Transcriber's Note:
Inconsistent numbering of figures and references to figures have been
retained as in the original publication.
[Illustration: A Specimen of Woodburytype Printing.]
THE ART AND PRACTICE OF SILVER PRINTING.
BY
H. P. ROBINSON & CAPT. ABNEY, R.E., F.R.S.
THE AMERICAN EDITION,
NEW YORK:
E. & H. T. ANTHONY & CO., NO. 591 BROADWAY.
1881.
PREFACE.
Silver printing has been often doomed, but it still survives. Other
processes of photographic printing have been introduced, nearly all of
them having their individual merits, especially that of permanency, but
all lacking in two essential qualities--ease of production and beauty
of result. In these particulars no process has ever approached the one
to the working of which this little book is devoted. The one defect of
silver printing is the possibility of its results fading; but surely
it is better to be beautiful, if fading, than permanent and ugly. It
is better to be charmed with a beautiful thing for a few years, than
be bored by an ugly one for ever. But is silver printing necessarily
a fading process? We have in our possession a large number of silver
photographs produced from twenty to twenty-five years ago, which are
as perfect in tone and colour as when they were produced. Carefully
prepared, and properly kept, a silver print should be as permanent as
any other. That silver prints should be permanent as well as beautiful,
has been the object of
THE AUTHORS.
TABLE OF CONTENTS.
CHAPTER PAGE
I.--Preliminary Experiments 1
II.--Preparation of Albumenized Paper 6
III.--The Sensitizing Bath 13
IV.--How to Keep the Sensitizing Bath in Order 20
V.--Silvering the Paper 26
VI.--Washed Sensitive Paper 31
VII.--Cutting Paper 36
VIII.--Printing-Frames 42
IX.--Preparing the Landscape Negative 45
X.--Printing the Landscape 49
XI.--Preparing the Portrait Negative 57
XII.--Vignetting 60
XIII.--Printing the Portrait 69
XIV.--Combination Printing 74
XV.--Toning 85
XVI.--Fixing the Print 92
XVII.--Washing the Print 95
XVIII.--Printing on Plain Paper 99
XIX.--Printing on Resinized Paper 100
XX.--Printing on Gelatino-Chloride Emulsion Paper 103
XXI.--Drying the Prints 105
XXII.--Mounting Photographs 110
XXIII.--Defects in Prints 115
XXIV.--Encaustic Paste 117
XXV.--Enamelling Prints 119
XXVI.--Cameo Prints 121
Appendix 123
CHAPTER I.
THEORY OF SILVER PRINTING.
Perhaps it may be wise, first of all, to give the reader some account
of the manner in which the subject of silver printing is to be treated,
before entering into very minute details, so that it may be followed
as a whole, instead of being studied in fragments, a course which is
sure to lead to failure, from a want of comprehending what may have
been skipped. To understand "the why" and "the wherefore" of every
detail is an essential in most occupations, and it is wonderful that
photographers are satisfied with the results of rule-of-thumb formulæ,
instead of reasoning out their utility. In the following pages most of
the theoretical considerations will be brought out in such a manner that
everyone will be able to understand them, provided only that there is a
slight acquaintance with the name and properties of the chemicals which
are dealt with.
PRELIMINARY EXPERIMENTS.
Into a glass beaker put a couple of pinches of common salt, which must
be dissolved in a little water.
In a test-tube[1] dissolve about an equal amount of silver nitrate
(AgNO_{3}), and add it to the salt solution. We shall find that we
have an immediate precipitate, for chloride of silver will be formed
by what is called double[2] decomposition, and there will remain in
solution a soluble salt known as sodium nitrate. When the silver
chloride has settled down, decant off the liquid, and add water to it
once or twice, draining off each time. Divide the chloride into four
parts, placing each part on a strip of glass. On two of them pour a
little common salt solution, and on the other two pour a little solution
of silver nitrate; take one of each pair, and place it in a dark
cupboard (if warmed, the quicker will be the operation) to dry. Take
the other two moist portions of chloride into the open air, and expose
them to daylight, and note the results. It will be seen that one of
these will darken very rapidly to a violet colour, whilst the other will
remain much lighter, though perceptibly blackening. After a time the
latter will appear to grow deeper, whilst the former will become a deep
black. The one that blackens most rapidly will be found to be that one
on which the silver nitrate was poured. Divide the slightly blackened
chloride on the strip of glass into two portions, and over one pour a
little beer, and over the other a weak solution of potassium nitrite,
and again note the difference. It will be found that here the blackening
commences anew, but proceeds much more rapidly on that portion over
which the nitrite was poured. Here are the experiments. What do they
teach?
