Experiments and considerations touching colours first occasionally written, among some other essays to a friend, and now suffer'd to come abroad as the beginning of an experimental history of colours / by the Honourable Robert Boyle ...

EXPERIMENT XLIX.

Meeting the other day, Pyrophilus, in an Italian book, that treats of other matters, with a way of preparing what the Au∣thor calls a Lacca of Vegetables, by which the Italians mean a kind of Extract fit for Painting, like that rich Lacca in English commonly call'd Lake, which is imploy'd by Painters as a glorious Red. And finding the Experiment not to be inconsiderable, and very defectively set down, it will not be amiss to acquaint you with what some Tryals have inform'd us, in reference to this

Experiment, which both by our Italian Author, and by divers of his Countrymen, is look'd upon as no trifling Secret.

Take then the root call'd in Latin Curcu∣ma, and in English Turmerick, (which I made use of, because it was then at hand, and is among Vegetables fit for that pur∣pose one of the most easiest to be had) and when it is beaten, put what Quantity of it you please into fair Water, adding to every pound of Water about a spoonfull or better of as strong a Lixivium or Solution of Pot-ashes as you can well make, clarifying it by Filtration before you put it to the Decoct∣ing water. Let these things boyl, or rather simper over a soft Fire in a clean glaz'd Earthen Vessel, till you find by the Immer∣sion of a sheet of White Paper (or by some other way of Tryal) that the Liquor is suf∣ficiently impregnated with the Golden Tincture of the Turmerick, then take the Decoction off the Fire, and Filter or Strain it that it may be clean, and leisurely drop∣ping into it a strong Solution of Roch Al∣lum, you shall find the Decoction as it were curdl'd, and the tincted part of it either to emerge, to subside, or to swim up and down, like little Yellow flakes; and if you pour this mixture into a Tunnel lin'd with Cap Paper, the Liquor that Filtred former∣ly

so Yellow, will now pass clean thorow the Filtre, leaving its tincted, and as it were curdled parts in the Filtre, upon which fair Water must be so often pour'd, till you have Dulcifi'd the matter therein contain'd, the sign of which Dulcification is (you know) when the Water that has pass'd through it, comes from it as tastless as it was pour'd on it. And if without Fil∣tration you would gather together the flakes of this Vegetable Lake, you must pour a great Quantity of fair Water upon the Decoction after the affusion of the Al∣luminous Solution, and you shall find the Liquor to grow clearer, and the Lake to settle together at the bottom, or emerge to the top of the Water, though some∣times having not pour'd out a sufficient Quantity of fair Water, we have observ'd the Lake partly to subside, and partly to emerge, leaving all the middle of the Liquor clear. But to make this Lake fit for use, it must by repeated affusions of fresh Water, be Dulcifi'd from the adhering Salts, as well as that separated by Filtration, and be spread and suffer'd to dry lei∣surely upon pieces of Cloth, with Brown Paper, or Chalk, or Bricks un∣der

them to imbibe the Moi∣sture .

Annotation I.

Whereas it is presum'd that the Magi∣stery of Vegetables obtain'd this way con∣sists but of the more. Soluble and Colour'd parts of the Plants that afford it, I must take the liberty to Question the Suppositi∣on. And for my so doing, I shall give you this account.

According to the Notions (such as they were) that I had concerning Salts; Allom, though to sense a Homogeneous Body, ought not to be reckon'd among true Salts, but to be it self look'd upon as a kind of Magistery, in regard that as Na∣tive Vitriol (for such I have had) con∣tains both a Saline substance and a Metall, whether Copper, or Iron, corroded by it, and associated with it; so Allom which may be of so near a kin to Vitriol, that in some places of England (as we are assur'd by good Authority the same stone will

sometimes afford both) seems manifestly to contain a peculiar kind of Acid Spirit, generated in the Bowels of the Earth, and some kind of stony matter dissolv'd by it. And though in making our ordinary Al∣lom, the Workmen use the Ashes of a Sea Weed (vulgarly call'd Kelp) and U∣rine: yet those that should know, inform us, that, here in England, there is besides the factitious Allom, Allom made by Na∣ture without the help of those Addita∣ments. Now (Pyrophilus) when I consi∣der'd this composition of Allom, and that Alcalizate Salts are wont to Praecipitate what acid Salts have dissolv'd, I could not but be prone to suspect that the Curdled Matter, which is call'd the Magistery of Ve∣getables, may have in it no inconsidera∣ble proportion of a stony substance Praeci∣pitated out of the Allom by the Lixivium, wherein the Vegetable had been decoct∣ed, and to shew you, that there is no ne∣cessity, that all the curdl'd substance must belong to the Vegetable, I shall add, that I took a strong Solution of Allom, and having Filtred it, by pouring in a conveni∣ent Quantity of a strong Solution of Pot-ashes, I presently, as I expected, turn'd the mixture into a kind of white Curds; which being put to Filtre, the Paper retain'd a sto∣ny

