Low pAg emulsions

[diant]

Lippmann/holographic emulsions might be an other area...

Of course. Excuse me, I'm forget completely...

[Hexavalent]

By the way, if we speak of Red-sensitization, It is generally accepted to state 1950 year as year of its discovery (pioneer work by Lowe, Jones, Roberts).

1950? Red sensitive materials were discovered and in general production long before 1950.

[Photo Engineer]

I have been reading some of my text books to learn more about Ag excess. We never worked with them in my time at EK As Far As I Know (AFAIK).

Sulfite was also used as a preservative.

PE

[diant]

> Sulfite was also used as a preservative.
It is Red-sensitizer too. Again Burt was the inventor of this role of sulfite (B.H.Carroll, D.Hubbard: The Photographic Emulsion: Sensitization by Sodium Sulphite, 1933).

Ron, 3 hours ago I synthesized new Ag-excess emulsion and poured it on glass plates. This time I washed it by acid water (pH = 2,1) and tomorrow shall test it in shooting and developing.

To Hexavalent:
In this case "Red-sensitization" is not spectral sensitization at all but shortening of "Reduction Sensitization" (excise me for unhappy contraction). I mean the chemical sensitization ("after-ripening" in term of english reseachers).
Reduction Sensitization was the main companion of Sulfur Sensitization before 1930-s (when Koslovsky from Agfa discovered Gold Sensitization) - that was the time of active gelatins.

[Photo Engineer]

Yes, spelling out the "reduction" would help some.

I have been looking up "R" typing in my notes. Stannous Chloride has been mentioned. It can cause fog.

PE

[diant]

Yea, temporary abandon...

My yesterday's shooting was commencing with the great news - fog was overcame.
Finish emulsion (before coating) had pH=2,7. After one day storage I hadn't any fog after 5 min developing in metol-hydroquinone mixture at 23 degree (Density of fog+glass was 0,08).

I was preparing to celebrate the victory... But the very first snap showed that something was wrong.
I'll not enter in all detail, but only short sum.

1. Strong acid emulsion has ve-e-e-ry weak adhesion to the glass. After developing and fixing I had emulsion floating at one corner and glass resting at its corner... Such acid emulsions need strict tunned sub-layer.

2. Strong acid emulsion quick damages basic developer (and almost every developer is basic).

3. Developing is strongly impeded by acid reaction of emulsion. And what is more strange - I had 20 sec "induction" time when with all my past Ag-excess emulsions I observed only immediate developing. The whole 20 sec! It pushed me to deep thinking and ... next

4. The most bad news is ... I most likely hadn't Ag-excess at all. How it could turned out if I put Ag in excess to bromine. The answer is probably consist in acid washing (I don't see any other possibility). I acidified water by H2SO4. But as I've learned recently Ag is build the non-dissociated complexes with ion SO4- (AgSO4- etc.) But these complexes have good solubility. I indeed washed out in this way all my silver excess which I had on surface of microcrystals AgHal.

Yea, I am setting (at least for time) abandon. And I see now only one really working possibility of shooting with Ag-excess gelatin glass plate - It is bathing of normal Br-excess plate before shooting in silver-ammoniac solution (well described elsewhere).