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Micrographia by Robert Hooke

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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_, 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 _laminae_ 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.

* * * * *


Observ. XI. _Of _Figures_ observ'd in small Sand._

Sand generally seems to be nothing else but exceeding small Pebbles, or at
least some very small parcels of a bigger stone; the whiter kind seems
through the _Microscope_ to consist of small transparent pieces of some
_pellucid_ body, each of them looking much like a piece of _Alum_, or _Salt
Gem_; and this kind of Sand is angled for the most part irregularly,
without any certain shape, and the _granules_ of it are for the most part
flaw'd, through amongst many of them it is not difficult to find some that
are perfectly _pellucid_, like a piece of clear Crystal, and divers
likewise most curiously shap'd, much after the manner of the bigger
_Stiriae_ of Crystal, or like the small Diamants I observ'd in certain
Flints, of which I shall by and by relate; which last particular seems to
argue, that this kind of Sand is not made by the comminution of greater
transparent Crystaline bodies, but by the _concretion_ or _coagulation_ of
Water, or some other fluid body.

There are other kinds of courser Sands, which are browner, and have their
particles much bigger; these, view'd with a _Microscope_, seem much courser
and more _opacous_ substances, and most of them are of some irregularly
rounded Figures; and though they seem not so _opacous_ as to the naked eye,
yet they seem very foul and cloudy, but neither do these want curiously
transparent, no more than they do regularly figur'd and well colour'd
particles, as I have often found.

There are multitudes of other kinds of Sands, which in many particulars,
plainly enough discoverable by the _Microscope_, differ both from these
last mention'd kinds of Sands, and from one another: there seeming to be as
great variety of Sands, as there is of Stones. And as amongst Stones some
are call'd precious from their excellency, so also are there Sands which
deserve the same Epithite for their beauty; for viewing a small parcel of
_East-India_ Sand (which was given me by my highly honoured friend, Mr.
_Daniel Colwall_) and, since that, another parcel, much of the same kind, I
found several of them, both very transparent like precious Stones, and
regularly figur'd like Crystal, _Cornish_ Diamants, some Rubies, &c. and
also ting'd with very lively and deep colours, like _Rubys_, _Saphyrs_,
_Emeralds_, &c. These kinds of granuls I have often found also in _English_
Sand. And 'tis easie to make such a counterfeit Sand with deeply ting'd
Glass, Enamels and Painters colours.

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