Any Hard Data On Silver Quantity?

I'm about to experiment further with film, paper, and fixer.
Is there any solid information, whatever the source, on the
quantity of silver in the gelatins of film and paper? Dan

This question has come up many times before but no one seems to know and none of the companies are telling any secrets. I suspect very little anymore.

There's a book from the late 80s called "Controls in Black & White Photography" by Dr. Richard Henry. He has a graph of silver concentration vs maximum density in paper.

There is not directly proportional conncetion between the two, i.e. it is not as simple as how much silver there is in a material as to how it behaves. You should look up this book before you get into some possible expensive testing.

Kirk - www.keyesphoto.com

The relationship between optical transmission density and silver was studied years ago by Hurter & Driffield who found that a unit density contained about 12 milligrams of silver per 100 square centimeters. This is after development and fixation, of course. The silver content of an emulsion capable of a maximum density of 3 will be at least 3 times that value. It is a linear relationship. That is, the amount of silver in a uniform density of 2 was about 24 mg per 100 sq. cm. The amount of silver in printing paper is about half that because the light by which it is viewed passes through the silver layer twice.

There doesn't seem to me to be much reason to expect a vastly different value for modern emulsions, except that tabular grained films may be more efficient by virtue of the orientation of the crystals.

gainer said:

There doesn't seem to me to be much reason to expect a vastly different value for modern emulsions, except that tabular grained films may be more efficient by virtue of the orientation of the crystals.

Click to expand...

Patrick - my understanding from discussions with Ron on photo.net is that these values can vary by quite a bit. The size and shape of the developed silver has a big effect on the optical density. My understanding it that silver is can be colored and that no density vs. mass relationship exists except with the same film / developer combination is repeated.

Kirk - www.keyesphoto.com

Kirk Keyes said:

Patrick - my understanding from discussions with Ron on photo.net is that these values can vary by quite a bit. The size and shape of the developed silver has a big effect on the optical density. My understanding it that silver is colored and no density vs. mass relationship exists except with the same film / developer combination is repeated.

Kirk - www.keyesphoto.com

Click to expand...

This whole silver content thing is ass-backwards. The goal, as I understand it, is to get the deepest blacks in your prints. So, if that is your objective, it is a quantity that can be measured quite easily with a reflection densitometer. Worrying about silver content presumes that you know that higher silver content definitely correlates with deeper blacks, and from what I have read, this is far from certain. Why not measure just what want in the first place and test a few papers and see for yourself? The silver content in and of itself is a side issue. To me this is sort of like the assumption that higher SEC-reported earnings means higher economic performance of a company. Maybe, maybe not. Why use a proxy when you can measure the real thing?

gainer said:

The relationship between optical transmission density and silver was studied years ago by Hurter & Driffield...

Click to expand...

This is something that has been of interest to me for some time, wondering about the effect that developing has on the environment. We hear that it is *bad* to dump fixer into the municipal water waste system because we will be "polluting the system with silver" - and I'm wondering just how much silver is flushed away in developing one roll of film or one print... and the toxicity of those silver compounds. Silver - as far as I know (which is not much) is not high on the list of toxic metals.

There is not a great deal of information here - and the data used by Hurter and Driffield has GOT to be a little "old" by now, and how closely it represents modern films and papers is somewhat suspect.

I do know of one "small lab" operator who installed an expen$ive silver recovery system - following the hype that, "You can recover ALL kinds of silver - and sell it to chemical companies for *big* money". After something like five years of "recovering" he said he did not have enough silver to equal the cost of postage to the recycling buyers.

I'm guessing that we would have to be *very* busy to produce the amount of silver contained in one Sterling Silver spoon.

Kirk Keyes said:

Patrick - my understanding from discussions with Ron on photo.net is that these values can vary by quite a bit. The size and shape of the developed silver has a big effect on the optical density. My understanding it that silver is colored and no density vs. mass relationship exists except with the same film / developer combination is repeated.

Kirk - www.keyesphoto.com

Click to expand...

