This is irrelevant. The specie that is involved is bromide, not bromine, and bromide does not react with developer oxidation product. The restraining mechanism of bromide is well understood in terms of electrochemistry but this has nothing to do with the interaction suggested above.
Originally Posted by Jorge
It is true that the action of bromide on chloride emulsion is different (a different mechanism kicks in). But my guess is that Sandy used a camera negative emulsion and this is probably not the case.
This is not really the case. It really depends on the aim of the developer design. Benzotriazole, or preferrably more strongly adsorbing antifoggants may be necessary in color developers, but they are not necessary in phenidone developers. (of course, they can be used for certain ends, but not generally necessary.)
Originally Posted by Gerald Koch
The reason some develoeprs (like color developers) require strongly adsorbing organic antifoggants is because the developing agents have stronger adsorption to AgX crystals and this is a competition for adsorption. Phenidone has stronger adsorption than Metol in regular developer conditions but nothing like color developing agents.
Interestingly, neither the C41 nor RA color developers use an organic antifoggant. The C41 developer relies on a Br/I mixture and the RA developer relies on a Cl/Br mixture for antifogging.
Organic antifoggants used in color developers adsorb so heavily and selectively, they tend to act on a single layer or component in the color material and can therefore be bad rather than good.
The only negative product color developer to rely heavily on an organic antifoggant and selective action on a layer was the CP-100 series of developers used for high temperature drum processes for Ektacolor Professional Paper, T1920 and similar products in the 60s.
Organic antifoggants are used in color negative films as DIR fragments to control interimage and image structure. E6 films are another matter entirely.
Originally Posted by Ryuji
OK, I will be more specific. I did not give a lot of detail in the first message because the results surprised me so much I was just trying to find out if there was anything in the literature that could explain them. If not, I may need to re-think the testing methodology to see if there is an error.
First, the developer. The working developer was mixed from regular Pyrocat Stock A and B solutions, but with no bromide. I mixed one liter for the test, and each liter would contain the following.
sodium metabisulfite -----0.1g
potassium carbonate -----10.0g
The test film was Ilford FP4+. I used 100ml of solution per sheet of 4X5" film, so each sheet was developed in 1/10 of the above amounts. That is, in 100ml of developer there would be the following.
sodium metabisulfite ------ 0.01g
potassium carbonate --------1.0g
Development was in BTZS type tubes with constant agitation. Three sheets of film were developed, in separate tubes but from the common solution, and they were developed together in a water bath. The only difference was in the amount of bromide added to the developer. Sample A contained no KBr, Sample B contained 0.001g of KBr, and Sample C contained 0.002g of KBr.
The sample tests were made by contact printing a Stouffer TP45 step wedge, using a standard light set-up that I dedicate to film testing in which exposure is controlled with a light integrator.
When I read the densities here is what I found
Sample A (no bromide)
Step 21 ----- .14
Step 11 ----- .59
Step 1 ------1.42
Sample B (0.001g of KBr in 100ml developer)
Step 21 ---- .13
Step 11 ---- .63
Step 1 ------1.54
Sample C (0.002g of KBr in 100ml of developer)
Step 21 ----.12
Step 11 ----.59
Step 1 -----1.45
I did this test three times and got similar results each time. The B+F values are higher than what I expect with FP4+ sheet film, but this particular film is several years old and has developed about log 0.6 of film base fog. I could easily do the same tests with other film but before I waste my time doing that I wanted to post the results to see if anyone could find an obvious flaw in the methodology of the testing itself.
Last edited by sanking; 09-10-2005 at 11:11 AM. Click to view previous post history.
Sandy, I have no very confident explanation for this, but my suspicion goes to the use of fogged film. Fogged grains (due to emulsion aging at improper condition, etc.) are rather different from emulsion uniformly exposed to weak light exposure. Fogs often develop in smaller grains while light exposure would render larger/sensitive grains developable. Small grains have greater surface area to volume and they are great adsorption sites, and if they are developable, they may consume a significant amount of developing agents. But bromide might have worked preferrentially against fog development at certain concentration.
