Excerpts from Robert Boyle, 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 (London: Printed for Henry Herringman, 1664).
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|derthem to imbibe the Moi|sture .
. . . .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|secutesuch 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.
EXPERIMENT XX.
Take good Syrrup of Violets, Impraeg|nated with the Tincture of the flowers, drop a little of it upon a White Paper (for by that means the Change of Colour will be more conspicuous, and the Experiment may be practis’d in smaller Quantities) and on this Liquor let fall two or three drops of Spirit either of Salt or Vinegar, or almost any other eminently Acid Liquor, and upon the Mixture of these you shall find the Syrrup immediatly turn’d Red, and the way of Effecting such a Change has not been unknown to divers Personswho have produc’d the like, by Spirit of Vitriol, or juice of Limmons, but have Groundlessly ascrib’d the Effect to some Peculiar Quality of those two Liquors, whereas, (as we have already intimated) almost any Acid Salt will turn Syrrup of Violets Red. But to improve the Experi|ment, let me add what has not (that I know of) been hitherto observ’d, and has, when we first shew’d it them, appear’d something strange, even to those that have been inquisitive into the Nature of Colours; namely, that if instead of Spirit of Salt, or that of Vinegar, you drop upon the Syrrup of Violets a little Oyl of Tartar per Deliquium, or the like quantity of Solu|tion of Potashes, and rubb them together with your finger, you shall find the Blew Colour of the Syrrup turn’d in a moment into a perfect Green, and the like may be perform’d by divers other Liquors, as we may have occasion elsewhere to Inform you.
. . . . EXPERIMENT XXI.
There is a Weed, more known to Plow|men than belov’d by them, whose Flowers from their Colour are com|monly call’d Blew-bottles, and Corn-weed from their Growing among Corn. These Flowers some Ladies do, upon the ac|count of their Lovely Colour, think worth the being Candied, which when they are, they will long retain so fair a Colour, as makes them a very fine Sallad in the Win|ter. But I have try’d, that when they are freshly gather’d, they will afford a Juice, which when newly express’d, (for in some cases ’twill soon enough degenerate) affords a very deep and pleasant Blew. Now, (to draw this to our present Scope) by dropping on this fresh Juice, a little Spirit of Salt, (that being the Acid Spirit I had then at hand) it immediately turn’d (as I predicted) into a Red. And if in|stead of the Sowr Spirit I mingled with it a little strong Solution of an Alcalizate Salt, it did presently disclose a lovely Green; the same Changes being by those differing sorts of Saline Liquors, producible in this Natural juice, that we lately mention’d tohave happen’d to that factitious Mixture, the Syrrup of Violets. And I remember, that finding this Blew Liquor, when freshly made, to be capable of serving in a Pen for an Ink of that Colour, I attempted by moistning one part of a piece of White Paper with the Spirit of Salt I have been mentioning, and another with some Al|calizate or Volatile Liquor, to draw a Line on the leisurely dry’d Paper, that should, e’vn before the Ink was dry, ap|pear partly Blew, partly Red, and partly Green: But though the latter part of the Experiment succeeded not well, (whether because Volatile Salts are too Fugitive to be retain’d in the Paper, and Alcalizate ones are too Unctuous, or so apt to draw Moisture from the Air, that they keep the Paper from drying well) yet the former Part succeeded well enough; the Blew and Red being Conspicuous enough to afford a surprizing Spectacle to those, I acquaint not with (what I willingly allow you to call) the Trick.
. . . .
Experiment XXV
For Ripe Privet Berries (for instance) being crush’d upon White Paper, though they stain it with a Purplish Colour, yet if we let fall on some part of it two or three drops of Spirit of Salt, and on the other part a little more of the strong Solution of Pot-ashes, the former Liquor immediately turn’d that part of the Thick Juice or Pulp, on which it fell, into a lovely Red, and the latter turn’d the other part of it into a delightfull Green. Though I will not undertake, that those Colours in that Substance shall not be much more. Orient, than Lasting; and though (Pyrophilus) this Experiment may seem to be almost the same with those al|ready deliver’d concerning Syrrup of Vio|lets, and the Juice of Blew-bottles, yet I think it not amiss to take this Occasion to inform you, that this Experiment reaches much farther, than perhaps you yet ima|gine, and may be of good Use to those, whom it concerns to know, how Dying Stuffs may be wrought upon by Saline Li|quors. For, I have found this Experiment to succeed in so many Various Berries, Flowers, Blossoms, and other finer Parts of Vegetables, that neither my Memory, nor my Leisure serves me to enumerate them. And it is somewhat surprizing to see, by how Differingly-colour’d Flowers, or Blossoms, (for example) the Paper beingstain’d, will by an Acid Spirit be imme|diately turn’d Red, and by any Alcaly or any Urinous Spirit turn’d Green; inso|much that ev’n the crush’d Blossoms of Meserion, (which I gather’d in Winter and frosty Weather) and those of Pease, crush’d upon White Paper, how remote soever their Colours be from Green, would in a moment pass into a deep Degree of that Colour, upon the Touch of an Alca|lizate Liquor. To which let us add, That either of those new Pigments (if I may so call them) may by the Affusion of enough of a contrary Liquor, be presently chang’d from Red into Green, and from Green into Red, which Observation will hold also in Syrrup of Violets; Juices of Blew-bottles, &c.
