Originally Posted by Simon R Galley
Since I don't know your formulation, I cannot comment with authority. Lets just say that Ilford MGIV darkens rapidly when light fogged then treated with an alkaline solution. Kodak paper does darken even more so than Ilford paper. Many other papers do not. For example, the Kentmere papers I have all fail to test positive.
So, there appears to be a reducing agent there somehow that is forming silver. The intention may not be for development, but it does test positive. The test, of course, detects any reducing agent which acts on silver halide, and which is also the generic and broad definition of a developing agent.
I've been pacing the floor here trying to figure this one out.
It is probably the case where an addendum in the paper, added there for one reason or another, can give a false positive with the fogged paper + alkali treatment test. That is the only explanation for the results.
So, I would like to warn you that this test can give false positives. AFAIK, it cannot give false negative tests as long as you use strong alkali.
Here is an interesting test. I coated some of my Azo emulsion which I know has no developing agent or reducing agent in it. I then took 3 pieces of paper, namely:
1. Kodak PCIV
2. Ilford MGIV
3. My 'azo' work alike.
In the light I placed about 5 drops of 4% Sodium Hydroxide on each.
Results: Kodak paper blackened instantly, Ilford paper blackened slowly and the droplets took on a visible orange or lemon color. The paper I coated did not change.
Now is the interesting part.
I held the Ilford paper over my paper and let the orangish drops of Sodium Hydroxide run off onto my paper from the Ilford paper. My paper instantly began to blacken.
So, this looks like strong evidence for a 'developing' agent in Ilford paper and it is so strong a reducing agent that it can cross develop other sheets. IMHO this represents a difficult case for processing mixed batches of paper then, if there can be crosstalk between paper types.
So, I know I am not going crazy!
And despite some previous posts here.....
Kentmere and Arista II (same, of course) actually state that they have a DI, although the statements are a bit cryptic.
"Coated Emulsion Layer:
The light-sensitive silver halide emulsion layer has a silver content of approximately 1.5 g/m2 . This is covered with a gelatine supercoat which protects the emulsion from stress fogging and physical damage, as well as containing a developing agent. (Machine processable but can not be used in activator/stabilization processors.)"
Kentmere says the same thing.
So, yes, Virginia, there definitely are DI papers still out there.......
You and I have pointed out that some papers
Originally Posted by Paul Verizzo
have DI supercoats. Freestyle states that their
Arista EDU.Ultra has a DI emulsion. With that
it is still not activator developable.
The issue is more complex. As PE has alluded,
there may be substances, 'reducing agents', which
might be considered developing agents under certain
circumstances. These suspects may or may not interact
with the processing chemistry.
I believe that Simon is correct in a real world context.
Also Freestyle, who a few years ago assured me that
NONE of their Graded papers have DI emulsions.
I've tested at least a half dozen emulsions and not
found by a straight carbonate test any to show even
a trace of development.
In the Freestyle example the purpose of the
DI emulsion in that one Graded paper is to speed
the students along. As for DI papers; activator
process, no developer needed.
As for myself, I do test; expose then develop in
a weak sodium carbonate solution. Beyond that
the matter is purely academic. Dan
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I think you hit the nail on the head, here.
Originally Posted by dancqu
The original intent of my post was to avoid having a developer in the emulsion interfere with my chosen developer intentions.
It looks like it just won't happen.
I'm not so sure it won't interfere. It is said that older papers were more amenable to developer controls and to toning than many modern papers, and the presence of reducing agents in the emulsion may be partly responsible for that. Another factor is probably the pre-hardening of modern emulsions.
David, you are right. Modern papers are formulated in a much different way than the older papers and one thing in particular is true. You cannot easily 'push' a modern paper. They basically stop development when done. Older papers continued to gain contrast and speed and fog. That isn't to say that modern papers do not, just that they 'resist' change beyond a certain point.