When wandering out and about in the field sometime back in April, when the air still had quite a chill, and the snow had not completely gone, I came upon some bits and pieces of history: a few remains from fire assaying. This was a small site, not necessarily the location of an actual assay lab, maybe just a place where someone had dumped some miscellaneous debris.
Here's the biggest, most distinctive chunk I found: part of the bottom of a fire assay crucible, a crucible used in fire assay for gold and silver.
The inside has a thin coating of what was once fused ore and flux, now cooled to a greenish glass.
I think the bottom of the crucible holds a vague clue to the manufacturer of the crucible, and hence to its age, but not one I know how to decipher.
Fire assay / cupellation at Wikipedia - a fairly abbreviated description of the fire assay process.
What is Fire Assaying? - a more complete description.
A Textbook of fire assaying - by Edward Everett Bugbee, the classic and complete text on fire assaying. I used a 1933 edition of Bugbee when doing fire assays for my thesis.