Micrographia, by Robert Hooke

Observ. x. Of Metalline, and other real Colours.

Having in the former Discourse, from the Fundamental cause of Colour, made it probable, that there are but two Colours, and shewn, that the Phantasm of Colour is caus'd by the sensation of the oblique or uneven pulse of Light which is capable of no more varieties than two that arise from the two sides of the oblique pulse, though each of those be capable of infinite gradations or degrees (each of them beginning from White, and ending the one in the deepest Scarlet or Yellow, the other in the deepest Blue) I shall in this Section set down some Observations which I have made of other colours, such as Metalline powders tinging or colour'd bodies and several kinds of tinctures or ting'd liquors, all which, together with those I treated of in the former Observation will, I suppose, comprise the several subjects in which colour is observ'd to be inherent, and the several manners by which it inheres, or is apparent in them. And here I shall endeavour to shew by what composition all kind of compound colours are made, and how there is no colour in the world but may be made from the various degrees of these two colours, together with the intermixtures of Black and White.

And this being so, as I shall anon shew, it seems an evident argument to me, that all colours whatsoever, whether in fluid or solid, whether in very transparent or seemingly opacous, have the same efficient cause, to wit, some kind of refraction whereby the Rays that proceed from such bodies, have their pulse obliquated or confus'd in the manner I explicated in the former Section; that is, a Red is caus'd by a duplicated or confus'd pulse, whose strongest pulse precedes, and a weaker follows: and a Blue is caus'd by a confus'd pulse, where the weaker pulse precedes, and the stronger follows. And according as these are, more or less, or variously mixt and compounded, so are the sensations, and consequently the phantasms of colours diversified.

To proceed therefore; I suppose, that all transparent colour'd bodies, whether fluid or solid, do consist at least of two parts, or two kinds of substances, the one of a substance of a somewhat differing refraction from the other. That one of these substances which may be call'd the tinging substance, does consist of distinct parts, or particles of a determinate bigness which are disseminated, or dispers'd all over the other: That these particles, if the body be equally and uniformly colour'd, are evenly rang'd and dispers'd over the other contiguous body; That where the body is deepest ting'd, there these particles are rang'd thickest, and where 'tis but faintly ting'd, they are rang'd much thinner, but uniformly. That by the mixture of another body that unites with either of these, which has a differing refraction from either of the other, quite differing effects will be produc'd, that is, the consecutions of the confus'd pulses will be much of another kind, and consequently produce other sensations and phantasms of colours, and from a Red may turn to a Blue, or from a Blue to a Red, &c.

Now, that this may be the better understood, I shall endeavour to Schem. 6.
Fig. 7.
explain my meaning a little more sensible by a Scheme: Suppose we therefore in the seventh Figure of the sixth Scheme, that ABCD represents a Vessel holding a ting'd liquor, let IIIII, &c. be the clear liquor, and let the tinging body that is mixt with it be EE, &c. FF, &c. GG, &c. HH, &c. whose particles (whether round, or some other determinate Figure is little to our purpose) are first of a determinate and equal bulk. Next, they are rang'd into the form of Quincunx, or Equilaterotriangular order, which that probably they are so, and why they are so, I shall elsewhere endeavour to shew. Thirdly, they are of such a nature, as does either more easily or more difficultly transmit the Rays of light then the liquor; if more easily, a Blue is generated, and if more difficultly, a Red or Scarlet.

And first, let us suppose the tinging particles to be of a substance that does more impede the Rays of light, we shall find that the pulse or wave of light mov'd from AD to BC, will proceed on, through the containing medium by the pulses or waves KK, LL, MM, NN, OO; but because several of these Rays that go to the constitution of these pulses will be slugged or stopped by the tinging particles E, F, G, H; therefore there shall be secundary and weak pulse that shall follow the Ray, namely PP which will be the weaker: first, because it has suffer'd many refractions in the impeding body; next, for that the Rays will be a little dispers'd or confus'd by reason of the refraction in each of the particles, whether round or angular; and this will be more evident, if we a little more closely examine any one particular tinging Globule.