I presume we are not discussing X-ray film or other special films. In what way has the dispersion of silver particles changed since the days of H&D? Their research was not restricted to one emulsion or developer. They used both organic (pyro soda, pyro ammonia) and inorganic (ferrous sulfate) developers. Later, in the 1930's, a very similar figure was quoted in "Principles of Optics" by Hardy and Perrin. The tabular grains have always been with us. You can see them in the illustrating photomicrographs in Hardy and Perrin. The modern T-grain films have a higher percentage of them and thin emulsions that tend to orient them in a more efficient way, so we might have a smaller number. My statements are quoted facts based on experimental research and I admitted that they may not apply to current films, but it is difficult to see how they could be very far off.

If you have nothing but that theory to go on, and if it is important enough to argue about, then it is time that you did some experimental research. Expose a sheet of film uniformly, develop it and measure its optical density. Recover the silver and weigh it. Divide the weight by the density and that result by the area of the film. You can do the same with slow and fast traditional films and slow and fast T-grain films. It might be a lifetime project, but at least you could state facts.

This is an aside to the silver content question asked by Dan.
Extract from The Theory of the Photographic Process; Chapter 20: Quantitative Evaluation of the Developed Image:

"Eggert and Küster measured the relation between the diameter of the grains and the photometric equivalent of various emulsions under a variety of development conditions and found that the equation
P = 1.53 x d x roh
(my note: where P is the photometric equivalent, or ratio of silver content to density; d is the diameter of the silver grains and roh is the 'effective specific gravity' of the grains - this is nowhere near the mass density of solid silver because of the structure of the grain)
derived by Nutting holds accurately. The direct dependence of P upon grain diameter makes possible the expression of the photometric equivalent in terms of the Callier quotient Q. ... P = 10.4 x roh x log Q"

Both roh and d vary significantly in pictorial films. Eggert and Küster found P to vary between 0.01 and 0.03. (Note: Patrick quoted the H&D value above, which would translate to 0.012) Experiments by Sheppard and Ballard found that a particular film, when all silver was fully developed, could have an optical density of between 1.34 and 6.00. Same silver g/cm², widely different optical densities.

Best,
Helen

Dan,

Here, to give an idea what is involved, is a summary of the relevant parts of ANSI/PIMA IT4.42-1998, the ANSI standard for determining silver content. Obviously if anyone wanted to do this they would need more details from another source and/or the full standard – I have a ‘single user license’ copy, but don’t wish to infringe copyright. All I’m doing here is providing a teaser for the exciting full-length thriller...

Two methods are acceptable: atomic absorbtion spectroscopy (AAS) and potentiometric titration (PT).

A sample of film is cut up and boiled in conc. sulphuric acid, conc. nitric acid and hydrogen peroxide. I told you it was a thriller. After cooling the solution is diluted with water and the pH is adjusted with ammonium hydroxide and glacial acetic acid.

For the PT method, the sample is titrated with potassium iodide to remove the silver ions from solution. The presence of silver ions is detected by measuring the potential between a silver electrode and a reference electrode.

Table 4 gives the expected range of silver content. Here are some extracts from the table for unprocessed pictorial film, in g/m²:
Color negative: 2.5 to 11.0
Color reversal: 3.0 to 5.5
Color positive: 1.5 to 2.5
B&W film: 2.5 to 8.5
B&W paper: 0.8 to 1.5
Color paper: 0.5 to 2.0


More later as time allows... I happened to have this text 'ready to go' for another reason, and so posted it, though I realise that it isn't 100% relevant.

Kodak quote their colour neg film as having between 5.3 (100 speed) and 8 g/m² (400 speed) silver.

Best,
Helen

Hi Ed

regarding the value of a silver recovery unit, In one 6 month period I captured $1500.00 in silver apparently 99%pure.
When this unit started to go I looked to environmental recovery systems to replace. The company I used would either sell the unit to me for $4500.00 or put it in for free and maintain the unit. They drop by 4 times a year for maintenance and every 600hrs of operation they replace the cartriges with new.
I think that no one in their right mind would go to this effort unless it was financially rewarding.
I urge all APUGers to consider this and take your fix to a local lab for proper silver recovery.
You can ask for the paperwork on the machine they use to prove that it does work to exacting standards.. we were checked this summer and passed the testing proceedure.
Any one in the GTA of Toronto can bring their used fix and used ra4bleach fix to us and we will put it in our recovery unit.

gainer said:

It might be a lifetime project, but at least you could state facts.

