Originally Posted by
ccdjg
Yes, this is correct, although it is not fibres that show up, but the whole paper area that is not covered by print.
Before 1950 no paper was ever pure white. After 1950 the paper industry begain to put substances called optical brighteners in paper, which gave a very bright white appearance and after 1955 up to the present time virtually all paper has contained these. The interesting thing about these brighteners is that they are very easy to detect. All you have to do is shine a weak uktraviolet light on the paper, preferably in the dark or low light conditions, and the paper glows a brilliant blue. Paper that does not contain these additives just looks dark. This phenomenon is used as an anti-counterfeit measure for banknotes - real banknotes are printed on paper that does not have any optical brightener in it. Such paper is extremely difficult to source these days, so counterfeiters are often forced to use ordinary brightened paper. This means that most counterfeit notes will glow blue under ultraviolet light whereas a genuine note won't.
So you can assume the following:
1. Any printed literature or box label that DOES glow blue under ultraviolet light CANNOT POSSIBLY date from before 1950.
2. Any printed literature or box label that DOES NOT glow blue under ultraviolet light MOST PROBABLY, but not necessarily with absolute certainty, will date from before 1955.
I have used this technique several times to authenticate air pistol boxes and airgun literature. In particular one very convincing box claiming to be original to a pistol made in the 1920's was shown to be a fake by this method. This helped prevent an incorrect historical record being made, as a box for this particular pistol has never been reported before. Unfortunately it came too late to help the owner, who had paid a high premium for the box some time before.
In case you think ultraviolet testing might be too expensive for the average collector, note that you can buy perfectly adequate ultraviolet pens off fleabay for one or two pounds.