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JOSarff
08-14-2008, 01:25 PM
I recall a posting about sulfur and gold sensitation that PE said should be around 3:1.

On the light farm website they use Steigmann standard aurous ammonium thiocyanate solution (50ml ammonium thyocyanate 1% and 6ml gold chloride solution 1%) which is about 8:1. Is this "strong enough" or a comprimise because of increased fog with increased gold?

It's in the section on glass plate emulsions.

Thanks all
Joe

Photo Engineer
08-14-2008, 02:56 PM
Joe;

The 8:1 is from older work and also uses thiocyanate. These two differences make up for what I said which is based on gold choride and sodium thiosulfate pentahydrate. The ammonium ion also has a fairly substantial effect on the final outcome. This all assumes 100% oxidized gelatin. There are only two sources of this product. One is Kodak and the other is Roussellot. The Formulary sells the Kodak product.

PE

Kirk Keyes
08-14-2008, 03:38 PM
So the Steigmann formula was from the time of active gelatins - it needed less sulfur than what phthalated gelatin of today would need as the active gelatin already had sulfur in it?

One of the books I have, I forget which, has a nice graph showing the speed increase from gold alone and sulfur alone and the two combined. Sulfur alone was more effective than gold alone, but the two combined with much better than either alone.

Photo Engineer
08-14-2008, 03:45 PM
Yes, the Steigman formula was used during the crossover, IIRC. Sulfur increases contrast and speed, gold increases speed and the combination amplify both speed and contrast. This is a general rule of thumb. Gold has a tendancy to give a soft toe while increasing speed. The combination is often foggier than just sulfur alone.

Selenium and Tellurium have also been used, but are so toxic that Kodak has abandoned their use. Fuji uses Tellurium for super sensitization of emulsions.

PE

JOSarff
08-14-2008, 07:44 PM
Kirk:

First, congratultions to you and Denise on the great workshop last weekend. I was sorry to miss it.

If you run across those graphs I would love a copy.

Joe

wildbillbugman
08-15-2008, 01:58 AM
Kirk:

First, congratultions to you and Denise on the great workshop last weekend. I was sorry to miss it.

If you run across those graphs I would love a copy.

Joe

Hey Joe,
How do you know that the Workshop was "great" as you weren't there?
(:D:DIt was great. A lucky guess on your part?)
Bill

Kirk Keyes
08-15-2008, 02:23 AM
Joe,

I just looked and it's Neblette's Eight Ed. "Imaging Processes and Meterials" from 1989. Nice 3-D graphs showing the relationship between gold and sulfur, both for cubic and octahedral crystal habits.

It also has a really nice discussion on t-grains and pAg as well.

Photo Engineer
08-15-2008, 08:36 PM
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

JOSarff
08-16-2008, 02:14 PM
Bill:

Good hearing from you. There was a rather large post in the workshop section by Don12x20 praising both Denise and Kirk for the workshop and information, and your presentation also. Melody also mentioned it when I was over at B&S to pick up a cup of KI.

Joe

Kirk Keyes
08-20-2008, 02:25 AM
Finally some time to get back to this...

PE makes a good point about the amount of gold or silver being based on the average diameter of the halide crystal.

The Neblette's book I referenced above discusses how the amount of Au and S are related to the crystal habit as well. It says that for AgBr crystals, cubic crystals are more sensitive to the amount of gold, while the octahedral crystals are more sensitive to sulfur concentration.

It also says that octahedral emulsions gain about 0.7 log E in speed for sulfur-only but only about 0.4 log E for gold only. The reverse was true for cubes - they gain about 0.9 log E in speed for gold-only and about 0.4 log E for sulfur only.

The graphs they reproduce also show this effect - for the AgBr octahedral, the optimum Au/S amount was about 1.6 mg/mole Ag sulfur and the speed kept increasing as the concentration of gold was increased. The graph shows an optimum ratio at about 2.0 mg gold/mole Ag and 1.6 mg sulfur/mole Ag. However, as was just mentioned, the speed does keep increasing as the gold concentration increases as it goes off the graph at 2.25 mg Au/mole Ag.

For AgBr cubes, there is a maximum speed gain for the ration of gold concentrations from 1.0 to 2.0 mg Au/mole Ag and 1.4 to 3.0 mg sulfur/mole Ag.

So I guess you could use the chart PE shows to figure out which crystal habit you are making to determine what ratio of Au and S to use.

Kirk

Also, PE - with all your talk of pAg lately, perhaps you should write your handle as "pE"...

