Green

Being somewhat preoccupied with optical matters at the moment - of which fuller report in due course - I was struck yesterday by the deep green colour of flesh pressed against the thick glass dividing the standing area in a tube train from the seating area. A young white lady who had her normally coloured bare arm pressed against the glass, with the sausage shaped area of contact being a sort of drab but dark green, perhaps olive green. The rest of the arm, the skin not in contact, was a little darker seen through the glass than otherwise, but certainly not dark green. Was all this a trick of the light, with the lights used in Victoria Line tube trains sending out light with a curious spectrum or was this a trick of the skin, reflecting more green light when pressed against glass in this way?

I tried to repeat the experience using a thick, round piece of glass I happen to have in the study. Quite probably once intended for some serious technical or scientific purpose, quite probably originally from a house in north London.

Pressed against the flesh of upper arm or upper leg, no green to be seen at all. And in any case, difficult to photograph. 

But simply placed on a white surface and illuminated with the study table lamp, there was a suggestion of green, as snapped above. Perhaps at least part of the story is that some glass at least tends to absorb red and blue light, a tendency which gets more visible as the glass gets thicker.

Illumination a mixture of daylight from a south facing window, the sun being in the east, and lamp light from the table lamp. The lamp in question being round with a bayonet fitting, but made in China, an opaque, matt white finish to the lower half of the bulb and probably something more complicated than an incandescent wire filament inside.

PS 1: Bing seems to understand the question about why glass can look green, turning up reference 1, a glass wholesaler in Nigeria. The answer there being that it is all down to iron being added to the glass. While from reference 2, another glass wholesaler, this one from South Carolina, we get much the same answer and the snap above. Further surfing indicated.

PS 2: more particularly, Bluffton in South Carolina. A place on the edge of the sea, in the midst of lots of waterways and islands. Probably all very scenic if the snap above is anything to go by - and probably much too hot in the summer for my comfort. Perhaps once islands where the language retained more traces of African languages than you get on the mainland. About which I read not so long ago, but am presently having trouble tracking down.

PS 3: a little later, I ask the blog and come up with reference 3 in no time at all. The problem now is that further search has failed to turn up the pdf mentioned there, which I probably did not do much more than glance at, at the time, back in 2019.

PS 4: a little later still. I ask DPLA for another copy and after a few tries get there. Now properly catalogued and filed so it will not go missing again. Perhaps the first copy was cleared out of the Downloads folder in one of my occasional fits of housekeeping. Perhaps, back in 2019, 75Mb seemed a bit strong. Doesn't seem to matter now.

References

Reference 1: https://glass.com.ng/glass-sometimes-appear-green/.

Reference 2: https://www.bottlesupglass.com/why-is-glass-green/.

Reference 3: https://psmv4.blogspot.com/2019/03/gullah.html.