Clarifying sulfur and sulfur + gold treatment

Nodda Duma

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Ok I'm tracking. It makes sense... Sounds like what I plan but you described it more eloquently.

Thanks,
Jason
 

Nodda Duma

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Well, more eloquent than my Southern redneck jibber-jabber. It’s all relative.
 

Nodda Duma

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Haha fair enough. Please give her my regards.

I did some testing last night (finished at 2am!) and found best sensitivity somewhere around 60 mg Hypo / mol silver. You have given in your book an empirical relationship between amount of sensitizer and grain size? Is it valid to say "My emulsion responds best to ~ 60 mg / mol, so I can infer my grain size distribution is centered around X um?"

I have sufficient data to plot density vs. amount of hypo (between 5 mg/mol and 100 mg/mol) added, and can see the sensitivity increase, reach a peak at some value near 60, and then decrease again. Of course, I'm an old hand at data analysis, so I can theoretically perform a curve fit (assuming 2nd order is sufficient) to predict what the optimal value should be. Fog almost seems to increase in parabolic fashion after a certain amount is added beyond what is optimal.
 
OP
OP

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Well, you can say that your average grain size is centered around X microns. TAI can repress fog and extend finish result to get more speed and adding gold does even more. There are other addenda that can push this even more. Addition of Iodide can increase speed although by a different mechanism. It is still a surface effect however.

PE
 

Nodda Duma

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As they are both surface effects, I would expect the sensitization of Iodide with Sulfur would not be additive. Is that correct? So for example, Sulfur alone might add 3 stops and Iodide alone might add 2 stops, but adding both wouldn't necessarily see a 5 stop increase in speed.... the combination might only provide 3 1/2 stops or something (numbers kind of made up).

Gold and sulfur seemed to work the same way as well.
 

ludwik

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I know its an old topic.

Photo engineer mentioned blotter test for fog every 10 minutes, stop when fog is noticed.
I'm new to this stuff (just do basic emulsion for now).
and this maybe a stupid question - how the fog look like?
 

ThePhotoChemist

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ludwik said:
I know its an old topic.

Photo engineer mentioned blotter test for fog every 10 minutes, stop when fog is noticed.
I'm new to this stuff (just do basic emulsion for now).
and this maybe a stupid question - how the fog look like?
Click to expand...

Not the best example, but it'll look something like this:


I usually do a sample a T=0, and then 10 minute intervals after that. You can see the samples start to darken the 30 or 40 minute mark.
I tend to take samples on a piece of glass, and let it dry completely. Then (still under safelights) pop it into a developer (D-19 here but anything works), and see which samples start to darken without having been exposed to light.
 

koraks

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ThePhotoChemist said:
Then (still under safelights) pop it into a developer (D-19 here but anything works), and see which samples start to darken without having been exposed to light.
Click to expand...

Just checking, and out of curiosity: this particular set of strips, did you develop them but no fix? The pink hue suggests silver halide that's in the process of printing out, hence the question. If you didn't fix this - why not? Wouldn't it be more reliable to also fix and then determine the density of the fog by e.g. putting the glass plate on a white surface?
 

ThePhotoChemist

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The pink hue here is from the erythrosine, since all my emulsions are panchromatic, and it tends to work better when added before precipitation.

As far as fixing - you're correct, this is not fixed, just thoroughly washed. I fixed the very first one I made, but the fog here is pretty subtle, and fixing it makes it pretty hard to spot when it starts occurring. Really I just need a few seconds in the light to determine when the fog starts, and maybe snag a quick picture for reference before it starts to print out, before I wipe the plate clean anyway.
 

ThePhotoChemist

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ludwik said:
How do you know that enough is enough? on your sample last strip is the one when you stopped?
Click to expand...

So basically here, your goal is to add gold/sulfur in a certain amount, and then apply heat until it starts to fog. As soon as your fog starts, you know that's the amount of time you can apply heat to get your maximum speed increase before you start creating a base level of fog. But the problem is, you don't really know when the fog starts as you're heating it (especially since it takes forever for the gelatin to dry).

So here, I'm taking a sacrificial sub-batch (usually 50mL out of a full batch of 350mL), and apply the same proportion of gold/sulfur. Then I take samples at 10 minute intervals for 1 hour. Unlike the picture I showed earlier, quite often the last sample taken has turned completely black, and the sub-batch is unusable. But it should still give you the information you need to see when the fog starts to show up -- so if it starts to darken at the 40 minute mark, you know that when you sensitize the rest of your batch, to cut heat at 30 minutes.

In theory, if you're making your batches consistently, you can use this for future batches too. But for me, they're a bit all over the place, so I do this test every time. Sometimes they come out like the picture I posted, where the fog is pretty subtle even at the 60 minute mark. Sometimes it'll go completely black at the 10 minute mark, and I'll halve the amounts of gold/sulfur and back the heat down and try again with another sub-batch.
 

ludwik

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As I read about all of it then amounts of every thing depends on mole, grain sizes etc. too many variables. Is there a simple formula I could follow? (like for 400ml of emulsion use x grams of thiosulfate) so maybe it wont be perfect but will jump emulsion from basic ISO 2 to maybe ISO 10? 20? I would be more than happy about that. (maybe what I say makes no sense or is just plain stupid... I'm on my first steps and want to make emulsion just because there is nothing like that available commercially and I just want to use all those old beautiful cameras I have).
So maybe someone could share a good formula recipe that I could just follow step by step.
Thank you
 

Sparks n Fire

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erythrosine imparts orthochromatic sensitivity, what dye are you using to make it panchromatic?
 
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