Calx, copious enough, very White, and which seem'd to be of a Mineral Nature, both by some other signes, and this, that little Bits of it being put upon a live Coal, which was Gently Blown whilst they were on it, they did neither melt nor fly away, and yon n ay keep a Quantity of this White substance for a good while, (nay for ought I can guess for a very long one) in a red hot Crucible without losing or spoiling it; nor did not Water wherein I purposely kept another parcel of such Calx, seem to do any more than wash away the looser adhering Salts from the stony Sub∣stance, which therefore seem'd unlikely to be separable by abiutions (though reitera∣ted) from the Praecipitated parts of the Ve∣getable, whose Lake is intended. And to shew you, that there is likewise in Allom a Body, with which the fix'd Salt of the Al∣calizare Solution will concoaguiare into a Saline Substance differing from either of them, I shall add, that I have taken plea∣sure to recover out of the slowly exhal'd Liquor, that pass'd through the filtre, and left the foremention'd Calx behind, a Body that at least seem'd a Salt very pretty to look on, as being very White, and consisting of an innumerable company of exceeding slender, and shining Particles, which

would in part easily melt at the flame of a Candle, and in part flye away with some little noise. But of this substance, and its odd Qualities more perhaps elsewhere; for now I shall only take notice to you, that I have likewise with Urinous Salts, such as the Spirit of Sal Armoniack, as well as with the Spirit of Urine it self, Nay, (if I much mistake not) ev'n with Stale Urine undi∣stil'd, easily Precipitated such a White Calx, as I was formerly speaking of, out of a Lim∣pid Solution of Allom, so that there is need of Circumspect on in judging of the Na∣tures of Liquors by Precipitations wherein Allom intervenes, else we may sometimes mistakingly imagine that to be Precipitated out of a Liquor by Allom, which is rather Precipitated out of Allom by the Liquor: And this puts me in mind to tell you, that 'tis not unpleasant to behold how quickly the Solution of Allom (or injected lumps of Allom) do's occasion the severing of the colour'd parts of the Decoction from the Liquor that seem'd to have so perfectly imbib'd them.

Annot. 11.

The above mention'd way of making Lakes we have tryed not only with Turme∣rick, but also with Madder, which yielded us a Red Lake; and with Rue, which affor∣ded us an extract, of (almost if not altoge∣ther) the same Colour with that of the leaves.

But in regard that 'tis Principally the Alcalizate Salt of the Pot-ashes, which en∣ables the water to Extract so powerfully the Tincture of the Decocted Vegetables, I fear that our Author may be mistaken by supposing that the Decoction will alwayes be of the very same Colour with the Ve∣getable it is made off. For Lixiviate Salts, to which Pot-ashes eminently belong, though by peircing and opening the Bodies of Vegetables, they prepare and dispose them to part readily with their Tincture, yet some Tinctures they do not only draw out, but likewise alter them, as may be ea∣sily made appear by many of the Experi∣ments already set down in this Treatise, and though Allom being of an Acid Na∣ture, its Solutions may in some Cases de∣stroy the Adventitious Colours produc'd by the Alcaly, and restore the former: yet

besides that Allom is not, as I have lately shown, a meer Acid Salt, but a mixt Body, and besides, that its operations are languid in comparison of the activity of Salts freed by Distillation, or by Incineration and Dissolution, from the most of their Earthy parts, we have seen already Examples, that in divers Cases an Acid Salt will not restore a Vegetable substance to the Colour of which an Alcalizate one had depriv'd it, but makes it assume a third very differing from both, as we formerly told you, that if Syrrup of Violets were by an Alcaly turn'd Green, (which Colour, as I have try'd, may be the same way produc'd in the Violet∣leaves themselves without any Relation to a Syrrup) an Acid Salt would not make it Blew again, but Red. And though I have by this way of making Lakes, made Magi∣steries (for such they seem to be) of Brazil, and as I remember of Cochinele it self, and of other things, Red, Yellow or Green which Lakes were enobled with a Rich Colour, and others had no bad one; yet in some the colour of the Lake seem'd rather inferiour than otherwise to that of the Plant, and in others it seem'd both very differing, and much worse; but Writing this in a time and place where I cannot provide my self of Flowres and other Vegetables to pro∣secute

such Tryals in a competent variety of Subjects, I am content not to be positive in delivering a judgment of this way of Lakes, till Experience, or You, Pyrophilus, shall have afforded me a fuller and more particular Information.

Annotation III.

And on this occasion (Pyrophilus) I must here (having forgot to do it sooner) ad∣vertise you once for all, that having written several of the foregoing Experiments, not only in haste but at seasons of the year, and in places wherein I could not furnish my self with such Instruments, and such a vari∣ety of Materials, as the design of giving you an Introduction into the History of Colours requir'd, it can scarce be otherwise but that divers of the Experiments, that I have set down, may afford you some matter of new Tryals, if you think fit to supply the defi∣ciencies of some of them (especially the freshly mention'd about Lakes, and those that concern Emphatical Colours) which deficiencies for want of being befriended with accommodations I could better dis∣cern than avoid.

Annotation IV.

The use of Allom is very great as well as familiar in the Dyers Trade, and I have not been ill pleas'd with the use I have been able to make of it in preparing other pigments than those they imploy with Ve∣getable Juices. But the Lucriferous pra∣ctises of Dyers and other Tradesmen, I do, for Reasons that you may know when you please, purposely forbear in this Essay, though not strictly from pointing at, yet from making it a part of my present work explicitly and circumstantially to deliver, especially since I now find (though late and not without some Blushes at my prolixi∣ty) that what I intended but for a short Essay, is already swell'd into almost a Vo∣lume.

Notes

• The Curious Reader that desires fur∣ther Information concerning Lakes, may Resort to the 7th Book of Neri's Art of Glass, Englished (6 or 7 years since the Writing of this 49th Experiment) and Illustrated with Learned Observations, by the Inquisitive and Experienc'd Dr. Charles Merret.