Strange marks

[Dil74]

Hi

Roof lantern - self cleaning glass. These marks (see attached) all over (you may need to zoom in to pics. Advised only soapy water to be used. Any ideas?

 

[Pjj]

Have you tried soapy water what happens ?? Lick your finger and give it a rub does it come off ???

 

[scottish cleaning service]

Looks to me it was painted black decades ago to block out the sun and its deteriorated with the sun?