considerably Blew, and as you remove any part of the Glass thus held Horizontally into the Sun-beams or Shade, it will in the twinkling of an Eye seem to pass from one of the above mention’d Colours to the other, the Sun-beams Trajected through it upon a sheet of White Paper held near it, do colour it with a Yellow, somewhat bordering upon a Red, but yet the Glass may be so oppos’d to the Sun, that it may upon Paper project a mix’d Colour here and there more inclin’d to Yellow, and here and there more to Blew.  The other Phaenomena of this odd Glass, I fear it would be scarce worth while to Record, and therefore I shall rather advertise You, First that in the trying of these Experiments with it, you must take notice that one of the sides has either alone, or at least principally its Superficial parts dispos’d to the Reflection of the Blew Colour above nam’d, and that therefore you must have a care to keep that side nearest to the Eye.  And next, that we have our selves made Glasses not unfit to exhibit an Experiment not unlike that I have been speaking of, by laying upon pieces of Glass some very finely foliated Silver, and giving it by degrees a much stronger Fire than is requisite or usual for the Tinging of Glasses of other Colours.  And this Experiment, not to mention that it was made without a Furnace in which Artificers that Paint Glass are wont to be very Curious, is the more considerable, because, that though a Skilfull Painter could not deny to me that ’twas with Silver he Colour’d his Glasses Yellow; yet he told me, that when to Burn them (as they speak) he layes on the plates of Glass nothing but a Calx of Silver Calcin’d without Corrosive Liquors, and Temper’d with Fair Water, the Plates are Ting’d of a fine Yellow that looks of a Golden Colour, which part soever of it you turn to or from the Light; whereas (whether it be what an Artificer would call Over-doing, or Burning, or else the imploying the Silver Crude that makes the Difference,) we have found more than once, that some Pieces of Glass prepar’d as we have related, though held against the Light they appear’d of a Transparent Yellow, yet look’d on with ones back turn’d to the Light they exhibited an Untransparent Blew.

EXPERIMENT XII.

If you will allow me, Pyrophilus, for the avoiding of Ambiguity, to imploy the Word Pigments, to signifie such prepared materials (as Cochinele, Vermilion, Orpiment,) as Painters, Dyers and other Artificers make use of to impart or imitate particular Colours, I shall be the better understood in divers passages of the following papers, and particularly when I tell you, That the mixing of Pigments being no inconsiderable part of the Painters Art, it may seem an Incroachment in me to meddle with it.  But I think I may easily be excus’d (though I do not altogether pass it by) if I restrain my self to the making of a Transient mention of some few of their Practices about this matter; and that only so far forth, as may warrant