Schem. 6.
Fig. 8.
Suppose we therefore AB in the eighth Figure of the sixth Scheme, to represent a tinging Globule or particle which has a greater refraction than the liquor in which it is contain'd: Let CD be a part of the pulse of light which is propagated through the containing medium; this pulse will be a little stopt or impeded by the Globule, and so by that time the pulse is past to EF that part of it which has been impeded by passing through the Globule, will get but to LM, and so that pulse which has been propagated through the Globule, to wit, LM, NO, PQ, will always come behind the pulses EF, GH, IK, &c.

Next, by reason of the greater impediment in AB, and its Globular Figure, the Rays that pass through it will be dispers'd, and very much scatter'd. Whence CA and DB which before went direct and parallel, will after the refraction in AB, diverge and spread by AP, and BQ; so that as the Rays do meet with more and more of these tinging particles in their way, by so much the more will the pulse of light further lagg behind the clearer pulse, or that which has fewer refractions, and thence the deeper will the colour be, and the fainter the light that is trajected through it; for not onely many Rays are reflected from the surfaces of AB, but those Rays that get through it are very much disordered.

By this Hypothesis there is no one experiment of colour that I have yet met with, but may be, I conceive, very rationably solv'd, and perhaps, had I time to examine several particulars requisite to the demonstration of it, I might prove it more than probable, for all the experiments about the changes and mixings of colours related in the Treatise of Colours, published by the Incomparable Mr. Boyle, and multitudes of others which I have observ'd, do so easily and naturally flow from those principles, that I am very apt to think it probable, that they own their production to no other secundary cause: As to instance in two or three experiments. In the twentieth Experiment, this Noble Authour has shewn that the deep bluish purple-colour of Violets, may be turn'd into a Green, by Alcalizate Salts, and to a Red by acid; that is, a Purple consists of two colours, a deep Red, and a deep Blue; when the Blue is diluted, or altered, or destroy'd by acid Salts, the Red becomes predominant, but when the Red is diluted by Alcalizate, and the Blue heightned, there is generated a Green; for of a Red diluted, is made a Yellow, and Yellow and Blue make a Green.

Now, because the spurious pulses which cause a Red and a Blue, do the one follow the clear pulse, and the other precede it, it usually follows, that those Saline refracting bodies which do dilute the colour of the one, do deepen that of the other. And this will be made manifest by almost all kinds of Purples, and many sorts of Greens, both these colours consisting of mixt colours; for if we suppose A and A in the ninth Figure, to represent two pulses of clear light, which follow each other at a convenient distance, AA, each of which has a spurious pulse preceding it, as BB, which makes a Blue, and another following it, as CC, which makes a Red, the one caus'd by tinging particles that have a greater refraction, the other by others that have a less refracting quality then the liquor or Menstruum in which these are dissolv'd, whatsoever liquor does so alter the refraction of the one, without altering that of the other part of the ting'd liquor, must needs very much alter the colour of the liquor; for if the refraction of the dissolvent be increas'd, and the refraction of the tinging particles not altered, then will the preceding spurious pulse be shortned or stopt, and not out-run the clear pulse so much; so that BB will become EE, and the Blue be diluted, whereas the other spurious pulse which follows will be made to lagg much more, and be further behind AA than before, and CC will become ff, and so the Yellow or Red will be heightned.

A Saline liquor therefore, mixt with another ting'd liquor, may alter the colour of it several ways, either by altering the refraction of the liquor in which the colour swims: or secondly by varying the refraction of the coloured particles, by uniting more intimately either with some particular corpuscles of the tinging body, or with all of them, according as it has a congruity to some more especially, or to all alike: or thirdly, by uniting and interweaving it self with some other body that is already joyn'd with the tinging particles, with which substance it may have a congruity, though it have very little with the particles themselves: or fourthly, it may alter the colour of a ting'd liquor by dis-joyning certain particles which were before united with the tinging particles, which though they were somewhat congruous to these particles, have yet a greater congruity with the newly infus'd Saline menstruum. It may likewise alter the colour by further dissolving the tinging substance into smaller and smaller particles, and so diluting the colour; or by uniting several particles together as in precipitations, and so deepning it, and some such other ways, which many experiments and comparisons of differing trials together, might easily inform one of.

From these Principles applied, may be made out all the varieties of colours observable, either in liquors, or any other ting'd bodies, with great ease, and I hope intelligible enough, there being nothing in the notion of colour, or in the suppos'd production, but is very conceivable, and may be possible.