Click to expand...

Well, sure, Patrick - I'm all for facts. But then you need to get things right as well...

I would like to thank Helen for doing all the research that it would take to reply to your mistaken claim that silver concentration is directly proportional to optical density. Thank you, Helen.

Quoting Helen: "P = 1.53 x d x roh

"Both roh and d vary significantly in pictorial films. Eggert and Küster found P to vary between 0.01 and 0.03. (Note: Patrick quoted the H&D value above, which would translate to 0.012) Experiments by Sheppard and Ballard found that a particular film, when all silver was fully developed, could have an optical density of between 1.34 and 6.00. Same silver g/cm², widely different optical densities."

OK - so I hope we can agree that it's not directly proportional.

Here's a way to think about it - The more finely divided the silver is, the higher the optical density is for a given mass - i.e. the covering power increases.

Here's an analogy that Ron related to me:
Take 1 cubic yard of sand and spread it over 10 square yard of space and then take one boulder (made of the same material as the sand) that has the same mass as the 1 square yard of sand and place the boulder (intact) in a 10 square yard space. The boulder may have a smaller volume than the sand, but it has the same mass. Measure the transmitted density of this 10 square yard with each covering material (ie - the thinly divided sand or 1 single solid boulder). Which material would have the higher optical density? I hope you find the answer is as intuitive, logical, and also scientifically correct as I do.

Here's an example that Ron had sent me:

"Anyhow, I can give this example. The finely divided yellow silver filter layer in films that is used to filter out all blue light in color films, is used directly under the yellow (top) layer in ALL color films. It has a density of nearly 3.0 but in silver weight is about 100 mg/sq m. This would require 10 - 30x more silver to achieve from normal silver development in a film depending on the form. The yellow colloidal silver is called Carey Lea Silver after the inventor.

"This same is true for the gray silver used as an antihalation / antistatic layer on the back of some films. It has a density of nearly 3.0 as well for the same quantity of colloid.

"The finer divided the silver is, the higher density for a given mass - the covering power increases.

"Tabular or lump silver has the lowest density."

I hope you'll remember this Patrick as I've seen you make this claim in other threads before.

Kirk

Helen B said:

Two methods are acceptable: atomic absorbtion spectroscopy (AAS) and potentiometric titration (PT).

Click to expand...

Dan - I have experiance with both of these analytical techniques - if you have any questions feel free to ask.

Also, would you be willing to discuss what your avenue of research is here?

Kirk

Kirk mentioned Dr Henry’s tests on B&W papers. Here is some info from the 1988 second edition of his lively book. I’ve converted his mg/in² to g/m². The first number is silver in g/m² determined by Dr Henry. The second number is density calculated as max black minus max white. The third is silver content divided by density.

Ag D P
Ilfobrom Grade2: 1.41 2.22 0.64
Galerie Grade2: 1.57 2.3 0.68
Kodabromide F Grade 1: 1.36 1.8 0.76
Kodabromide F Grade 5: 2.60 1.85 1.41
Brovira III Grade 2: 1.40 2.26 0.62
Portriga Rapid III Grade 3: 1.43 2.45 0.58
Seagull Bromide Grade 2: 1.95 2.13 0.92
Brilliant Grade 2: 1.36 2.11 0.65
Kodak Polyfibre F: 1.80 2.21 0.81
Kodak Elite S2P: 1.60 2.12 0.75

Best,
Helen

Now this is my field as I work in precious metal recovery, the 10 yrs previous were as a Photo-chemist/ Emulsion manufacurere & Photographer.

No there's almost no silver at all used in films now or paper, but we'll stick a unit in to make sure your fix & dev can go to drain compliant.

Am in cynical mode, but thats how people are treated by most companies.

The answer is yes the silvers there make sure your in control

Ian,
Can you post some emulsion formulas so if the film manufacturers go under, we can make our own film? I'd love to try my hand at emulsions.

So what you are telling me is that if I superpose two Wratten gelatin filters each of density 1.0, I will not have the equivalent of a Wratten filter of density 2.0. Sorry, I don't believe you. If the two are in contact so that there is no question of loss due to reflection between them, you will measure the density as 2.0. Three of them will get you 3.0. You know that as well as I. You can do the same with two pieces of film. The density of the sum will be the sum of the densities.

