Black Sea Glass is actually Green
backlight shows green color and bubbles
~ submitted by Art in Holmdel, New Jersey, USA
I took these photos at noon on a sunny day with my Sony digital camera. Added Notes:
I used a lampshade in the absence of a lightbox.
Most glass that looks black is actually a very dark green or brown. ~ David from OdysseySeaGlass
"Black Glass" can also be of a different very dark color, even dark red or purple.
In some cases, as in some wire insulators used on telegraph and electric power lines, the glass is actually black.
Dark green, though, is the most common color that looks black in normal light.
Green is caused by iron present in the sand used to make glass.
Iron is cheap and easy to mix in when making glass and has qualities that enhance the glass.
So, for the reason that green glass was cheap and strong, that coloring was used for many bottles and other glass objects where color was not of primary importance.