Photo Engineer
08-20-2008, 09:56 AM
Kirk;

I say PU to pE. :D

As to the speed increases noted by Neblette, I think that he is rather conservative in his figures. Also, he has not included the very great gain in contrast afforded by sulfur. Sulfur alone can change an emulsion from a grade zero contact paper to a grade 2 enlarging paper with several stops in speed.

Finish formulas (sulfur + gold) are often as complex or more so than emulsion making formulas. I give "dump and stir" emulsion formulas and "dump, stir and heat" finish formulas, but the real world goes far beyond that!

PE

dwross
08-20-2008, 11:07 AM
Oh, I don't know, Ron. I think Kirk has a real flare for the pun. Have you heard his one about dry plates in Oregon? 'Our weather may be wet, but our plates are dry!" Yuh gotta love it.

re sulfur: If the conversation has moved from film emulsions to paper, 'speed' has an important related issue. My favorite handmade paper is at least as fast as Forte Polywarmtone when I enlarge a 120 negative, sandwiched with an (old fashioned) unsharp mask, to 11"x14". Minutes! Of all the things that are relative in photography, speed is at the top of my list.

The rub with enlarging onto handmade paper (in my experience) is that the paper doesn't dry flat after it has been coated with emulsion. It takes a contact printing frame to make even contact across the whole of a negative. I don't like really thick, cold press, heavily-sized papers, so I don't know if they dry flatter, and I don't have a vacuum printing frame. I would really love if someone(s) would try out one or both options for enlarging and let us know how it worked out.

Denise

Kirk Keyes
08-20-2008, 11:40 AM
Denise, speaking of Oregon weather - is it raining as much in Newport as it is in Portland? (I.e. a lot!)

dwross
08-20-2008, 12:04 PM
Yes, drat! And I've got a lightsafe of dry plates begging to be set free. The garden is happy and the fire danger has dropped to zip, so I guess there's a silver lining. But I prefer my silver linings to be emulsion. Ouch! Nope, my punning ability is no match for yours.

d

Photo Engineer
08-20-2008, 12:18 PM
Well, we had about 7" of rain in 1 month here and 3 - 5" of it fell in 72 hours. Basements flooded and pools overflowed.

As for the speed issue, I can expose at the same speed as Ilford MGIV paper, so that is not an issue with me. I use papers with high weight for enlargements, and you have seen at least one of these in the class on baryta and one on Strathmore. Mine dry kinda flat, but then maybe adding a humectant like sorbitol might help you.

You could try a 300# paper. It makes gorgeous prints and lies flat. You can make very nice postcards with it.

PE

dwross
08-20-2008, 12:45 PM
Seven inches in a whole month! I didn't realize that Rochester was in a desert. An humectant is the last thing I need :(.

Thanks for the tip about little prints. If one were determined to enlarge, I think you could find 3 x 5 inches of flat paper on about any brand of good, mid-weight watercolor paper (except maybe commercial baryta - I'll check that out next time I coat it.) Fabriano Artistico HP would certainly work.

At this point, it's only fair to admit my bias toward contact printing. Nothing (to my eye) compares.
d

Photo Engineer
08-20-2008, 01:00 PM
Denise;

I agree that contact printing has much merit. I just want to point out that the problems for making enlarging paper are minor and can be ironed out (punny?).

PE

JOSarff
08-20-2008, 02:20 PM
[
Well, we had about 7" of rain in 1 month here and 3 - 5" of it fell in 72 hours. Basements flooded and pools overflowed.

Denise, Ron & Kirk:

This has been some great information. Since I live in Santa Fe (typical humidity <10%) feel free to visit.
To the pun issue, could Kirk unlock the secrets?

Joe

Kirk Keyes
08-20-2008, 03:45 PM
Joe - I can't claim to hold the secrets to a good pun, but I did study under one of the best, and my observation of his skills was that you just have to take every opportunity, especially if it is a real groaner. There's no holding back a pun... And sometimes the best pun is the worst pun.

Next time I'm in Santa Fe, I'll swing by. It could be a few years though...

OK - now let's not turn this thread in a real pun one...

totalamateur
01-21-2009, 12:04 PM
So to calculate pAg, it's the negative log of the molar concentration of silver. In the SRAD formula posted, it's 130 g Ag to 500 ml water. That's .769 Mol Ag, and 27.7 Mol water, or a concentration of .027, for a pAg of 1.557?

if We dump that into a liter of water, with other items, and that gives us .769 mol Ag in 83.1 Mol water, or a concentration of .00923, pAg of 2.03.

Now does this change as the items react? ( I guess it would since the Agbr is insoluble)

If so, can we calculate how fast?