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