I'm a long way from last using either dev, but from my early experiences
I would have expected bromide or chloride to have acted as mild solvent
agents with a restraining and buffering side-effect, with slightly more
activity from bromide.

Perceptol, which I used for a long time both straight and diluted,
generally had a far superior resistance to aerial oxidation, and with
the long dev times involved for 1+3 user (an extreme) with inversion
agitation, that was technically better. Microdol-X generally proved
slightly harder to dissolve, with more tendency to leaving a small
residue needing filtering, and oxidised more rapidly in stock solution
or diluted working solution.

Kodak used the 'X' suffix to indicate films or processes which were in
line with sensitivity revisions - originally, the X was used to indicate
filmspeeds only. X indicated a speed approximately 32 ISO (pre-war), XX
64, XXX 125. With the changes in calculaton of filmspeeds using density
above fog threshold in the 1950s, X became 64, XX 125 and XXX 250;
further improvements in emulsions meant that Tri-X (XXX) increased to
320 - the rating which still applied to Tri-X Professional into the
1980s - and then 400 for general stock. Panatomic-X remained peculiarly
stuck in the past and was only 32 ASA (ISO) and eventually the whole
concept just got muddled so that no-one really remembers why Tri-X is
called Tri-X! Plus-X, or course, was a little bit faster than X in the
final stages where X meant 100, XX 200 and XXX 400.

Whatever formulation changes were present, the X in Microdol-X probably
got there as part of a marketing concept, and indicated the suitability
of the developer for use with these films - but also implied a retention
of filmspeed. Though Microdol-X (like Perceptol) incurs a loss of around
1/3 to 1/2 the conventionally measured filmspeed unless diluted, it was
in its day far superior to strong solvent developers, which lost half to
 2/3rds of available speed and also produced a very low acutance by
destroying micro-contrast. But strong solvent developers were not averse
to using sodium thiosulphate in the dev, being half way to a monobath.

So the X probably just marked the spot... signalled that this was a
fitting companion dev to Panatomic-X, Plus-X and the 'generation X' of
films with their revised sensitivities.

For anyone keen on experiment, in the 1970s I made an ad-hoc special
effect developer by mixing a chromium intensifier bleach with a print
strength MQ developer - in much the same way as a monobath. Negatives
developed in this produce a direct posterization, with a distinct set of
steps, but you have to start the development in a regular developer then
transfer to the combined intensifier/redeveloper mix for the second half
of the dev time.

David
http://www.freelancephotographer.co.uk/
http://www.maxwellplace.demon.co.uk/pandemonium/

Thanks for the explanation, but I still find it intriguing how a
developer works with such a hig ammount of restrainer in it!

Jorge

"Richard Knoppow" <dickburk@ix.netcom.com> wrote in news:VGUuc.18900
$be.17095@newsread2.news.pas.earthlink.net:

  Have a look at the MSDS. Perceptol contains a very large
amount of bromide. I think the bromide in Perceptol and
chloride in Microdol-X have about the same effect. They slow
down the development. Neither is a halide solvent. There is
considerable solvent action in both developers due to the
high concentration of sulfite and long time of development.
However, the effect of sulfite as a solvent is very often
mis-understood. Sulfite has no significant action on the
developed silver. Nor does it etch the corners off silver
crystals. Rather, it removes a layer from the surface of the
halide crystals and changes the shape of the developed
metallic silver crystals. A small amount of solvent action,
about what is found in D-76, causes an increase in film
speed by exposing more development centers to the developer.
More action, as in Microdol-X, Perceptol, or D-25 when they
are used at full strength can dissolve some of the
development centers, or in other words, destroy some of the
latent image, causing a loss of some speed. When diluted
this effect does not take place. Note that the developing
times for these developers is quite long in comparison to
developers without an extra-fine-grain property. This is the
result of the very low activity of all three. The same thing
is found in the old Para Phenylenediamine developers. PPD is
very low in activity, about the lowest of any practical
developing agent, and it is a halide solvent. A pure PPD
developer may take more than half an hour to develope even
modern film and will lose four or five stops. It does have
finer grain than any other developer but the great speed
loss and generally very low contrast made it impractical.
Most of the practical PPD developers combined it with
something else, often Glycin or Metol. These developers had
no advantage over developers like D-25, Microdol-X, or
Perceptol so fell out of use.
  Grant Haise discusses extra-fine-grain developers a
little in his book _Modern Photographic Processing_. This
book, which was long out of print, is available in an
excellent reprint from the author.

"Keith Tapscott."
<Keith.Tapscott..1m23ny@news.photobanter.com> wrote in
message
news:1111093563.4a84a3e7cd7a5ab5b32db02f48e659d4@teranews...

  Well, well, very interesting. I was sure I had an older
MSDS for Perceptol showing the above but the later MSDS
showed Potassium or sodium bromide rather than chloride.
That puzzled me. Chloride is a known fine grain agent. I
wondered if there was perhaps an error. I will check the
Ilford site later. If its sodium chloride then Perceptol and
Microdol-X are virtually identical, which is what I used to
think.
  The Edgar Hyman formula was published and is mentioned by
Grant Haist in _Modern Photographic Processing_. I think
there may also be a patent for the formula or something near
it.
  Sodium tripolyphosphate is a sequestering agent for
mineral salts in the water as is Calgon. Calgon is also a
good alkali for developers. Boric anhydride becomes Boric
acid in solution probably used to adjust the pH and act as a
buffer.
  Constituents present in very small amounts may not have
to be shown on an MSDS, especially if they are not
considered hazardous. Microdol-X is supposed to have a
silver sequestering agent, perhaps a mercaptan, to prevent
dichroic fog and excessive physical development from the
dissolved silver halide. This is the difference between the
original and the X version. My guess is that Perceptol has
something similar in it for the same reason.
  Either of these developers, when used full strength, on a
film like 100T-Max, Delta 100, or Fuji Acros, will produce
negatives rivaling Kodak Technical Pan for fine grain but
with considerable more speed (around ISO-50) and no trouble
from excessive contrast.

"Keith Tapscott."
<Keith.Tapscott..1m23ny@news.photobanter.com> wrote in
message
news:1111093563.4a84a3e7cd7a5ab5b32db02f48e659d4@teranews...

  On checking my files I find I have the current MSDS and
it does list Sodium Chloride. I strongly suspect the MSDS
Ilford has had on the web for the last several years,
listing a large amount of sodium bromide, was in error. The
current MSDS indicates Perceptol and Microdol-X are either
identical or close enough to make no difference.
  BTW, the MSDS for "part 1", which has the Metol in it,
describes it as "brown powder". Evidently, Ilford expects
some oxidation of the Metol. Metol, when fresh is white or
very light gray. It can oxidize very quickly in the absense
of a protective agent. For instance, the normal color of
Dektol when fresh mixed is light straw yellow. Using water
that has been boiled and allowed to sit and cool will
minimise this because the boiling removes much of the
dissolved gasses. Metol will not dissolve in a concentrated
solution of sulfite, which is why it is dissolved first in
developer formulas, but adding about 5 grams of sulfite per
liter of water will not interfere with its solution and will
absorb some of the free oxygen in the water.