The greatest difficulty that I find against this Hypothesis, is, that there seem to be more distinct colours then two, that is, then Yellow and Blue. This Objection is grounded on this reason, that there are several Reds, which diluted, make not a Saffron or pale Yellow, and therefore Red, or Scarlet seems to be a third colour distinct from a deep degree of Yellow.

To which I answer, that Saffron affords us a deep Scarlet tincture, which may be diluted into as pale a Yellow as any, either by making a weak solution of the Saffron, by infusing a small parcel of it into a great quantity of liquor, as in spirit of Wine, or else by looking through a very thin quantity of the tincture, and which may be heightn'd into the loveliest Scarlet, by looking through a very thick body of this tincture, or through a thinner parcel of it, which is highly impregnated with the tinging body, by having had a greater quantity of the Saffron dissolv'd in a smaller parcel of the liquor.

Now, though there may be some particles of other tinging bodies that give a lovely Scarlet also, which though diluted never so much with liquor, or looked on through never so thin a parcel of ting'd liquor, will not yet afford a pale Yellow, but onely a kind of faint Red; yet this is no argument but that those ting'd particles may have in them the faintest degree of Yellow, though we may be unable to make them exhibit it; For that power of being diluted depending upon the divisibility of the ting'd body, if I am unable to make the tinging particles so thin as to exhibit that colour, it does not therefore follow, that the thing is impossible to be done; now, the tinging particles of some bodies are of such a nature, that unless there be found some way of comminuting them into less bulks then the liquor does dissolve them into, all the Rays that pass through them must necessarily receive a tincture so deep, as their appropriate refractions and bulks compar'd with the proprieties of the dissolving liquor must necessarily dispose them to empress, which may perhaps be a pretty deep Yellow, or pale Red.

And that this is not gratis dictum, I shall add one instance of this kind, wherein the thing is most manifest.

If you take Blue Smalt, you shall find, that to afford the deepest Blue, which cæteris paribus has the greatest particles or sands; and if you further divide, or grind those particles on a Grindstone, or porphyry stone, you may by comminuting the sands of it, dilute the Blue into as pale a one as you please, which you cannot do by laying the colour thin; for wheresoever any single particle is, it exhibits as deep a Blue as the whole mass. Now, there are other Blues, which though never so much ground, will not be diluted by grinding, because consisting of very small particles, very deeply ting'd, they cannot by grinding be actually separated into smaller particles then the operation of the fire, or some other dissolving menstruum, reduc'd them to already.

Thus all kind of Metalline colours, whether precipitated, sublim'd, calcin'd, or otherwise prepar'd, are hardly chang'd by grinding, as ultra marine is not more diluted; nor is Vermilion or Red-lead made of a more faint colour by grinding; for the smallest particles of these which I have view'd with my greatest Magnifying-Glass, if they be well enlightned, appear very deeply ting'd with their peculiar colours; nor, though I have magnified and enlightned the particles exceedingly, could I in many of them, perceive them to be transparent, or to be whole particles, but the smallest specks that I could find among well ground Vermilion and Red-lead, seem'd to be a Red mass, compounded of a multitude of less and less motes, which sticking together, compos'd a bulk, not one thousand thousandth part of the smallest visible sand or mote.

And this I find generally in most Metalline colours, that though they consist of parts so exceedingly small, yet are they very deeply ting'd, they being so ponderous, and having such a multitude of terrestrial particles throng'd into a little room; so that 'tis difficult to find any particle transparent or resembling a pretious stone, though not impossible; for I have observ'd divers such shining and resplendent colours intermixt with the particles of Cinnaber, both natural and artificial, before it hath been ground and broken or flaw'd into Vermilion: As I have also in Orpiment, Red-lead, and Bise, which makes me suppose, that those metalline colours are by grinding, not onely broken and separated actually into smaller pieces, but that they are also flaw'd and brused, whence they, for the most part, become opacous, like flaw'd Crystal or Glass, &c. But for Smalts and verditures, I have been able with a Microscope to perceive their particles very many of them transparent.

