ing, as if it is quite dry the
printing will be very slow and irregular. The best conditions for the
preparation of the paper have scarcely been decided upon yet, and it
is not quite fair to judge the process. The prints are cleared in the
acid baths and washed for about a quarter of an hour.

The sepia and black hot bath processes are much alike in the general
treatment. There are, however, some special precautions to be observed
with the sepia paper, the chief being to protect it from any but the
faintest rays of light; the prints, unlike the black ones, may be
affected by light when in the acid bath. A special solution must be
added to the developer to keep the lights pure. Over-exposure cannot
be corrected by using a cooler bath, as is the case with the black
prints, and the paper does not remain good so long.

The paper for the black prints by the hot bath process is washed with
a mixture of potassic platinous chloride and ferric oxalate, the
proportion being about sixty grains of the platinum salt to one ounce
of the iron solution. It will not keep good longer than twenty minutes
or so, and must be applied to the paper directly after mixing. The
ferric oxalate in the paper is reduced by the action of light to
ferrous oxalate, which forms the faint visible image; this, when the
paper is floated on the oxalate of potash bath, is capable of reducing
the platinum salt in contact with it into metallic platinum; but the
ferric salt, which remains unaltered, has no action on the platinum
salt, leaving these parts, which represent the high lights of the
print, untouched. The ferric oxalate is removed by the acid baths
which follow the development. A good temperature for development is
150 deg. Fahr., and when using this so much detail should not be apparent
as when printing for the cold bath process, in which all the detail
desired should be very faintly visible. There are, however, many
methods of exposing the paper and developing it, and no fixed rule can
be made, but the development must in every case be suited to the
exposure or the result will be a failure. For instance, the paper may
be printed until all detail is visible, but a very much cooler
development must be used, say 80 deg. or 90 deg.; on the other hand, a
slightly short exposure may be given, and a temperature of 180 deg. to
200 deg. used. 150 deg. should be taken as the normal temperature, and kept to
until some experience has been gained, as employing a