The more I try to find out about this little 8 sided salt, the more confused I get
It's a fab colour and doesn't need a U.V. light to glow as shown. I would imagine its an individual salt as its only 2¼ x 1¾ x ¾ inches, has what I'd desribe as a square pyramid with a flat square hobnail pattern.
I think it could possibly be one made by Joseph Webb, no. 4775 seen here in their 1870 catalogue http://opensalts.us/References/Catalogs/England/ENG-Webb1870-aW.jpg
(taken from here http://opensalts.us/opensaltsus.html
) although the image is not very clear.
I then discovered that Webb Jr. went to work at Phoenix Glass Works Ohio c.1883, and that they produced Canary Flint or Canary Yellow pieces, so it could have been made there, although I'm inclined to think more near to home, being in the U.K.
Just to confuse things even more, for me at least, other glassworks made similar ones including George Duncan & Sons, which can be seen on the opensalts website in the U.S. section no.308, and also here page 5 no.7. http://opensalts.us/References/SaltyComments/SC20.pdf
and last but not least U.S. Glass Company's catalogue, which George Duncan became part of.
At this point, I'm getting exhausted
The two identical pattern flint ones were just acquired very recently, as I thought they might help in the search.