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I read on https://smile.amazon.com/gp/product/B07XP321LY/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 (mirror):

Black glue umbrella is the newer version sun umbrella instead of silver glue umbrella. Our XUYAO sun umbrellas are coated with triple (3x) black glue, providing UPF 50+ highest UV protection, blocking UV-A 99.99%, blocking UV-B 99.99%. And the black glue are coated inside where is safe from rain-washing, providing lifetime UV protection.

Can using black glue coating on an umbrella block 99.99% of UV-A and UV-B radiations?

I couldn't find anything when searching for "glue coating".

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Simple answer - YES

More complicated answer - anything, with enough layers can block UV rays to such extent.
UV are waves. 315- 399 nm for a UVA and 280-314 nm and UVB in wavelenght. So using a losesly knit clothes leaves the opening for the wavelength to go through. Stacking layers on top of each other make the opening smaller and smaller. WHO Individual protection against UV clothing

Most complicated answer - it's not the matter of material but it's color. Difference beetwen silver and black glue is just hue. The darker the hue (of anything beetwen you and sun) the more UV rays are absorbed.
Darker the color the more wavelentght is absorbed and not bounced back. Which color reflect more light

There is a diffrence beetwen "Blocking" and "absorbing" but in the marketing world what is important is how to sell you the final amount that get to your skin.

There is some miscomunication in the text you quote, as "what is silver glue umbrella"? Do they compare to single sheet of fabric single coating with silver glue or a "sandwich" umbrella where you have two sheets of material and glue beetwen them (and such umbrellas provide 100% UV).

Additional info

Unfortunately, an international standard for the concept of the UPF has not been developed yet.

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    Please provide some references to support your claims. – Oddthinking Jan 23 at 13:18
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    You haven't shown that hue is relevant. You haven't shown that this umbrella (or any umbrella) reaches 99.99% (or even UPF 50+) This isn't an answer. – Oddthinking Jan 23 at 13:51
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    Darker colours only mean that more of the visible wavelength is absorbed. That link you've provided doesn't suggest anything about light outside of the visible spectrum, where UV radiation falls. – JMac Jan 23 at 18:06
  • Hue is definitely a red herring, e.g. en.wikipedia.org/wiki/Zinc_oxide#UV_absorber is incredibly common in sunscreen and white in the visible spectrum. Reflectiveness should be perfectly fine for blocking, the concern should be penetration through the fabric, not absorbtion vs. reflection. – Jack Jan 23 at 23:07
  • Yeah, visible hue has absolutely sod-all to do with ultraviolet absorption or lack thereof. It's theoretically possible to have a material that's entirely black and opaque to the visual spectrum yet perfectly translucent to UV, and vice versa. – Shadur Feb 8 at 10:31

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