.. . EXPERIMENT XXVI.
And, (first) I thought fit to try the Operation of Acid Salts upon Vegetable Substances, that are already and by their own Nature Red. And accordingly I made Trial upon Syrrup of Clove-july-flowers, the clear express’d Juice of the succulent Berries of Spina Cervina, or Buck-thorn (which I had long kept by me for the sake of its deep Colour) upon Red Roses, Infusion of Brazil, and divers other Vegetable Substances, on some of which crush’d (as is often mention’d) upon White Paper, (which is also to be under|stood in most of these Experiments, if no Circumstance of them argue otherwise) Spirit of Salt either made no considerable Change, or alter’d the Colour but from a Darker to a Lighter Red. How it will succeed in many other Vegetable Juices, and Infusions of the same Colour, I have at present so few at hand, that I must leave you to find it our your self. But as for the Operation of the other sorts of Salts upon these Red Substances, I found it not very Uniform, some Red, or Reddish Infusions, as of Roses, being turn’d thereby into a dirty Colour, but yet inclining to Green. Nor was the Syrrup of Clove-july-flowers turn’d by the Solution of Pot-ashes to a much better, though somewhat a Greener, Colour. Another sort of Red Infusions was by an Alcaly not turn’d into a Green, but advanc’d into a Crimson, as I shall have occasion to note ere long. But there were other sorts, as particularly the lovely Colour’d juice of Buckthorn Berries, that readily pass’d into a lovely Green.
EXPERIMENT XXVII.
Among other Vegetables, which we thought likely to afford Exceptions to the General Observation about the differing Changes of Colours produc’d by Acid and Sulphureous Salts, we thought fit to make Trial upon the Flowers of Jasmin,they being both White as to Colour, and esteem’d to be of a more Oyly nature than other Flowers. Whereupon having taken the White parts only of the Flowers, and rubb’d them somewhat hard with my Fin|ger upon a piece of clean Paper, it appear’d very little Discolour’d. Nor had Spirit of Salt, wherewith I moisten’d one part of it, any considerable Operation upon it. But Spirit of Urine, and somewhat more effe|ctually a strong Alcalizate Solution, did immediately turn the almost Colourless Paper moisten’d by the Juice of the Jasmin, not as those Liquors are wont to do, when put upon the Juices of other Flowers, of a good Green, but of a Deep, though some|what Greenish Yellow, which Experiment I did afterwards at several times repeat with the like success. But it seems not that a great degree of Unctuousness is necessary to the Production of the like Effects, for when we try’d the Experiment with the Leaves of those purely White Flowers that appear about the end of Winter, and are commonly call’d Snow drops, the event, was not much unlike that, which, we have been newly mentioning.
EXPERIMENT XXVIII.
Another sort of Instances to show, how much changes of Colours effected by Salts, depend upon the particular Texture of the Colour’d Bodies, has been afforded me by several Yellow Flowers, and other Vege|tables, as Mary-gold Leaves, early Prim-roses, fresh Madder, &c. For being rubb’d upon White Paper, till they im|bued it with their Colour, I found not, that by the addition of Alcalizate Liquors, nor yet by that of an Urinous Spirit, they would be turn’d either Green or Red: nor did so Acid a Spirit, as that of Salt, consi|derably alter their Colour, save that it seem’d a little to Dilute it. Only in some early Prim-roses it destroy’d the greatest part of the Colour, and made the Paper almost White agen. And Madder also afforded some thing peculiar, and very differing from what we have newly men|tion’d: For having gather’d some Roots of it, and, (whilst they were recent) ex|press’d upon White Paper the Yellow Juice, an Alcalizate Solution drop’d upon it did not turn it either Green or White, but Red. And the bruis’d Madder it self being drench’d with the like Alcalizate Solution, exchang’d also its Yellowishness for a Redness.
An admonition touching the four preceding Experiments.
Having thus (Pyrophilus) given you divers Instances, to countenance the Gene|ral observation deliver’d in the twenty fifth Experiment, and divers Exceptions where|by it ought to be Limited; I must leave the further Inquiry into these Matters to your own Industry. For not remembring at present many of those other Trials, long since made to satisfie my self about Parti|culars, and not having now the Oppor|tunity to repeat them, I must content my Self to have given you the Hint, and the ways of prosecuting the search your Self; and only declare to you in general, that, As I have made many Trials, unmention’d in this Treatise, whose Events were agree|able to those mention’d in the twenty fifth Experiment, so (to name now no other Instances) what I have try’d with Acid and Sulphureous Salts upon the Pulp of Juniper Berries, rubb’d upon White Pa|per, inclines me to think, That among that vast Multitude, and strange Variety of Plants that adorn the face of the Earth, perhaps many other Vegetables may be found, on which such Menstruums may nothave such Operations, as upon the Juice of Violets, Pease-blossoms, &c. no nor upon any of those three other sorts of Vegeta|bles, that I have taken notice of in the three fore-going Experiments. It sufficiently ap|pearing ev’n by these, that the effects of a Salt upon the Juices of particular Vege|tables do very much depend upon their particular Textures.