[drcy]

Black light identifies alterations in that added material (such as in restoration) will often fluoresce differently under black light. It's very effective for large items such as posters and paintings, but likely less effective for small items like cards because they are small.

It's used to identify modern reprints and forgeries of paper items, because modern paper often fluoresces very brightly due to chemicals added to Post WWII paper. One key is you can identify a modern fake even when you are unfamiliar with the genre (fine art, Civil war memorabilia, silent movie programs), because you can tell the paper is too modern. You may know nothing about WWI history or memorabilia but can identify a modern reprint of a WWI pamphlet or poster with your $9 black light.

Black lights actually test the atomic makeup of the material-- the frequency and intensity of the light given back is determined at the atomic level. It's just that colors and intensity are simple to interpret by anyone. You don't have to be a nuclear physicist to know that modern paper will often fluoresce brightly or that genuine antique vaseline glass is supposed to fluoresce bright yellow green.

Another big thing to look at is gloss. Added materials and reprints will usually have a different gloss and authentic gloss is one of the hardest things to reproduce. Some forgers will try to mask alterations (such as to make rare variations) by 'varnishing' the entire area, but the varnish will make the entire card different in gloss than the other cards in the issue. And if you're adding materials, such as glossing the entire card, you're also going to be simultaneously changing the black light fluorescence.

This is why it's recommended to remove a raw card from a penny sleeve or top loader before purchase. Because even a penny sleeve can hide and alterations that will be noticed when the card is held at a sharp angle to raking light. Holding the card at an angle you will often be able to see any added coloring or materials. You can often see black pen marks on a 1971 Topps upon close inspection, but they may be hidden when in an album or holder.

Major alterations to large items, such as posters and paintings, are usually easy to identify, often including just by the naked eye. Holding an item up to a bright light (the 'see through' test) will reveal many alterations, including added ink or paint. It's a good way to identify reprints, when comparing it to a known genuine card.

Infrared viewers are also used to identify alterations-- infrared is a different frequency of light than ultraviolet (black light), so you get a different viewpoint. But a black light is usually more than enough for collectors and I think much more useful. I don't think anyone on this board needs to go out an get an infrared viewer.

Most 'forensic light' examinations are giving you looks at an item that the naked eye can't see. IR and ultraviolet tests look at an item in lights invisible to human eyes, and microscopes give you enlarged views you can't see with naked eyes. Gloss, which actually is a sophisticated if simple test, is something the naked eye can see, it's just that collectors have to reminded to look at it. Taking a card out of a holder and looking at it at a sharp angle is done with the naked eyes.