Now, that the others also may be transparent, though they do not appear so to the Microscope, may be made probable by this Experiment: that if you take ammel that is almost opacous, and grind it very well on a Porphyry, or Serpentine, the small particles will by reason of their flaws, appear perfectly opacous; and that 'tis the flaws that produce this opacousness, may be argued from this, that particles of the same Ammel much thicker if unflaw'd will appear somewhat transparent even to the eye; and from this also, that the most transparent and clear Crystal, if heated in the fire, and then suddenly quenched, so that it be all over flaw'd, will appear opacous and white.

And that the particles of Metalline colours are transparent, may be argued yet further from this, that the Crystals, or Vitriols of all Metals, are transparent, which since they consist of metalline as well as saline particles, those metalline ones must be transparent, which is yet further confirm'd from this, that they have for the most part, appropriate colours; so the vitriol of Gold is Yellow; of Copper, Blue, and sometimes Green; of Iron, green; of Tinn and Lead, a pale White; of Silver, a pale Blue, &.

And next, the Solution of all Metals into menstruums are much the same with the Vitriols, or Crystals. It seems therefore very probable, that those colours which are made by the precipitation of those particles out of the menstruums by transparent precipitating liquors should be transparent also. Thus Gold precipitates with oyl of Tartar, or spirit of Urine into a brown Yellow, Copper with spirit of Urine into a Mucous blue, which retains its transparency. A solution of sublimate (as the same Illustrious Authour I lately mention'd shews in his 40. Experiment) precipitates with oyl of Tartar per deliquium, into an Orange colour'd precipitate; nor is it less probable, that the calcination of those Vitriols by the fire, should have their particles transparent: Thus Saccarum Saturni, or the Vitriol of Lead by calcination becomes a deep Orange-colour'd minium, which is a kind of precipitation by some Salt which proceeds from the fire; common Vitriol calcin'd, yields a deep Brown Red, etc.

A third Argument, that the particles of Metals are transparent, is, that being calcin'd, and melted with Glass, they tinge the Glass with transparent colours. Thus the Calx of Silver tinges the Glass on which it is anneal'd with a lovely Yellow, or Gold colour, &c.

And that the parts of Metals are transparent, may be farther argued from the transparency of Leaf-gold, which held against the light, both to the naked eye, and the Microscope, exhibits a deep Green. And though I have never seen the other Metals laminated so thin, that I was able to perceive them transparent, yet, for Copper and Brass, if we had the same conveniency for laminating them, as we have for Gold, we might, perhaps, through such plates or leaves, find very differing degrees of Blue, or Green; for it seems very probable, that those Rays that rebound from them ting'd, with a deep Yellow, or pale Red, as from Copper, or with a pale Yellow, as from Brass, have past through them; for I cannot conceive how by reflection alone those Rays can receive a tincture, taking any Hypothesis extant.

So that we see there may a sufficient reason be drawn from these instances, why those colours which we are unable to dilute to the palest Yellow, or Blue, or Green, are not therefore to be concluded not to be a deeper degree of them; for supposing we had a great company of small Globular essence Bottles, or round Glass bubbles, about the bigness of a Walnut, fill'd each of them with a very deep mixture of Saffron, and that every one of them did appear of a deep Scarlet colour, and all of them together did exhibit at a distance, a deep dy'd Scarlet body. It does not follow, because after we have come nearer to this congeries, or mass, and divided it into its parts, and examining each of its parts severally or apart, we find them to have much the same colour with the whole mats; it does not, I say, therefore follow, that if we could break those Globules smaller, or any other ways come to see a smaller or thinner parcel of the ting'd liquor that fill'd those bubbles, that that ting'd liquor must always appear Red, or of a Scarlet hue, since if Experiment be made, the quite contrary will ensue; for it is capable of being diluted into the palest Yellow.

Now, that I might avoid all the Objections of this kind, by exhibiting an Experiment that might by ocular proof convince those whom other reasons would not prevail with, I provided me a Prismatical Glass, Schem. 6.
Fig. 10.
made hollow, just in the form of a Wedge, such as is represented in the tenth Figure of the sixth Scheme. The two parallelogram sides ABCD, ABEF, which met at a point, were made of the clearest Looking-glass plates well ground and polish'd that I could get; these were joyn'd with hard cement to the triangular sides, BCE, ADF, which were of Wood; the Parallelogram base BCEF, likewise was of Wood joyn'd on to the rest with hard cement, and the whole Prismatical Box was exactly stopt every where, but onely a little hole near the base was left, whereby the Vessel could be fill'd with any liquor, or emptied again at pleasure.

