Evening star., 1948-05-23
Camera Angles

the process, DaguerTe mace pup
lie disclosure before the French
Academy of Science after securing
a. contract from his government
which granted him an annuity for
life.
According to an early text on the
subject by Sir william Abney, the
daguerreotype process was as fol-
lows:
1.-THE process consists Of the
formation of a sensitive surface of
silver idodide, or silver iodine and
bromide on silver plate by means
of the direct action of iodine, or
iodine and bromide. One Of the
most difficult (because great clean
illness in every detail is required)
parts of the whole process Is
the preparation of the silvered sur
face before its coming into contact
with the halogen. The plates are
usually copper, on which a film OF
metallic silver is deposited, and when
they leave the silvering solution
have, as a rule, a frosted appear
ance. After being cut to the proper
size they are ready for polishing.
Polishing the Plates.
"A plate in this state may be
placed on a fiat table and four thin
strips of wood nailed around 1t to
prevent slipping. To the surface is
then applied tripoli powder in alco-
| hol with canton flannel and
worked to such an extent that 1t is
perfectly free from scratches and
is fairly smooth. Polishing is ef-
fected by means of buff. This IS
made by inclosing a wooden ball, of
the size of a small apple, in skin
of felt and then of cotton wool.
Over this is stretched a piece of
the finest chamois leather. Onto
the surface of the silver Is then
scattered a small quantity Of jew
eler's rouge and the buff is caused
to travel over the plate from end
to end and side to side alternately
till it becomes of the highest polish.
This polishing should take place
almost Immediately before the SEN
stitizing operation is commenced,
otherwise there is a liability Of the
surface obtaining impurities from
the atmosphere.
"A two-chambered sensitizing box
is required-one chamber above the
other and separated by piece of
cardboard. In the bottom chamber
is placed iodine in powder. The
iodine will volatiliZe at ordinary
temperatures and condense on the
surface of the cardboard next to 1t.
When a plate is to be sensitized the
cardboard is reversed and the iodine
volatilizes from the top surface to
the silver plate. The plate gradu-
ally receives q thin coating Of
iodine, passing through various
stages of color. When q ruddy
color is reached, 1t is placed in a
similar box to that already de-
scribed (omitting the cardboard) at
the bottom Of which is a mixture
of bromine and calcium hydrate.
The bromine attacks the surface,
and with the iodide forms silver
bromo- -iodide. When the surface
assumes a steel-gray or violet color
the plate is removed and once more
placed in the iodide box for third
of the time originally necessary. In
this state the plate Is exceedingly
sensitive and is ready for exposure
in the camera.
Development in Mercury.
after exposure, the development
is accomplished by exposing the i'm
pressed surface to the vapor Of
mercury. A cast-iron tray, with
wooden sides and lid, is convenient.
At the bottom is placed thin layer
of I mercury, the temperature Of
which is raised to about $50 degrees
F. The plate is placed In the box,
face downward, on supports, and
the development is allowed to pro-
ceed, the process being watched as
it progresses by inspecting 1t from
time to time in a nonactinic light
If the exposure be right the image
will be brilliant; If underexposed 1t
will be weak; whilst II overexposed
it will be covered with . veil OF
mercury"