20. Secondly, A Liquor may alter the Colour of a Body by freeing it from
those things that hindred it from appearing in its Genuine Colour; and
though this may be said to be rather a Restauration of a Body to its own
Colour, or a Retection of its native Colour, than a Change, yet still there
Intervenes in it a change of the Colour which the Body appear'd to be of
before this Operation. And such a change a Liquor may work, either by
Dissolving, or Corroding, or by some such way of carrying off that Matter,
which either Veil'd or Disguis'd the Colour that afterwards appears. Thus
we restore Old pieces of Dirty Gold to a clean and nitid Yellow, by putting
them into the Fire, and into _Aqua-fortis_, which take off the adventitious
Filth that made that pure Metall look of a Dirty Colour. And there is also
an easie way to restore Silver Coyns to their due Lustre, by fetching off
that which Discolour'd them. And I know a _Chymical_ Liquor, which I
employ'd to restore pieces of Cloath spotted with Grease to their proper
Colour, by Imbibing the Spotted part with this Liquor, which Incorporating
with the Grease, and yet being of a very Volatile Nature, does easily carry
it away with it Self. And I have sometimes try'd, that by Rubbing upon a
good Touch-stone a certain _Metalline_ mixture so Compounded, that the
Impression it left upon the Stone appear'd of a very differing Colour from
that of Gold, yet a little of _Aqua-fortis_ would in a Trice make the
Golden Colour disclose it self, by Dissolving the other _Metalline_
Corpuscles that conceal'd those of the Gold, which you know that
_Menstruum_ will leave Untouch'd.

21. Thirdly, A Liquor may alter the Colour of a Body by making a
Comminution of its Parts, and that principally two ways, the first by
Disjoyning and Dissipating those Clusters of Particles, if I may so call
them, which stuck more Loosely together, being fastned only by some more
easily Dissoluble Ciment, which seems to be the Case of some of the