Increasing Azo Contrast

[David Hall]

For those of use who use Azo in Amidol, we know that using a water bath will decrease contrast up to a whole grade.

But what if I need to increase it? The highest grade paper I have is 3, and I have a negative that is still flat on that. Is there an exposure or chemical way to take the grade 3 paper toward 4? Using Amidol?

dgh

[Jorge]

David, I have never tried this and dont know if it will work, but if you can decrease contrast by "bleaching" the latent image with ferrycyanide before you develop, perhaps you can increase it by "toning" the latent image before you develop. Why dont you try selenium toner maybe 1:500 and put the print in the bath before you develop it. Rinse it and then develop it in amidol, and see what happens, and let me know if it worked.

[Donald Miller]

David,

If what Jorge suggested does not work (it may very well do so), the things that I would try would be:

1.intensify your negative with selenium toner. Since selenium is proportional to silver density it will increase negative contrast. I have used selenium in dilutions of 1 to 3 for this purpose.

2. If that doesn't produce enough contrast the next step would be to create a low density unsharp negative mask of your camera negative. This mask would be printed along with your camera negative. The mask will give you an unlimited amount of contrast increase depending on the density of the mask.

Good luck.
Donald Miller

[David A. Goldfarb]

In general I find I need one zone more contrast with Azo than I do with most grade 2 enlarging papers.

Selenium intensification of the neg will give you about a one-zone boost. I'd try that first. I also use 1:3 for this purpose.

Another thing you might try is printing down the whole image then bleaching it back to the highlight values you're after.

[David Hall]

Donald and David,

I have always been interested in intensifying a negative but never did it because I don't understand the chemistry of it enough...if I intensify it by one full stop, do I either blow highlights or erase shadow detail in the process?

dgh

[David A. Goldfarb]

Selenium intensification adds density proportionally to the negative. If the negative is flat and you want up to one zone of expansion, you won't blow the highlights, but you will bring them up one zone. If the negative already has sufficient contrast, then you would blow the highlights by bringing them up one zone, but why would you intensify a negative that is already sufficiently intense? You won't lose shadow detail at all. Rather, you'll increase it.

[David Hall]

Great. I will try the intensification tonight. Anything I need to know other than selenium 1:3? Do I need to constantly agitate to avoid streaking or blotching? Is it easy to see it happening, or do I measure it by time?

dgh

[David A. Goldfarb]

I would agitate constantly in a tray, but I've never had streaking problems. You can see it happening if you use a white tray and have good light, but for reference, I usually go about 8 minutes in Kodak RST 1:3, 68 deg. for thoroughly washed negs (re-wet them first, if they are dry) that have been fixed in an acid fixer. I haven't timed it precisely for negs fixed in TF-4, but it's probably shorter.

[Donald Miller]

David,

I don't think that you can leave a negative in the selenium too long, within reason. It will reach a point of maximum effect and nothing happens after that. The selenium actually would have the same effect on the silver density of the negative that it does on paper. It would tend to make the negative image more archival since the same chemical change occurs.

[David Hall]

Thanks!

And, Donald, to answer your signature line...

"whoosh. Whoosh. Whoosh."

dgh