Experiments and Considerations Touching Colours (1664)

by Robert Boyle

Wine, Spirit of Tartar freed from Acidity, or Chymical Oyl of Turpentine, (although Liquors which muſt be conceiv'd very Saline, if Chymiſts have, which is here no place to Diſpute, rightly aſcrib'd taſts to the Saline Principle of Bodyes,) have any Remarkable Power either to deprive our Tincture of its Cæruleous Colour, or reſtore it, when upon the Affuſion of Spirit of Vinegar it has diſappear'd.

EXPERIMENT XI.

And here I muſt not omit, Pyrophilus, to inform You, that we can ſhew You even in a Mineral Body ſomething that may ſeem very near of Kin to the Changeable Quality of the Tincture of Lignum Nephriticum, for we have ſeveral flat pieces of Glaſs, of the thickneſs of ordinary Panes for Windows one of which being interpoſed betwixt the Eye and a clear Light, appears of a Golden Colour, not much unlike that of the moderate Tincture of our Wood, but being ſo look'd upon as that the Beams of light are not ſo much Trajected thorough it as Reflected from it to the Eye, that Yellow ſeems to degenerate into a pale Blew, ſomewhat like that of a Turquoiſe. And what which may alſo appear ſtrange, is this,

that if in a certain poſture you hold one of theſe Plates Perpendicular to the Horizon, ſo that the Sun-beams ſhine upon half of it, the other half being Shaded, You may ſee that the part Shin'd upon will be of a much Diluter Yellow than the Shaded part which will appear much more Richly Colour'd; and if You alter the Poſture of the Glaſs, ſo that it be not held Perpendicular, but Parallel in reference to the Horizon, You may ſee, (which perhaps you will admire) the Shaded part look of a Golden Colour, but the other that the Sun ſhines freely on, will appear 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 Phænomena 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 me to obſerve to you, that there are but few Simple and Primary Colours (if I may ſo call them)

from whoſe Various Compoſitions all the reſt do as it were Reſult. For though Painters can imitate the Hues (though not always the Splendor) of thoſe almoſt Numberleſs differing Colours that are to be met with in the Works of Nature, and of Art, I have not yet found, that to exhibit this ſtrange Variety they need imploy any more than White, and Black, and Red, and Blew, and Yellow; theſe five, Variouſly Compounded, and (if I may ſo ſpeak) Decompounded, being ſufficient to exhibit a Variety and Number of Colours, ſuch, as thoſe that are altogether Strangers to the Painters Pallets, can hardly imagine.

Thus (for Inſtance) Black and White differingly mix'd, make a Vaſt company of Lighter and Darker Grays.