Developing Micrographs
Subjects for micrographs, whether optical or electron, can often show greater
contrast the the usual subjects of snapshots. Here are a few procedures
which may be useful in such cases.
This is a useful developer for black-and-white films, taken from Modern
Photographic Processing by Grant Haist. It is a recipe from the 1930s,
by Willi Beutler.
Solution A: 5g Metol plus 25g Sodium Sulfite Anhydrous in 500ml Water;
Solution B: 25g Sodium Carbonate Anhydrous in 500ml Water.
Keep solutions separate until ready for use. Mix 30 ml A, 30 ml B, 300
ml water at roughly 22^C;
Develop for 8 min, inverting thoroughly once every minute;
Throw away developer, wash with water at roughly the same temperature,
and fix.
This is a very robust developer, giving reliable results with good
definition as a result of its acutance properties. It can also be
used as a compensating developer to give definition in both highlights
and shadows as follows:
Over-expose your film for highlights by about 8 times;
Soak in 100 ml A, 200 ml water for 8 min.;
Pour away the A, and replace with 30 ml B, 300 ml water;
Throw away solution, wash with water at roughly the same temperature, and
fix.
Note that Solution A has a limited shelf life, perhaps a couple
of months. Once it has gone dark brown it should be discarded. However,
the robust nature of this developer (being relatively insensitive to small
variations in time, concentration and temperature) make it ideal for the
hit-and-miss work of research subjects.
I have found that microscopic subjects tend to need more attention to
shadow detail, and that highlights tend to be over-emphasized by conventional
Metol-Hydroquinone developers. The formula above, being Metol only, helps
out the shadows and does not overcook the highlights. I always use AnalaR
Metol, because impure Metol contains more toxic impurities (I also wear
rubber gloves). Because some people are sensitive to Metol toxicity, these
days in commercial developers Metol is being replaced by phenidone; however
when formulating with this much smaller quantities and accurate weighing
are needed.
For printing
A similar compensation technique using ordinary paper developer can be
used for prints from negatives with a wide range of contrasts.
Expose your paper sufficiently for the shadows;
Develop under safelight until the image just starts to appear;
Immediately whack face down on a tray of water, to allow the image to develop
in the residual solution trapped in the paper;
If necessary, soak the paper for up to a minute to take up some more developer,
then repeat the previous step;
When developed enough, fix.
Film Recommendation for Optical Microscopy
For black-and-white, I find Kodax TMAX 100 the best yet for optical microscopy.
It allows a large latitude in light levels, and so this means that when
using polarized light one can simutaneously photograph objects near extinction
and those showing large birefringence. And the quality of the developed
negative is very good - "brilliant grey", if such a colour exists.
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Boiling strong acids
We have slightly revised our procedure regarding the preparation of dry
phosphoric acid for the "2:1 dry" etchant. We now find it better to heat
the 85% phosphoric acid in a conical flask standing on a hotplate (it is
good to use a Quickfit conical with a simple condenser to take off the
water if you like). Heating in a round bottomed flask in an isomantle is
LESS safe. It is not generally known, that isomantles are MORE dangerous
in regard to bumping, because of the uniform gentle heat which allows the
whole liquid volume to superheat. The conical on a hot plate develops localized
hot spots which nucleate boiling before the whole mass of liquid gets too
hot: a Bunsen burner on a gauze is even more effective in this regard,
and in skilled hands is even more controllable (this controllability featured
in a British "High Speed Gas" advertisement). Because phosphoric acid is
not organic there is no danger of fire.
However, to prevent bumping you still need some sort of anti-bumping
granule - with phosphoric acid you cannot use the ordinary alumina granules,
and smashed up ceramic crucibles don't work. The thing that DOES work is
PTFE, and a PTFE-covered magnetic stirrer bar is ideal for the purpose.
You don't need to stir it, so an ordinary powerful hotplate will do.
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