WASHING THE PRINT.
There are very many apparatus designed for washing prints; but
we believe that, where few prints have to be treated, careful
hand-washing is as superior to machine-washing, as hand-made paper
is to machine-made. In our own practice we take the prints from the
fixing-dish, and immerse them in a large puncheon of water, and allow
them to soak for five minutes, after which we carefully pour off all
the water, and replenish with fresh, in which we leave them for a
quarter-of-an-hour. After that we take the prints and place them on a
glass slab, and, with a squeegee, squeeze as much water as possible out
of each separately; this we repeat twice. After two more washings of a
quarter-of-an-hour, we then wash for half-an-hour, and, with a sponge,
dab them as dry as possible, and again immerse for half-an-hour. After
repeating this operation twice, we allow a stream of running water
to pour into the puncheon for a couple of hours, carrying the stream
through an india-rubber pipe, at the end of which is a glass tube, to
the bottom of the puncheon, and so that the pour of water goes against
the side. By this means there is a constant stir in the water, and the
water flows over the edge of the puncheon. It is convenient to cut a
notch in the top rim of the puncheon, so that the water may find an exit
before reaching the level of the rim. The prints are then taken out,
sponged once more, and dried. By this arrangement we have got prints
which are perfectly unfaded, though they have been in existence eighteen
years, and have been to the tropics, and in the dampest climates. This
method of washing, though tedious, should be applied to all prints; but,
in the present day, it can hardly be hoped that it can be immediately
adopted, on account of the attention it requires; we therefore describe
an apparatus which can be used. It was designed by Mr. England,
and consists of a working trough, as shown in the figure, which is
automatically worked by an overshot wheel. We need not enter into the
details of the invention, as they are self-evident.
[Illustration: _Fig._ 28.]
This washing arrangement causes the prints to be alternately soaking
in water, and draining. Whilst in the water they are perpetually being
shaken apart by the movement of the tray, and thus every part of the
print gets washed, and it is almost impossible for two prints to stick
together. In all washing apparatus there is a danger of air-bells
forming on the surface of the prints while in the water, but in this
form there is the advantage that whilst draining the air-bells must
break, and so water on rising to the level of the prints can obliterate
any of the evil effects which would be caused by their being perpetually
remaining on one spot. It is useless to attempt to describe other forms
of the apparatus, since there are so many; we have chosen one which
appears to us to be a satisfactory form.
The following tests for the elimination of hyposulphite are taken from
another work of this series.[26]
"The following is a most delicate test.
"Make the following test solution:--
Potassium permanganate 2 grains
Potassium carbonate 20 "
Water 1 quart
"The addition of a few drops of this rose-coloured solution to a pint of
water will yield a slightly pink tinge. If there be any trace of sodium
hyposulphite present, this colour will give place to one of a greenish
hue.
"If the permanganate be not at hand, the following well-known starch
iodide test may be adopted:--
"Take about two drachms of water and a small piece of starch about the
size of a small pea; powder and boil the starch in the water till the
solution is quite clear; add one drop of a saturated solution of iodine
in alcohol to this clear liquid. It will now become dark blue. Of this
solution drop two drops into two clean test tubes, and fill up one with
distilled water and the other with the water to be tested; a faint blue
colour should be perceptible in the first test tube. In the second
test tube, should hyposulphite be present, this blue colour will have
disappeared, the iodide of starch becoming colourless in its presence.
The best mode of comparing the two waters is by placing a piece of white
paper behind the test tubes.
"It frequently occurs that though sodium hyposulphite cannot be detected
in the washing water, it may be present in the paper itself. The paper
on which most prints are taken being sized with starch, if a _very_
weak solution of iodine be applied with a brush across the _back_ of a
print, a blue mark will indicate the _absence_ of the hyposulphite. Care
must be taken that the iodine solution is _very_ weak, otherwise a part
of the iodine will first destroy the trace of the salt, and then the
remainder will bring out the blue re-action."
We finish this chapter by quoting our maxims to be observed in printing.
"_Maxims for Printing._
"1. The prints should have the highest lights _nearly_ white,
and the shadows verging on a bronzed colour before toning.
"2. Place the prints, before toning, in the water, face
downwards, and do not wash away too much of the free nitrate of
silver.
"3. The toning solution must be neutral or slightly alkaline,
and not colder than 60°.
"4. Tone the prints to purple or sepia, according as warm or
brown prints are required.
"5. Move the prints, in both the toning and fixing solutions,
repeatedly, taking care that no air-bubbles form on the surface.
"6. Take care that the fixing bath is not acid.
"7. Use fresh sodium hyposulphite solution for each batch of
prints to be fixed.
"8. Wash thoroughly after and before fixing.
"9. Make a sensitizing bath of a strength likely to give the
best results with the negatives to be printed.
"10. Print in the shade, or direct sunshine, according to the
density of the negative."