To which I answer, that there is a great difference between diluting a colour and whitening of it; for diluting a colour, is to make the colour’d parts more thin, so that the ting’d light, which is made by trajecting those ting’d bodies, does not receive so deep a tincture; but whitening a colour is onely an intermixing of many clear reflections of light among the same ting’d parts; deepning also, and darkning or blacking a colour, are very different; for deepning a colour, is to make the light pass through a greater quantity of the same tinging body; and darkning or blacking a colour, is onely interposing a multitude of dark or black spots among the same ting’d parts, or placing the colour in a more faint light.

First therefore, as to the former of these operations, that is, diluting and deepning, most of the colours us’d by the Limners and Painters are incapable of, to wit, Vermilion and Red-lead, and Oker, because the ting’d parts are so exceeding small, that the most curious Grindstones we have, are not able to separate them into parts actually divided so small as the ting’d particles are; for looking on the most curiously ground Vermilion, and Oker, and Red-lead, I could perceive that even those small corpuscles of the bodies they left were compounded of many pieces, that is, they seem’d to be small pieces compounded of a multitude of lesser ting’d parts:  each piece seeming almost like a piece of Red Glass, or ting’d Crystal all flaw’d; so that unless the Grindstone could actually divide them into smaller pieces then those flaw’d particles were, which compounded that ting’d mote I could see with my Microscope, it would be impossible to dilute the colour by grinding, which, because the finest we have will not reach to do in Vermilion or Oker, therefore they cannot at all, or very hardly be diluted.

Other colours indeed, whose ting’d particles are such as may be made smaller, by grinding their colour, may be diluted.  Thus several of the Blues may be diluted, as Smalt and Bise; and Masticut, which is Yellow, may be made more faint:  And even Vermilion it self may, by too much grinding, be brought to the colour of Red-lead, which is but an Orange colour, which is confest by all to be very much upon the Yellow.  Now, though perhaps somewhat of this diluting of Vermilion by overmuch grinding may be attributed to the Grindstone, or muller, for that some of their parts may be worn off and mixt with the colour, yet there seems not very much, for I have done it on a Serpentine-stone with a muller made of a Pebble, and yet observ’d the same effect follow.

And secondly, as to the other of these operations on colours, that is, the deepning of them, Limners and Painters colours are for the most part also uncapable.  For they being for the most part opacous; and that opacousness, as I said before, proceeding from the particles, being very much flaw’d, unless we were able to joyn and re-unite those flaw’d particles again into one piece, we shall not be able to deepen the colour, which since we are unable to do with most of the colours which are by Painters accounted opacous, we are therefore unable to deepen them by adding more of the same kind.