We have often taken notice, as of a remarkable thing, that Metalls as they appear to the Eye, before they come to be farther alter’d by other Bodyes, do exhibit Colours very different from those which the Fire and the Menstruum, either apart, or both together, do produce in them; especially considering that these Metalline Bodyes are after all these disguises reducible not only to their former Metalline Consistence and other more radical properties, but to their Colour too, as if Nature had given divers Metalls to each of them a double Colour, an External, and an Internal; 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, may be easily deduc’d from the Preparation of that Powder, which by reason of its Colour and of the Metall ’tis made of is by Chymists call’d, Crocus Martis per se.  And that Mercury made by the stress of Fire, may be turn’d into a Red Powder, which Chymists call Precipitate per se, I elsewhere more particularly declare.