Another concern is the use of relatively small amount of developer for testing like this. I know BTZS tubes users usually use small amount of developers and continuous agitation, but when you are testing developers, the developer performance should really be tested in large baths first, and then determine how low the volume can be cut down without noticing the difference. Otherwise, when you get some idiosyncratic results particualr to some film or exposure, you may be trying to make a dangerous generalization without knowing. You could still use BTZS tube if you could cut the films in 1/4 and use smaller step tablet, for example.
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So, you don't trust the Russians? Or you think I made it up. Oh, well.
Sandy, what is interesting to me is that in your three sets of density figures above, not only is there a difference in the fog level, but a significant difference at higher densities. I use Pyrocat-HD without bromide (roll film, for VC paper), my reasoning being that reducing the restraining effect would perhaps give me a smidgen more speed with an insignificant increase in fog. But maybe I'm actually "back at square one" and it's effectively the same as standard pyrocat-HD. Strange.
Well, I ran the same test this afternoon with TMAX-400 and got slightly different results. The results were more linear as I had expected from the FP4+ film. Here are the densitometer readings for Visual, Blue and UV light. I did the test twice with very similar results. Here is data from one of the sets.
Originally Posted by john_s
Visual-----(A) No KBr ---(B) 0.005g Kbr/liter---(C) 0.02 g KBr/liter
Step 11------- .67--------------.66----------------------.61
Blue-----(A) No KBr ---(B) 0.005g Kbr/liter---(C) 0.02 g KBr/liter
Step 11------- .79--------------.77----------------------.72
UV------(A) No KBr ---(B) 0.005g Kbr/liter---(C) 0.02 g KBr/liter
People can conclude what they will from the data, but what I conclude is that if you are printing with TMAX-400 negatives on silver papers, both graded and VC, the formula is optimum with no KBr at all. However, if you are printing with both silver and UV sensitive processes the best compromise appears to be adding about 0.005g - 0.01g KBr/liter of working. This can be achieved by reducing the amount of bromide in the Stock A solution from the present 2.0 grams per liter to 0.5g - 1.0g per liter.
Irrespective of the reason for the non-linear anomaly in the FP4+ tests, all of the data suggests that the formula is slighly optimized with the reduction of KBr in a liter of Stock A from 2.0 grams to 0.5g - 1.0g.
Last edited by sanking; 09-10-2005 at 09:40 PM. Click to view previous post history.
Sandy - I would like to suggest that when measuring differences of 0.01 density, you are probably not likely to get any significance to any one measurement by simply making one measurement.
Your densitometer is probably repeatable to +/- 0.01 OD at that density level. And then there will be differences in the manufacture of the films you are testing, even though I suspect you are trying to minimize that by using sheets from the same production lot number or even the same box.
One way to try and get more precise readings when you have measurements that differ by this little is try to read each Step several times. If your densitometer has a sensor size that has a diameter of 2 or 3 mm, make several measurements across the length of the step. Space the readings apart by a distance that is a millimeter or so larger than the diameter of your sensor diameter. Then average the readings. While you are at it, figure out the standard deviation.
If you really want to minimize things, read a spot on one film, then the next film, and then the third. Then move to the second spot on the first film and repeat the process until you get across the Step on all 3 films. This will hopefully eliminate any variation in reading based on time from your densitometer. Drawing a grid on to the Step can help with this.
Were they using polywater to dissolve their chemicals? See http://www.cs.cmu.edu/~dst/ATG/polywater.html
Originally Posted by gainer
Anyway - I've always enjoyed this exchange from Dr. Strangelove:
General "Buck" Turgidson: A-A-Am I to understand that the *Russian* ambassador is to be admitted entrance to th-the War Room?
President Merkin Muffley: That is correct, he is here on my orders.
General "Buck" Turgidson: I... I don't know exactly how to put this, sir, but are you aware of what a serious breach of security that would be? I mean, he'll see everything, he'll... he'll see the Big Board!