And this I find generally in most Metalline colours, that though they consist of parts so exceedingly small, yet are they very deeply ting’d, they being so ponderous, and having such a multitude of terrestrial particles throng’d into a little room; so that ’tis difficult to find any particle transparent or resembling a pretious stone, though not impossible; for I have observ’d divers such shining and resplendent colours intermixt with the particles of Cinnaber, both natural and artificial, before it hath been ground and broken or flaw’d into Vermilion:  As I have also in Orpiment, Red-lead, and Bise, which makes me suppose, that those metalline colours are by grinding, not onely broken and separated actually into smaller pieces, but that they are also flaw’d and brused, whence they, for the most part, become opacous, like flaw’d Crystal or Glass, &c.  But for Smalts and verditures, I have been able with a Microscope to perceive their particles very many of them transparent.

Now, that the others also may be transparent, though they do not appear so to the Microscope, may be made probable by this Experiment:  that if you take ammel that is almost opacous, and grind it very well on a Porphyry, or Serpentine, the small particles will by reason of their flaws, appear perfectly opacous; and that ’tis the flaws that produce this opacousness, may be argued from this, that particles of the same Ammel much thicker if unflaw’d will appear somewhat transparent even to the eye; and from this also, that the most transparent and clear Crystal, if heated in the fire, and then suddenly quenched, so that it be all over flaw’d, will appear opacous and white.

And that the particles of Metalline colours are transparent, may be argued yet further from this, that the Crystals, or Vitriols of all Metals, are transparent, which since they consist of metalline as well as saline particles, those metalline ones must be transparent, which is yet further confirm’d from this, that they have for the most part, appropriate colours; so the vitriol of Gold is Yellow; of Copper, Blue, and sometimes Green; of Iron, green; of Tinn and Lead, a pale White; of Silver, a pale Blue, _&._

And next, the Solution of all Metals into menstruums are much the same with the Vitriols, or Crystals.  It seems therefore very probable, that those colours which are made by the precipitation of those particles out of the menstruums by transparent precipitating liquors should be transparent also.  Thus Gold precipitates with oyl of Tartar, or spirit of Urine into a brown Yellow, Copper with spirit of Urine into a Mucous blue, which retains its transparency.  A solution of sublimate (as the same Illustrious Authour I lately