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 mention’d shews in his 40. Experiment) _precipitates_ with oyl of _Tartar_ _per deliquium_, into an Orange colour’d _precipitate_; nor is it less probable, that the _calcination_ of those _Vitriols_ by the fire, should have their particles transparent: Thus _Saccarum Saturni_, or the _Vitriol of Lead_ by _calcination_ becomes a deep Orange-colour’d _minium_, which is a kind of _precipitation_ by some Salt which proceeds from the fire; common _Vitriol_ _calcin’d_, yields a deep Brown Red, &c. A third Argument, that the particles of Metals are transparent, is, that being _calcin’d_, and melted with Glass, they tinge the Glass with transparent colours. Thus the _Calx_ of Silver tinges the Glass on which it is anneal’d with a lovely Yellow, or Gold colour, &c.