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Photo Engineer
09-04-2008, 11:46 AM
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. :D

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.

PE

JOSarff
09-04-2008, 11:47 AM
And I will try a gold chloride sensitizer(Stiegmann's?), after I haved looked at it without one.


Bill:

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.

PE

He also attached two jpg's with some good info.

Hope this helps.

Joe

wildbillbugman
09-04-2008, 12:15 PM
Thanks Joe,
Now that you mention it, I do recall that post(s) by Ron.
Kirk,
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.
Bill

dyetransfer
09-04-2008, 12:31 PM
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

Photo Engineer
09-04-2008, 01:45 PM
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.

PE

Photo Engineer
09-04-2008, 01:47 PM
Joe;

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.

PE

Kirk Keyes
09-04-2008, 02:51 PM
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. :D

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.

PE

OK - I remember that. But maybe it was after I fell out of the chair. And I was not sleeping!

Ray Rogers
09-04-2008, 03:02 PM
my crystals in the second attachment...
Joe

Ron, It is 4 something here- I just woke up...

Are the crystals in the second jpg ones you actually precippitated for these experiments, or is the photograph just taken from a similar emulsion?

Ray

Photo Engineer
09-04-2008, 03:05 PM
Kirk;

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? :D

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.

PE

Photo Engineer
09-04-2008, 03:05 PM
Ron, It is 4 something here- I just woke up...

Are the crystals in the second jpg ones you actually precippitated for these experiments, or is the photograph just taken from a similar emulsion?

Ray

That is one of my emulsions Ray.

PE

Kirk Keyes
09-04-2008, 03:25 PM
Now for finishing, you are using thiocyanate + gold. Here is the order of use timewise from early days to modern:

Active gelatins > Allyl Thiourea > Thiourea > Thiocyanate > Sodium Thiosulfate

Gold was used after about 1945 at Kodak with all of the above, but hypo was used exclusively for Sulfur sensitization since the 50s or 60s.

Ron-- since you're discussing sulfur+gold again, I was wondering why there was such a progression in the use of sulfur compounds over the years. Any ideas as to why thiosulfate was not used from the beginning?

Sheppard in his patent (#1623499) mentions that "sodium hyposulfite" can be used, but then immediately says that this compound is in name correct in the scientific sense and not the compound with the same name used by photographers which is sodium thiosulfate...

By hyposulfite, if he means salts in the archaic system where it's sulfite (SO3=) but with one less oxygen (making SO2=), then (As taken from wikipedia): "However salts containing SO2= and the corresponding acid, hyposulfurous acid (H2SO2) are not believed to exist." - then what would he have been referring to?

OK - I guess I can see it in my 1932 CRC Handbook - it has NaHSO2 and calls is sodium hyposulfite. But I think this is what is called sodium dithionite - not to be confused with sodium dithionate, Na2S206.

So why did he miss thiosulfate in the original patent. He sure listed a lot of other compounds, it seems like thiosulfate would have been something to try, and something they had at hand, too.

Photo Engineer
09-04-2008, 03:47 PM
Kirk;

Since the discovery of sulfur sensitization hinged on discovery that a thiourea was causing it, there was a natural progression in use of heat degradable sulfur compounds. That is my only guess here. IDK why. I do know that formulas from the 40s and 50s used Thiocyanates and then moved to Hypo. Early ones used Thioureas.

I do know (I think, in the back of my memory) that the Thiourea sensitizations were hard to control, and that there was something specific about sulfur + gold where hypo was used. That is it, just a hint of memory.

PE

Ray Rogers
09-04-2008, 04:50 PM
Ach hum!

Ron, Kirk;

You guys must be sleepier than I am.
Somebody missed hypo, but it wasn't Sheppard!

Ray

Photo Engineer
09-04-2008, 05:07 PM
Well, Agfa used Thiocyanate salts for quite a while but Kodak was converting to Hypo IIRC. IDK the precise timeline.

PE

Kirk Keyes
09-04-2008, 06:45 PM
Somebody missed hypo, but it wasn't Sheppard!


Is it in his first patent? If so, please point it out and then I'll agree with you that it was I that missed it.

Ray Rogers
09-04-2008, 07:03 PM
Is it in his first patent? If so, please point it out and then I'll agree with you that it was I that missed it.

It was in the patent you quoted, with his notes about hypo.

Ray Rogers
09-04-2008, 07:41 PM
It was in the patent you quoted, with his notes about hypo.

To suggest Sheppard missed hypo verges on being sacrilegious!

However, the position attained latter on by hypo certainly is not reflected in the early published reports, and initally there was some confusion, and a different allocation of emphasis was given. As Kodak did the leg work, their understanding changed.

(PM me if you can't find it)

Kirk Keyes
09-04-2008, 09:46 PM
OK Ray - I see that I had not found an earlier patent. Thanks for pointing that out...

1574994 (1926) DOES mention the use of thiosulfate as a sensitizer, but 1623499 (1627), the one I quited above, DOES NOT mention thiosulfate. And Sheppard goes on to make sure you know that he's not talking about thiosulfate as well.

So why the difference in the two patents then?

Kirk Keyes
09-04-2008, 09:47 PM
OK So why the difference in the two patents then?

Ray - you seem to quote yourself in sequential posts. What's up with that. It confuses me to see you having a conversation with yourself...

Kirk Keyes
09-04-2008, 09:49 PM
It was in the patent you quoted, with his notes about hypo.

I still missed in in the one I quoted I guess. And my buddy Google Patents doesn't find it when I search on thiosulfate either. Granted, google doesn'thave the best OCR.

Can you please give me page and line number...