One of these Boxes (for I had two of them) I fill'd with a pretty deep tincture of Aloes, drawn onely with fair Water, and then stopt the hole with a piece of Wax, then, by holding this Wedge against the Light, and looking through it, it was obvious enough to see the tincture of the liquor near the edge of the Wedge where it was but very thin, to be a pale but well colour'd Yellow, and further and further from the edge, as the liquor grew thicker and thicker, this tincture appear'd deeper and deeper, so that near the blunt end, which was seven Inches from the edge and three Inches and an half thick; it was of a deep and well colour'd Red. Now, the clearer and purer this tincture be, the more lovely will the deep Scarlet be, and the fouler the tincture be, the more dirty will the Red appear; so that some dirty tinctures have afforded their deepest Red much of the colour of burnt Oker or Spanish brown; others as lovely a colour as Vermilion, and some much brighter; but several others, according as the tinctures were worse or more foul, exhibited various kinds of Reds, of very differing degrees.

The other of these Wedges, I fill'd with a most lovely tincture of Copper, drawn from the filings of it, with spirit of Urine, and this Wedge held as the former against the Light, afforded all manner of Blues, from the faintest to the deepest, so that I was in good hope by these two, to have produc'd all the varieties of colours imaginable; for I thought by this means to have been able by placing the two Parallelogram sides together, and the edges contrary ways, to have so mov'd them to and fro one by another, as by looking through them in several places, and through several thicknesses, I should have compounded, and consequently have seen all those colours, which by other like compositions of colours would have ensued.

But insteed of meeting with what I look'd for, I met with somewhat more admirable; and that was, that I found my self utterly unable to see through them when placed both together, though they were transparent enough when asunder; and though I could see through twice the thickness, when both of them were fill'd with the same colour'd liquors, whether both with the Yellow, or both with the Blue, yet when one was fill'd with the Yellow, the other with the Blue, and both looked through, they both appear'd dark, onely when the parts near the tops were look'd through, they exhibited Greens, and those of very great variety, as I expected, but the Purples and other colours, I could not by any means make, whether I endeavour'd to look through them both against the Sun, or whether I plac'd them against the hole of a darkned room.

But notwithstanding this mis-ghessing, I proceeded on with my trial in a dark room, and having two holes near one another, I was able, by placing my Wedges against them, to mix the ting'd Rays that past through them, and fell on a sheet of white Paper held at a convenient distance from them as I pleas'd; so that I could make the Paper appear of what colour I would, by varying the thicknesses of the Wedges, and consequently the tincture of the Rays that past through the two holes, and sometimes also by varying the Paper, that is, insteed of a white Paper, holding a gray, or a black piece of Paper.

Whence I experimentally found what I had before imagin'd, that all the varieties of colours imaginable are produc'd from several degrees of these two colours, namely, Yellow and Blue, or the mixture of them with light and darkness, that is, white and black. And all those almost infinite varieties which Limners and Painters are able to make by compounding those several colours they lay on their Shels or Palads, are nothing else, but some compositum, made up of some one or more, or all of these four.

Now, whereas it may here again be objected, that neither can the Reds be made out of the Yellows, added together, or laid on in greater or less quantity, nor can the Yellows be made out of the Reds though laid never so thin; and as for the addition of White or Black, they do nothing but either whiten or darken the colours to which they are added, and not at all make them of any other kind of colour: as for instance, Vermilion, by being temper'd with White Lead, does not at all grow more Yellow, but onely there is made a whiter kind of Red. Nor does Yellow Oker, though laid never so thick, produce the colour of Vermilion, nor though it be temper'd with Black, does it at all make a Red; nay, though it be temper'd with White, it will not afford a fainter kind of Yellow, such as masticut, but onely a whiten'd Yellow; nor will the Blues be diluted or deepned after the manner I speak of, as Indico will never afford so fine a Blue as Ultramarine or Bise; nor will it, temper'd with Vermilion, ever afford a Green, though each of them be never so much temper'd with white.

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.