That statement did not originate with me. It was made and proved by Hurter and
Driffield.

"Experiments by Sheppard and Ballard found that a particular film, when all silver was fully developed, could have an optical density of between 1.34 and 6.00. Same silver g/cm², widely different optical densities."

Different developers as well, I bet. Such a statement does not bode well for tables of development time and temperature, does it?

The examples you quote from Ron are rather far fetched analogies of the films we use.

If you want to estimate how much silver you can recover from undeveloped film or from the blix of color film, you need to know the silver content of that type of emulsion, which as you have shown has a wide variation with film and type of film.

If you want to estimate how much is left in developed film, you need to know the average density and the photometric equivalent.

For the purpose of silver recovery, it would not be efficient to develop unused black and white film before recovery because many, if not most developers will dissolve some part of the silver and carry it away even before it gets to the fixer.

Hardy and Perrin, in the 1932 edition of "Principles of Optics" said that the photometric equivalent is about 0.00010 grams per square centimeter per unit density, with some variation with type of medium. Helen quoted a range of 1 to 3 times that value among pictorial films. That is well within what engineers call "an order of magnitude". The variation from batch to batch of the same type of emulsion is probably much less. I would be willing to bet the value of silver in a standard roll of film (in other words, a nickel) that the film manufacturers are striving for the lower number, even though that is not the major cost of film.

Helen B said:

Dan, Here, to give an idea what is involved ...
Two methods are acceptable: atomic absorbtion spectroscopy
(AAS) and potentiometric titration (PT).

...from the table for unprocessed pictorial film, in g/m²:
B&W film: 2.5 to 8.5
B&W paper: 0.8 to 1.5

lKodak ... colour neg ... 5.3 ISO 100 and 8 g/m² ISO 400 silver.
Best, Helen

Click to expand...

Those two ANSI methods are not suitable although I'll keep
the PT method in the back of my mind . I'd think it low
cost and easy to do.

Quite a range in silver content. Those B&W paper amounts,
above, are quite low compared with those listed with
your latter post.

My determination of a gelatin's silver content will start with
an extraction using sodium thiosulfate. Two extractions
should pull 99% plus of the silver.

Assuming the ideal, I've then a solution of complexed silver,
sodium, and some halides. I'll have to work from there for
a quantitative determination of the silver. Dan

dancqu said:

Quite a range in silver content. Those B&W paper amounts,
above, are quite low compared with those listed with
your latter post.

Click to expand...

Remember that on papers, the light travels through the silver twice, once on its way in, it then bounces of the base material, and then comes back through the silver. So you will not need as much silver in a B&W print the uses reflection as you will for a B&W negative that uses transmission.

Kirk

dancqu said:

Those two ANSI methods are not suitable although I'll keep
the PT method in the back of my mind . I'd think it low
cost and easy to do.

My determination of a gelatin's silver content will start with
an extraction using sodium thiosulfate. Two extractions
should pull 99% plus of the silver.

Assuming the ideal, I've then a solution of complexed silver,
sodium, and some halides. I'll have to work from there for
a quantitative determination of the silver. Dan

Click to expand...

Low cost and easy - that's what the potentiometric titration method is for! Much cheaper than using an AA.

OK - so you have silver in a thiosufate solution. One way, I'm not sure it will be easier, is to electroplate the silver onto a silver electrode. If you know electronics, you could do it that way. But now you need a way to measure milligram levels of wieght accurately.

And you may be able to do a potentiometric titration on the fixer solution, but I'm not sure about that. Usually, these titrations use a "silver" electrode (different than the simple sheet of silver metal I mentioned for the electroplating), here we're talking about an "ion selective electrode" and you use a titrant that will pull the silver out of solution through precipitation.

In the method Helen discussed, the sulfuric will digest the organic materials in the solution along with the help of the peroxide, and the nitric, along with the peroxide will make silver nitrate which is very soluble. At the titration step, the potassium iodide will make silver iodide, which is extremely insoluble, and it will drop out of solution. For this test, you will need a silver electrode and a pH meter that can read in millivolts.

