or metal-hallide lamps. No man made UV source is as strong as the sun but there are many man made sources that produce a lot of UV . Arc lights such as carbon arcs and welding arcs produce a lot of UV. So do mercury arc bulbs (found mostly in labs) . These bulbs have a pure quartz envelope which transmits UV. An FL bulb is essentially a low pressure mercury arc but it has a glass envelope which absorbs short wave (read higer energy) UV.

In summary, everything is deteriorating but some things are deteriorating faster than others ;-)

Bob Schramm