; 6* I N K. 
been burnt; 'but fbis mull neceffarily be a bad practice, 
as fucb oii. is apt to go through the paper ; a fault very 
common in prints," efpecially if the paper is not very- 
thick. No foap is added ; becaufe the ink is not cleared 
off from the copper-plates with alkaline ley as in com¬ 
mon printing, but with a brufti dipped in oil. 
The following receipt for making copper-plate ink is 
copied from the Handmaid to the Arts.—Take any quan¬ 
tity of the bell nut-oil, and put it into an iron pot with 
a cover well fitted to it, of which pot it muft fill only 
two-thirds. Place it on a fire, and, having put on the 
cover, let it continue in that ftate till it makes an ebulli¬ 
tion, when it muft be very well ftirred to prevent its boil¬ 
ing over. Suffer it then to catch fire, or kindle it by a 
lighted paper; and when it flames take it from the fire, 
and place it in a corner of the chimney, where let it con¬ 
tinue to burn half an hour, frequently ftirringit. You 
may then extinguish the flame, by putting the cover on 
the pot; or, if that be not effectual, by putting a wet 
cloth over it. This produces the weak oil which has the 
principal part in the compofition of the ink. But a ftrong 
oil muft likewife be prepared by the fame means; only, 
inftead of extinguiftiing the flame at the end of half an 
hour, it muft be continued till the oil be rendered very 
thick and glutinous, which muft be examined by taking 
a little out of the pot, and fuffering it to cool; .when, if 
it be found to be extremely adhefive and ropy, fo as to 
be drawn out in long threads, it is fufficiently burnt, and 
the flame muft be put out. This is the ftrong oil, of 
which a proportion is to be ufed along with the other in 
the printing-ink. Having prepared thefe oils, take half 
a pound of the Frankfort or any other good black, and 
grind it with the addition of only fo much of the weak 
oil as is neceffary to make it work on the ftone, which 
will be generally fomething lefs than half the weight. 
The whole being firft incorporated together, and after¬ 
wards thoroughly well mixed by a fecond grinding, (hav¬ 
ing only a fmall quantity on the ftone at a time,) a quan¬ 
tity of the ftrong oil muft be added, which may be as 
much as is equal to the fize of a fmall hen’s egg. It will 
then be fit for ufe, and muft be put into a proper pot, 
and covered wdth paper or leather. There are fome who 
add an onion or cruft of bread to the oil while boiling, 
in order to take off the greafinefs; but the burning will 
fufficiently do that office when properly managed. In- 
Read of Frankfort or other kinds of black commonly 
ufed, the following compofition may be fubftituted, and 
will form a much deeper and more beautiful black than 
can be obtained by any other method : Take of the deep- 
eft Pruffian blue five parts, and of the deepeft-coloured 
lake and brown pink each one part. Grind them well 
with oil of turpentine, and afterwards with the ftrong 
and weak oils in the manner and proportion above direft- 
ed. The colours need not be bright for this purpofe, but 
they fhould be the deepeft of the kind, and perfectly tranf- 
parent in oil, as the whole effect depends on that quality. 
Under this head we may notice the Jluchum, or perpe¬ 
tual ink of the ancients, for engraving letters on ftone.— 
This ink (as it is called from its application) was formed 
by mixing about three parts of pitch with one part of 
lamp-black, and making them incorporate by melting the 
pitch. With this compofition, ufed in a melted ftate, the 
letters were filled, and would, without extraordinary vio¬ 
lence, endure as long as the ftone itfelf. 
Of SYMPATHETIC INK for SECRET WRITING, 
Here the objeft is to compofe a liquid with which a 
perfon may write, and yet nothing appear on the paper 
after it is dry, till fome means are ufed, as holding the pa¬ 
per to the fire, rubbing it over with fome other liquor, &c. 