The problem with titrating a thiosulfate solution with iodide is that the silver iodide will still be soluble in the solution. That's why they convert the silver into a nitrate in a solution that has no thiosulfate.

Patrick wrote: "So what you are telling me is that if I superpose two Wratten gelatin filters each of density 1.0, I will not have the equivalent of a Wratten filter of density 2.0. Sorry, I don't believe you."

Patrick, firstly, I beleive this thread is about "Is there any solid information, whatever the source, on the quantity of silver in the gelatins of film and paper?"

I addressed this issue by suggesting that Dan look at Henry's book, where he measured the optical density vs. concentration of silver in the material and stated that there is not a direct proportion between the two.

So now you are implying that I am claiming that optical densities are not directly additive - I am not saying that. I do agree with you that they are. I am saying that silver concentration is not directly proportional to optical density. Are the formulae and values that Helen graciously supplied not sufficient to convince you of that?

And where are you changing the silver size (but not concentration) in the example you gave above to demonstrate your point? You did not, you simply added two materials together and implied that I am incorrect in my claims.

Patrick quotes Helen, "Experiments by Sheppard and Ballard found that a particular film, when all silver was fully developed, could have an optical density of between 1.34 and 6.00. Same silver g/cm², widely different optical densities."

Patrick responds, "Different developers as well, I bet. Such a statement does not bode well for tables of development time and temperature, does it?"

??What are you talking about here?? Your statement does not have anything to with what Helen quoted above.

Patrick said, "The examples you quote from Ron are rather far fetched analogies of the films we use."

Sorry, I thought that was a pretty simple analogy that would show how two identical optical densities could be obtained using equal concentrations of materials. Granted, the analogy pushes the example to the extreme, but I found it to be very easily understandable. I figured you would be able to see how the analogy applies to actual materials - would you like me to reword it?

Patrick continues. "If you want to estimate how much is left in developed film, you need to know the average density and the photometric equivalent.

Yes, and notice you used the word estimate - I think we were discussion measuring actual quantities?

Patrick said, "Helen quoted a range of 1 to 3 times that value among pictorial films. That is well within what engineers call "an order of magnitude"."

Sure, it is within an order of magnitude, and if we were working with our sliderules on the back of a napkin while out at lunch, we should be happy with results within an order of magnitude. But it still doesn't mean that the relationship between silver concnetration and optical density are directly proportional.


Patrick said, "The variation from batch to batch of the same type of emulsion is probably much less."

It better be much less, otherwise you will have an out of control situation on your production line and produce a rather crappy product.

Kirk

It should be noted that, as Helen pointed out, in Henry's work the Dmax of the papers was measured. The reflection density of materials is limiting (because of the reflection) and it gives a bias. Henry missed that. But then Henry was testing to determine whether the urban legend that more silver in papers gives a higher Dmax so I find his work still usefull.

My understanding is that todays fine grain emulsions are on the order of 0.2 micron, but Carey Lea silver, is 0.009-.011 micron. Carey Lea Silver is the finely divided yellow silver filter layer in films that is used to filter out all blue light in color films, is used directly under the yellow (top) layer in ALL color films. It has an optical density of nearly 3.0 but in silver weight is about 100 mg/sq m. This would require 10 - 30x more silver to achieve from normal silver
development in a film depending on the form.

I beliece that high speed T-Grain emulsions have grains on the order of about 2.0 microns. So, the 0.010 vs 2.0 micron was the analogy I was trying to make by using the the sand and boulder example.

Kirk

Ron Mowrey has started a parallel discussion with responses to this thread over at--

Dead Link Removed

Kirk Keyes said:

So you will not need as much silver in a
B&W print the uses reflection as you will for a B&W negative
that uses transmission. Kirk

Click to expand...

Helen B posted in each of two posts the amounts of silver
in B&W PRINT materials. Those amounts differ by quite a bit.
She did not give a source for the amounts mentioned in
her first of the two posts. Dan

Dan wrote:
'She did not give a source for the amounts mentioned in
her first of the two posts.'

Yes I did.
Table 4 of the ANSI standard.

'Here ... is a summary of the relevant parts of ANSI/PIMA IT4.42-1998, the ANSI standard for determining silver content. ...
Table 4 gives the expected range of silver content. Here are some extracts from the table...'

Best,
Helen