But because all those opacous colours have two kinds of beams or Rays reflected from them, that is, Rays unting'd, which are onely reflected from the outward surface, without at all penetrating of the body, and ting'd Rays which are reflected from the inward surfaces or flaws after they have suffer'd a two-fold refraction; and because that transparent liquors mixt with such corpuscles, do, for the most part, take off the former kind of reflection; therefore these colours mixt with Water or Oyl, appear much deeper than when dry, for most part of that white reflection from the outward surface is remov'd. Nay, some of these colours are very much deepned by the mixture with some transparent liquor, and that because they may perhaps get between those two flaws, and so consequently joyn two or more of those flaw'd pieces together; but this happens but in a very few.

Now, to shew that all this is not gratis dictum, I shall set down some Experiments which do manifest these things to be probable and likely, which I have here deliver'd.

For, first, if you take any ting'd liquor whatsoever, especially if it be pretty deeply ting'd, and by any means work it into a froth, the congeries of that froth shall seem an opacous body, and appear of the same colour, but much whiter than that of the liquor out of which it is made. For the abundance of reflections of the Rays against those surfaces of the bubbles of which the froth consists, does so often rebound the Rays backwards, that little or no light can pass through, and consequently the froth appears opacous.

Again, if to any of these ting'd liquors that will endure the boiling there be added a small quantity of fine flower (the parts of which through the Microscope are plainly enough to be perceiv'd to consist of transparent corpuscles) and suffer'd to boyl till it thicken the liquor, the mass of the liquor will appear opacous, and ting'd with the same colour, but very much whiten'd.

Thus, if you take a piece of transparent Glass that is well colour'd, and by heating it, and then quenching it in Water, you flaw it all over, it will become opacous, and will exhibit the same colour with which the piece is ting'd, but fainter and whiter.

Or, if you take a Pipe of this transparent Glass, and in the flame of a Lamp melt it, and then blow it into very thin bubbles, then break those bubbles, and collect a good parcel of those laminæ together in a Paper, you shall find that a small thickness of those Plates will constitute an opacous body, and that you may see through the mass of Glass before it be thus laminated, above four times the thickness: And besides, they will now afford a colour by reflection as other opacous (as they are call'd) colours will, but much fainter and whiter than that of the Lump or Pipe out of which they were made.

Thus also, if you take Putty, and melt it with any transparent colour'd Glass, it will make it become an opacous colour'd lump, and to yield a paler and whiter colour than the lump by reflection.

The same thing may be done by a preparation of Antimony, as has been shewn by the Learned Physician, Dr. C.M. in his Excellent Observations and Notes on Nery's Art of Glass; and by this means all transparent colours become opacous, or ammels. And though by being ground they lose very much of their colour, growing much whiter by reason of the multitude of single reflections from their outward surface, as I shew'd afore, yet the fire that in the nealing or melting re-unites them, and so renews those spurious reflections, removes also those whitenings of the colour that proceed from them.

As for the other colours which Painters use, which are transparent, and us'd to varnish over all other paintings, 'tis well enough known that the laying on of them thinner or thicker, does very much dilute or deepen their colour.

Painters Colours therefore consisting most of them of solid particles, so small that they cannot be either re-united into thicker particles by any Art yet known, and consequently cannot be deepned; or divided into particles so small as the flaw'd particles that exhibit that colour, much less into smaller, and consequently cannot be diluted; It is necessary that they which are to imitate all kinds of colours, should have as many degrees of each colour as can be procur'd.

And to this purpose, both Limners and Painters have a very great variety both of Yellows and Blues, besides several other colour'd bodies that exhibit very compounded colours, such as Greens and Purples; and others that are compounded of several degrees of Yellow, or several degrees of Blue, sometimes unmixt, and sometimes compounded with several other colour'd bodies.

The Yellows, from the palest to the deepest Red or Scarlet, which has no intermixture of Blue, are pale and deep Masticut, Orpament, English Oker, brown Oker, Red Lead, and Vermilion, burnt English Oker, and burnt brown Oker, which last have a mixture of dark or dirty parts with them, &c.

Their Blues are several kinds of Smalts, and Verditures, and Bise, and Ultramarine, and Indico, which last has many dirty or dark parts intermixt with it.

