I think it is time to remove the hard outer layer of encrustation and see if that aids
identification. I am not an expert on cleaning, so I disregarded all the well-intended advice about vinegar, baking soda, washing soda, Scotch and soda, and such. I did, however, use the tonic. Herewith the results after the first layer was removed.
Clearly, there was substantial hard deposits over an almost bubbly inner sheen.
New collectors should consult experts before attempting this method, or any other methods.
(Same water
bottle for
scale; unclear where G&T got to.)