But though upon a more attentive Consideration of this difference of
Colours, it seem'd probable to me, that divers (for I say not all) of those
Colours which we have just now call'd _Internal_, are rather produc'd by
the Coalition of Metalline Particles with those of the Salts, or other
Bodyes employ'd to work on them, than by the bare alteration of the parts
of the Metalls themselves: and though therefore we may call the obvious
Colours, Natural or Common, & the others Adventitious, yet because such
changes of Colours, from whatsoever cause they be resolv'd to proceed may
be properly enough taken in to illustrate our present Subject, we shall not
scruple to take notice of some of them, especially because there are among
them such as are produc'd without the intervention of Saline _Menstruums_.
Of the Adventitious Colours of Metalline Bodies the Chief sorts seem to be
these three. The first, such Colours as are produc'd without other
Additaments by the Action of the fire upon Metalls. The next such as emerge
from the Coalition of Metalline Particles with those of some _Menstruum_
imploy'd to Corrode a Metall or Precipitate it; And the last, The Colours
afforded by Metalline Bodyes either Colliquated with, or otherwise
Penetrating into, other Bodies, especially fusible ones. But these
(_Pyrophilus,_) are only as I told you, the _Chief_ sorts of the
adventitious Colours of Metalls, for there may others belong to them, of
which I shall hereafter have occasion to take notice of some, and of which
also there possibly may be others that I never took notice of.

And to begin with the first sort of Colours, 'tis well enough known to
Chymists, that Tin being Calcin'd by fire alone is wont to afford a White
_Calx_, and Lead Calcin'd by fire alone affords that most Common Red-Powder
we call _Minium:_ Copper also Calcin'd _per se_, by a long or violent fire,
is wont to yield (as far as I have had occasion to take notice of it) a
very Dark or Blackish Powder; That Iron likewise may by the Action of
Reverberated flames be turn'd into a Colour almost like that of Saffron,