help with black light test

[Gregorio Torres]

Could anybody tell me how definitive is the black light test to probe the originality of a cloth item?
What is the reason why a white cloth bright or not with this kind of light?
Why this test can go wrong?
Thank you in advance
Gregorio

[marcus777]

hello Gregorio

From my limited understanding black light test is a useful tool but is not definitive. modern clothes glow underneath black light because of chemical brightens added to modern washing powders and liquids .this means that if something old has been washed with modern washing powder or liquids even just once it will then glow when subjected to black light test even though the item is original. Black light test is useful but not to be soley relied upon,used in conjuction with other ways of ruling something either in or out it is still a handy tool to use.hope that this is of some help.

[Mr. Scratch]

If I recall correctly, the chemical used in modern bleach and detergents is phosphorus, which gives modern white cloth its remarkable (and long-lasting) brightness. You can sometimes tell pre-war cloth that has been laundered post-war as the UV glow is sometimes a bit dimmer and rather more uneven than on modern-made cloth, which tends to glow a very bright and uniform violet.

[phild]

Phosphates are added to detergents as brightners, the general belief is that prior to the 1950s phosphate based brightners were not WIDLEY used in the manufacture (or detergents for washing) of white fabrics or paper. The usfulness of UV light to evaluate pre 45 cloth is not absolute.

Don't bother looking at any other color than white as glow or color changes mean nothing on these other colors, other than what was in the dye.

UV light was a better tool when it first became reconized (early 1980s for me) and before all the fakers took countermeasures.

[Gregorio Torres]

Thank you very much, friends.
Now I know why some originals items can glow with this light, but...
How some fakes don´t glow? Do you know the nature of this faker´s countermeasures?

[joelhall]

simply because they havent been washed or made from the same materials as were used then, materials which have been processed in a similar way.

like others have said this test (in fact any test) isnt definitive on its own. its more a handy guide.