Opal glass looks very different depending on how it's lit. The full opal
effect comes when light bounces off the glass to the observer; when
backlit, the glass is a sickly amber.
Overhead-Right
On-Camera Flash
Flashlight Beam
Opal comparison: Fry, Locke (Corning),
Hemingray.
The Locke was found in a bucket with a bunch of junk glass by a lucky
California collector who brought it to Auburn for show & tell (and sale,
if you had enough zeroes). The author brought his Fry and Hemi opals
for comparison-- the Locke glass is quite different! Streaky and
experimental-looking compared to the polished Fry, it was made under
contract in the 1910s by Corning using Locke's own glass patent.