till I have opportunity to make farther Tryal, I cannot but suspect, either
that Silver which is not (which is not very probable) brought to a perfect
Fusion and Colliquation with Glass, may impart to it other Colours than
when Neal'd upon it, or else (which is less unlikely) that though Silver
Beaters usually chuse the finest Coyn they can get, as that which is most
extensive under the Hammer, yet the Silver-leaves of which this Shel-silver
was made, might retain so much Copper as to enable it to give the
predominant tincture to the Glass.

For, I must proceed to tell you (_Pyrophilus_) as another instance of the
Adventitious Colours of Metals, that which is something strange, Namely,
That though Copper Calcin'd _per se_ affords but a Dark and basely Colour'd
_Calx_, yet the Glassmen do with it, as themselves inform me, Tinge their
Glass green. And I remember, that when once we took some crude Copper, and
by frequent Ignition quenching it in Water had reduc'd it to a Dark and
Ill-colour'd Powder, and afterward kept it in Fusion in about a 100. times
its weight of fine Glass, we had, though not a Green, yet a Blew colour'd
Mass, which would perhaps have been Green, if we had hit right upon the
Proportion of the Materials, and the Degree of Fire, and the Time wherein
it ought to be kept in Fusion, so plentifully does that Metal abound in a
Venerial Tincture, as Artists call it, and in so many wayes does it
disclose that Richness. But though Copper do as we have said give somewhat
near the like Colour to Glass, which it does to _Aqua-fortis_, yet it seems
worth inquiry, whether those new Colours which Mineral Bodies disclose in
melted Glass, proceed from the Coalition of the Corpuscles of the Mineral
with the Particles of the Glass as such, or from the Action (excited or
actuated by fire) of the Alcalizate Salt (which is a main Ingredient of
Glass,) upon the Mineral Body, or from the concurrence of both these
Causes, or else from any other. But to return to that which we were saying,
we may observe that _Putty_ made by calcining together a proportion of Tin