Thefe kinds of ink may be divided into feven claffes, 
with refpect to the means ufed to make them vilible. 
i. Such as become vijible by faffing another liquor over them, 
er by expofng them to the vapour of that liquor. —This firft clafs 
contains four kinds of ink, viz, folutions of lead, bif- 
muth, gold, and green vitriol, or fulphat of iron. The 
firft two become vifible by the contact of lulphureous li¬ 
quids or fumes. For the firft, a foiution of common fu- 
gar of lead in water anfvvers very well. With this folu- 
tion write with a clean pen, and the writing when dry 
will be totally invifible; but if it be wetted with a foiu¬ 
tion of hepar fulphuris, or of orpiment, diffolved by means 
of quicklime, or expofed to the ftrong vapours of thefe 
folutions, the writing will appear of a brown colour, 
more or lefs deep according to the ftrength of the fulpliu- 
reous fume. The vapours of this tincture are fo exceed¬ 
ingly penetrating, that it is laid they will even penetrate 
through a wall, fo as to make a writing with faccharum 
faturni appear legible on the other fide ; but this is much 
to be doubted. It is even faid that it cannot penetrate 
through the fubftance of paper, but only infinuates itfelf 
betwixt the leaves; and hence, if the edges of the leaves 
are glued together, no black colour will appear. By the 
fame means the foiution of nitrat of bifmuth will appear 
of a deep black. 
The fympathetic ink prepared from gold depends on 
the property by which that metal precipitates from its 
folvent on the addition of a foiution*of tin. Write with 
a foiution of gold in nitro-muriatic acid, and let the pa¬ 
per dry gently in the fliade; nothing will appear for the 
firft feven or eight hours. Dip a pencil in the foiution 
of tin, and, drawdng it lightly over the invifible charac¬ 
ters, they will immediately appear of a purple colour. 
Peter Borel, in a book called Hijloriarum et Obfervationum 
medico-phyfic. printed at Paris, firft in 1653, and afterwards 
in 1657, gives a receipt for making an ink, which he calls 
magnetic waters which a6l at a dijlancc. The receipt is as 
follows : “Let quicklime be quenched in common water, 
and, while quenching, let fome orpiment be added to it; 
(this, however, ought to be done by placing warm afnes 
under it for a whole day ;) and let the liquor be filtered, 
and preferved in a glafs bottle well corked. Then boil 
litharge of gold, well pounded, for half an hour with vi¬ 
negar, in a brafs veffel, and filter the whole through pa¬ 
per, and preferve it alfo in a bottle clofely corked. If 
you write any thing with this laft water, with a clean 
pea, the writing will be invifible when dry; but if it be 
waflied over with the firft water it will become inftantly 
black. In this, however, there is nothing aftonilfiing; 
but this is wonderful, that though flieets of paper with¬ 
out number, and even a board, be placed between the in¬ 
vifible writing and the fecond liquid, it will have the’lkme 
effeft, and turn the writing black, penetrating the wood 
and paper without leaving any traces of its adtion, which 
is certainly furprifing ; but the fetid fmell, occafioned by 
the mutual aftion of the liquids, deters many from making 
the experiment, I am, however of opinion, that I could 
improve this fecret by a more refined chemical prepara¬ 
tion, fo as that it fhould perform its effeft through a 
wall. This fecret (fays Borel) I received, in exchange 
for others, from J. Brofton, a learned and ingenious apo* 
thecary of Montpelier.” Beckman vol. i. 
Charafters w’ritten with a foiution of green vitriol will 
likewife be invifible when the paper is dry ; but, if wetted 
with an infufion of galls, they will immediately appear as 
if written with common ink. Thofe who have obferved 
that the ingredients of common ink are nothing more 
than green vitriol and nut-galls, will readily fee, that in 
this cafe the ink has been formed on the paper. In the 
making of ink, the two ingredients are combined before 
they are ufed for writing; here, they are not combined 
till the writing is finiflied ; this is the whole difference. 
If you are defirous of having an ink that (hall become 
blue, you muft write with a foiution of green vitriol, and 
moiften the writing with the liquor which forms Pruffian 
blue, the compofition of which is fhown in the article 
Chemistry, vol.iv. p. 300. 
z. Thofe that do not appear fo long as they are kept clofe, 
but foon become vifible on being expofed to the air. —To this fe- 
CQJid clafs belong the folutions of all thofe metals which 
ars 
