Hi Nigel
What I described as impurities ( perhaps the wrong word ?) are the few small scattered black specks and small bubbles containing black residues/fragments which can just about be seen with the naked eye
Not visible on the images I sent though—sorry I should have made that clear.
No need to worry about your eyes
Are these black specks/residues, bits of carbon that didn’t completely vaporise during production?
I understand that some of the other big names in glass had similar problems in the 30s—eg Monart, Whitefriars, Nazeing............
Scott