:
PHOTOGRAPHIC CHEMICALS AND SOLUTIONS
244
The question
is
often asked, therefore,
if it is
better to develop for a
longer time in a non-staining developer like Elon-hydroquinone or for
a shorter time in a staining pyro developer.
If it
necessary always to
is
duplicate results as in the case of developing motion picture film in a
deep tank, a non-staining developer conditions
it is
is
desirable because under these
impossible to duplicate results with a staining developer
as explained below.
—
Control of Developer Stain. It is practically impossible to obimage which is free from general stain and vice versa. The proportion of general stain to image stain depends on the following tain a stain
factors a.
The quantity
of sulphite or preservative in the developer.
greater the quantity of sulphite present, the less
and vice
is
The
the stain produced
versa.
If the
developer
is
old, it rapidly
produces general stain with
little
becomes highly colored and then
or no silver or stain image, because the
developer has been converted largely to oxidation products which will not develop an image. b.
The time
of rinsing between developing
and
fixing.
A
long rinse
permits further oxidation of the developer by the oxygen dissolved in the
wash water and
c.
The nature
this
produces general stain. Since sulphite or bisulphite bleaches
of the fixing bath.
out stain and prevents oxidation of the developer, an acid fixing bath, therefore, destroys both general stain
order to produce the
maximum
and the stain image.
Hence,
in
quantity of stain image, use a fresh
developer containing low sulphite, rinse quickly between developing and fixing,
and
The
fix in
a large volume of fresh hypo.
following pyro formula
when used
image with a minimum of general
good stain
Pyro-Stain Developer
[SD-1] Water (about
Sodium
Avoirdupois 16 ounces
125° F.) (52° C.)
Sulphite, desiccated
20 40 75 32
Pyro
Sodium Carbonate,
desiccated
Water to make
Develop fix in
fresh will give a
stain.
for 6
minutes at 65 °F. (i8°C.)
Metric 500.0 cc
grams grams grams
grains grains grains
1.4 2.8 5.3
ounces
1.0 liter
in a shallow tray, rinse
and
a plain hypo bath.
The above
reasons explain
on a practical scale such as
why
it is
in small
impossible to produce pyro stain
amateur tanks or
in
deep tanks.
As
the developer becomes older the proportion of oxidation stain to stain
image changes, which
in turn
changes the quality of the negative.