Potassium nitrite, and silver nitrate, are both inorganic salts, and
they both have an affinity for--that is, tend to combine with--any
of the halogens (by which are meant such bodies as chlorine, iodine,
bromine, and fluorine). In the former case we have silver chloride
formed with a little hypo-chlorous acid; in the latter we have a more
difficult decomposition: the potassium nitrite is decomposed into
hydrochloric acid and potassium nitrate.[3]
We can tell that chlorine is liberated by the action of light on silver
chloride, since if we prepare some as above, well wash it, and expose it
to light in pure water, we shall find that the latter contains chlorine,
since a few drops of silver nitrate poured into it after exposure give a
white precipitate.
If we make the same experiments with the dried portions of silver
chloride as we did with the moist, we shall obtain the same results,
with the exception that with the dried, in which there is excess of
salt, there will be hardly any discolouration. The experimentalist
should also note that if the darkened chloride be broken up, the
interior retains its white colour in all its purity. This tells us that
the discolouration is _almost_ confined to the surface, hence it is
useless, for printing purposes, to have such a mass of chloride as would
be opaque, since all but a very thin film would be unacted upon.
If the darkened chloride be examined closely, it will be seen that
the colour varies, being bluer in the case of that which has silver
nitrate in contact with it (either moist or dry) as compared with that
which is darkened in contact with the potassium nitrite. We have the
best of reasons for believing that the blue colour is really due to a
combination between the sub-chloride and the oxygen contained in the
water or in the air. The true colour of the sub-chloride is that which
is exposed beneath an oxygen absorbent such as the nitrite.
Practical printers are aware that albumenized paper containing a
chloride is employed for producing silver prints, and the probability is
that the albumen must exercise some kind of influence on the resulting
picture. Let us examine this, and see what effect it can have. Carefully
break an egg, and separate the yolk from the white, pouring the latter
into a beaker. Beat up the white with a bundle of quill pens, allow the
froth to subside, and then filter it. Pour a little of the filtered
albumen (the white of egg) into a test-tube, and add a little silver
nitrate solution to it, and expose the precipitate which falls to light.
It will be seen that it darkens rapidly, assuming a foxy red colour.
Take a couple of glass plates and coat them with plain collodion, wash
under the tap, and whilst still moist flow albumen over them two or
three times, and set them up to dry. When thoroughly dry, plunge them
for a few seconds into a weak solution of silver nitrate (30 grains
to the ounce of water will suffice), wash one under the tap, and then
allow both to dry again. Take both plates out into the light, and note
the results. The one from which the silver nitrate has not been washed
will darken very rapidly, the other will take some time to start; but if
the exposure be sufficiently prolonged, it will gradually assume a hue
equally as dark as the other.
If we repeat these experiments with gelatine, which is used as a sizing
in some papers, we shall find very much the same nature of things taking
place, the differences being so slight, however, as not to require
detailed notice.
So far, then, we have considered the darkening properties of the silver
compounds which are to be used by the printer, but it remains to be
seen what _permanency of darkening_ they possess. If we treat the
darkened silver chloride solution exposed with the silver nitrate or
the potassium nitrite to a solution of hyposulphite of soda or ammonia,
both of which are solvents of the white chloride, we shall find that
a residue of metallic silver is left behind. If we treat the darkened
albuminate of silver with the same agents, we shall find that very
little change is effected by them.
From this we may gather that the action of light on them is of a totally
different nature.[4] This is also most marked if we treat the two with
hydrosulphuric acid solution (sulphuretted hydrogen[5]). It will be
found that the colour of the darkened silver chloride becomes more
intense, while the other is bleached, or, rather, becomes of a yellow
tint. This last effect has an important bearing on the permanency of
silver prints, as will be more fully explained when considering the
subject of fixing the print.