Chemical sensitization (finishing) emulsions

[Athiril]

I read somewhere that gold was usually only for high speed emulsions and for the purposes of high intensity reciprocity correction?

[Photo Engineer]

There are several uses, but generally Br/I is sensitized with Au/S and Cl and Cl/Br are sensitized with S only. This is a broad generalization.

Au tends to make Cl emulsions have very soft toes and high fog. Treatments patented by several workers devised methods of using Au/S on Cl and Cl/Br emulsions. That was only in the 70s.

PE

[kb3lms]

Other things that can be done... Adjust pH. Lower pH within reason, using citric acid will increase contrast.

Hi PE,

Now that I think I have solved my coating problems, I am doing some analysis on my current (and only, really) emulsion. I am digging through some old information here in the forums and have a question relating to your comment about pH. As I have mentioned before, this batch, an SRAD loosely made according to Denise's TLF#2 recipe, is slow, low contrast and fogged and the fog seems to be getting worse over time. I attempted to do some sensitizing using sodium thiosulfate, and according to what I read above, clearly used too much. At this point I am getting to the end of the pot and am starting to think about making a new, smaller batch. But I'd like to use the rest of this batch for some experiments. I have between 50 and 75ml left.

Anyway, my question. The last 20ml coating I made, I checked the pH and it read as 7.3. The meter seems to be calibrated OK, so I think that number is good. To try improving contrast, what pH might I want to shoot for? Also, how much effect would pH have on fog level?

-- Jason

[Photo Engineer]

Jason;

The SRAD in my book is tested and true. it works. But, if you make anything else, make sure you wash it well and move the final pH to about 6.5. Then proceed.

If you have problems, PM me.

PE