I discussed the other method in the workshop Kirk. Maybe that was the day you were late, or the day you fell asleep and fell out of your chair.
Basically, the only parameter that is important in an emulsion while finishing, if the emulsion is any good to start with, is the fog level. So, all you have to do is test one drop of emulsion for fog. When it starts to rise, the finish has gone as far as it can! Voila, c'est fini.
Originally Posted by wildbillbugman
I asked about the Steigmann sensitizer in a thread called 'Sulfur and Gold sensitation'. Ron was kind enough to supply some guidelines on sulfur and gold content that is closer to a 3:1 ratio, rather than Steigmann's 8:1
To Quote Ron's reply:
The data below assumes the use of KAuCl4 and Na2S2O3.H2O for sensitization:
The data are stated as gold/sulfur in milligrams / mole of silver
1/3 for 1.0 micron grains
5/15 for 0.5 micron grains
35/100 for 0.1 micron grains
The attached chart shows the relationship to the vAg and the crystal habit that is formed. From this, you can see that my crystals in the second attachment are made at a vAg value between 7.5 and 8. The extreme rounding is due to the ammonia used to digest (grow) the crystals, and if taken much further the crystals would be nearly spherical.
He also attached two jpg's with some good info.
Hope this helps.
There is no such thing as taking too much time, because your soul is in that picture. -Ruth Bernhard
Now that you mention it, I do recall that post(s) by Ron.
In my earlier atempts to make emulsions, I had so much trouble with foging that I developed the habit of using Ron's "1 drop" fog test at every step. Now, whenever I make an emulsion, I am constantly sacrificing 1 drop to the Gods of Fog.
I don't think Fotokemika would have done the sensitization test every time they made an emulsion - once you do the test using this procedure, it would have gone too far, and the emulsion would be fogged and unusable. The idea is to continue sensitizing until you detect some fog, and then the NEXT time you make a batch, sensitize for LESS time so that fogging doesn't occur. This should work as long as you use the same materials, batch size, cooling times, etc. Once you have the proper time/temp/concentration for sensitizing, you just stick with it, and shouldn't have to repeat the test.
Regards - Jim
You can sensitize to the first appearance of fog and then add an inhibitor or stabilzer. That is rather kludgy, but it works. Since you do both in your formula, the approach you were taking was not clear to me. I would have had to do your experiment to clarify it for myself.
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Thanks for posting that again. I would like to remind people that sulfur and sulfur + gold react differently and require a different quantity for a given grain size. Also, that chart does not apply to Thiocyanate. I would have to look up specific examples, if I even had any. We did not use thiocyanate in anything I worked on AFAIK.
For the above example that Joe copied here, it was a Br/I emulsion, made at about pAg of 8 on the chart as you can see by the crystal habit. I used 100 mg/mole of Sodium Thiosulfate.5H2O for a sulfur only finish. You can see the difference.
Last edited by Photo Engineer; 09-04-2008 at 02:50 PM. Click to view previous post history.
Reason: Added more data
OK - I remember that. But maybe it was after I fell out of the chair. And I was not sleeping!
Originally Posted by Photo Engineer
Ron, It is 4 something here- I just woke up...
Originally Posted by JOSarff
Are the crystals in the second jpg ones you actually precippitated for these experiments, or is the photograph just taken from a similar emulsion?
I know that! You were a very diligent and alert assistant, and you can work with me in the DR anytime. But why did you fall out of the chair?
I know, you didn't fall out of a chair. I was joking.
But for the rest of you, the 1 drop test for fog is what you can use commonly to determine the extent of finish using a sample with all of the sulfur + gold. Then you take 30 ml and heat to 60C and take 1 drop every 10 minutes and test only for fog. Take the remainder of the batch and treat the same way.
That is one of my emulsions Ray.
Originally Posted by Ray Rogers