Cloth headgear cleaning method

[Michael Stern]

I have a black overseas cap that was supposed to be 100% authentic. I was told to give it a test using a black light. Upon performing this test, the fiber seemed to glow in spots. I questioned the former owner about this, and he told me that he attempted to clean the hat some years ago using a cleaning agent containing a phosphous chemical. It sounded a bit strange, but thought I would ask if anyone ever heard of this before?
ms

[BenVK]

It's not uncommon. A lot of modern detergents will cause fabric to glow under a uv light.

The only way to be sure of the cap is to post some pics so you can get some opinions.

[Michael Stern]

Cloth headgear cleaning

Thanks Ben,
I appreciate your quick response.
Mike