Their compounded colour'd bodies, as Pink, and Verdigrese, which are Greens, the one a Popingay, the other a Sea-green; then Lac, which is a very lovely Purple.

To which may be added their Black and White, which they also usually call Colours, of each of which they have several kinds, such as Bone Black, made of Ivory burnt in a close Vessel, and Blue Black, made of the small coal of Willow, or some other Wood; and Cullens earth, which is a kind of brown Black, &c. Their usual Whites are either artificial or natural White Lead, the last of which is the best they yet have, and with the mixing and tempering these colours together, are they able to make an imitation of any colour whatsoever: Their Reds or deep Yellows, they can dilute by mixing pale Yellows with them, and deepen their pale by mixing deeper with them; for it is not with Opacous colours as it is with transparent, where by adding more Yellow to yellow, it is deepned, but in opacous diluted. They can whiten any colour by mixing White with it, and darken any colour by mixing Black, or some dark and dirty colour. And in a word, most of the colours, or colour'd bodies they use in Limning and Painting, are such, as though mixt with any other of their colours, they preserve their own hue, and by being in such very smal parts dispers'd through the other colour'd bodies, they both, or altogether represent to the eye a compositum of all; the eye being unable, by reason of their smalness, to distinguish the peculiarly colour'd particles, but receives them as one intire compositum: whereas in many of these, the Microscope very easily distinguishes each of the compounding colours distinct, and exhibiting its own colour.

Thus have I by gently mixing Vermilion and Bise dry, produc'd a very fine Purple, or mixt colour, but looking on it with the Microscope, I could easily distinguish both the Red and the Blue particles, which did not at all produce the Phantasm of Purple.

To summ up all therefore in a word, I have not yet found any solid colour'd body, that I have yet examin'd, perfectly opacous; but those that are least transparent are Metalline and Mineral bodies, whose particles generally, seeming either to be very small, or very much flaw'd, appear for the most part opacous, though there are very few of them that I have look'd on with a Microscope, that have not very plainly or circumstantially manifested themselves transparent.

And indeed, there seem to be so few bodies in the world that are in minimis opacous, that I think one may make it a rational Query, Whether there be any body absolutely thus opacous? For I doubt not at all (and I have taken notice of very many circumstances that make me of this mind) that could we very much improve the Microscope, we might be able to see all those bodies very plainly transparent, which we now are fain onely to ghess at by circumstances. Nay, the Object Glasses we yet make use of are such, that they make many transparent bodies to the eye, seem opacous through them, which if we widen the Aperture a little, and cast more light on the objects, and not charge the Glasses so deep, will again disclose their transparency.

Now, as for all kinds of colours that are dissolvable in Water, or other liquors, there is nothing so manifest, as that all those ting'd liquors are transparent; and many of them are capable of being diluted and compounded or mixt with other colours, and divers of them are capable of being very much chang'd and heightned, and fixt with several kinds of Saline menstruums. Others of them upon compounding, destroy or vitiate each others colours, and precipitate, or otherwise very much alter each others tincture. In the true ordering and diluting, and deepning, and mixing, and fixing of each of which, consists one of the greatest mysteries of the Dyers; of which particulars, because our Microscope affords us very little information, I shall add nothing more at present; but onely that with a very few tinctures order'd and mixt after certain ways, too long to be here set down, I have been able to make an appearance of all the various colours imaginable, without at all using the help of Salts, or Saline menstruums to vary them.

As for the mutation of Colours by Saline menstruums, they have already been so fully and excellently handled by the lately mention'd Incomparable Authour, that I can add nothing, but that of a multitude of trials that I made, I have found them exactly to agree with his Rules and Theories; and though there may be infinite instances, yet may they be reduc'd under a few Heads, and compris'd within a very few Rules. And generally I find, that Saline menstruums are most operative upon those colours that are Purple, or have some degree of Purple in them, and upon the other colours much less. The spurious pulses that compose which, being (as I formerly noted) so very neer the middle between the true ones, that a small variation throws them both to one side, or both to the other, and so consequently must make a vast mutation in the formerly appearing Colour.

http://ebooks.adelaide.edu.au/h/hooke/robert/micrographia/observ10.html

Last updated Monday, March 17, 2014 at 16:42