DEFECTS IN PRINTS.
The bath solution is sometimes repelled by the paper, and this is found
chiefly in highly albumenized paper, and is generally caused by the
paper being too dry. Passing the sheet of paper over the steam from a
saucepan will generally effect a cure.
Small white spots, with a black central pin-point, are often met with in
prints. Dust on the paper during sensitizing will cause them, the grit
forming a nucleus for a minute bubble. All paper should be thoroughly
dusted before being floated on the sensitizing bath.
Grey, star-like spots arise from small particles of inorganic matter,
such as ferric oxide, lime, &c., which are present in the paper. They
become more apparent by decomposition during the printing operations.
They may generally be discernible by examining the paper by transmitted
light.
Bronze lines (straight) occur through a stoppage during floating the
paper in the sensitizing solution. Should the lines be irregular,
forming angles and curves, it is probable that a scum of silver oxide,
&c., may be detected on the surface of the sensitizing solution. A strip
of blotting-paper drawn across the bath will remove the cause of the
defect.
Should the print appear marbled, it may be surmised that the sensitizing
solution is weak, or that the paper has not been floated sufficiently.
In some cases it may arise from imperfect albumenizing; but in ordinary
commercial samples the cause can be easily traced.
Red marks on the shadows may appear during toning, and are very
conspicuous after fixing. They generally arise from handling the paper
with hot, moist fingers after sensitizing; greasy matter being deposited
on the surface, prevents the toning bath acting properly on such parts.
Weak prints are generally caused by weak negatives. Such can be
partially remedied by paying attention to the strength of the
sensitizing bath (see Appendix), and by using washed paper.
Harsh prints are due to harsh negatives. They can generally be remedied
by paying attention to the mode of printing, as given in Chapter IX. If
the negative be under-exposed and wanting in detail, there is, however,
no cure for this defect.
A red tone is due to insufficient toning; whilst a poor and blue tone is
due to an excess of toning.
The whites may appear yellow from imperfect washing, imperfect toning,
imperfect fixing, or from the use of old sensitized paper.
Should prints refuse to tone, either the gold has been exhausted, or
else a trace of sodium hyposulphite has been carried into the toning
bath by the fingers or other means. A trace of hyposulphite is much more
injurious to the print than a fair quantity of it. Should the toning
bath refuse to tone after the addition of gold, it may be presumed that
it is contaminated by a trace of sodium hyposulphite.
A dark mottled appearance in the body of the paper indicates imperfect
fixing, combined with the action of light on the unaltered chloride
during fixing. If the fixing bath be acid, the excess of acid combines
with the sulphur, and forms hydrosulphuric acid, which will also cause
the defect.
The cause of mealiness or "measles" in the print has been explained in
page 32.