Any Hard Data On Silver Quantity?

[Ian Grant]

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.

I could post a number of emulsion formulae, for films and paper, after all the pre-war Agfa formulae were published after the war, and somewere I have photocopies, plus I could tell you how to make them easily on a smale scale.

However the emulsions I made were patented and although lapsed, still commercially secret 19 years after they were last produced, and strangely the later tweaks and advances were never written down properly, just notes on the lab wall, I was manufacturing batches of emulsion twice a week and it was second nature.

As I'm in the middle of a huge clearout at home I'll come across or dig out the Agfa data and post here in the cooking section in the next few weeks.

Ian

Ian

 

[Jorge]

I could post a number of emulsion formulae, for films and paper, after all the pre-war Agfa formulae were published after the war, and somewere I have photocopies, plus I could tell you how to make them easily on a smale scale.

However the emulsions I made were patented and although lapsed, still commercially secret 19 yeras after they were last produced, and strangely the later tweaks and advances were never written down properly, just notes on the lab wall, I was manufacturing batches of emulsion twice a week and it was second nature.

As I'm in the middle of a huge clearout at home I'll come across or dig out the Agfa data and post here in the cooking section in the next few weeks.

Ian

Ian

Please post them Ian, I am very interested on this, and of course your observations will be very valuable.

 

[Bob Carnie]

Hi Ian
Were you making emulsions to coat on paper for your own personal printing, much like liquid light. I would be very interested to here your thoughts on this.

 

[Ian Grant]

Please post them Ian, I am very interested on this, and of course your observations will be very valuable.

Will post them when I can find them, I copied the original source onto film, if I can't find I do know where these negatives are.

Ian

 

[Ryuji]

That's right, many German formulae from WW2 era are published in post-war intelligence reports. However, those formulae are really obsolete. Today's photographic gelatin is very different from those days, and who knows exactly what kinds of gelatin they were using. Plus, they were using obsolete agents that people don't use any more - hydrolyzed albumen, milk, saponin, etc. Those formulae are good for historical study or something but they are of little practical value even if one wants emulsions of that time.

That said, making a very primitive emulsion isn't hard. Making ones that have enough speed, contrast and maximum density with little fog requires "strategy" and experiments. It can be done and it has been done.

(I'm posting this because I somehow found this thread through google. I'm not sure if I check this regularly...)

 

[Ryuji]

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.

The relation between optical density and amount of silver is a lot more complicated than that. It is influenced by the size and shape of silver halide particles as well as the nature of the binder. My enlarging paper emulsions are usually made to give good black at 2-3g per square meter but plate emulsion needs to be quite a bit thicker than the paper emulsion to get similar density. Practically useful Dmax is also influenced by how the emulsion is sensitized... even a simple sulfur sensitization can improve a bit on this over the primitive emulsion.

With same AgX crystals, binders that swell more tend to give higher Dmax. It's a dream of emulsion makers to have binders that swell a lot but maintain good mechanical strength. Non-gelatin polymers are often blended to balance these factors, but then adhesion to the film base is another problem.

In short, there's no simple relation between silver coating weight and Dmax.

 

[Ryuji]

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.

Since early years we have much better ways of sensitizing silver halide crystals. That is, we get more speed per grain size. THis alone already helps to save silver while maintaining comparable Dmax.

Tabular grains are seen in even primitive emulsions. But the major difference is that modern tabular grain emulsions consist almost entirely of tabular grains of very uniform aspect ratio. There are a number of manipulations that can be done to these crystals to modulate the photographic properties. Anyway, tabular grains help to save silver as well.

I also have hard evidence about at least some of these things. I've been making test emulsions for some time, and ones with big grains usually don't make good black. I generally try to make extremely fine crystals for enlarging papers and use multiple sensitization techniques to make up for the speed. This way I can get much richer blacks (and better toner responses) with less silver. YET my emulsions are still less silver-efficient than those by major manufacturers. Partly because of my limited setup and knowledge, partly because of surface treatments of paper substrate.

Anyway, I wouldn't use those old numbers for today's commercial products.

 

[Ryuji]

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

Do you happen to know if those numbers are for silver nitrate equivalent, actual silver halide or metallic silver equivalent?

 

[paul ron]

Most of those papers are out of production.

 

[Kirk Keyes]

Do you happen to know if those numbers are for silver nitrate equivalent, actual silver halide or metallic silver equivalent?

Ryuji - Dr. Henry's book states "mg Silver per square inch", so that sounds like silver metal, not halide.

Good to see you post here! Thank you.

Kirk

 

[Helen B]

Ryuji,

Welcome to APUG!

Further to Kirk's reply, here's Henry's words:
'... I analyzed 10 different papers, including 1 RC paper and several of the
papers in different grades, for silver content of the emulsion using the
volumetric, potentiometric method of Bush et al.' (Bush, Zuehlke and
Ballard, Analytical Chemistry 31: 1368, 1959).

Regards,
Helen

 

[Ryuji]

Ryuji - Dr. Henry's book states "mg Silver per square inch", so that sounds like silver metal, not halide.
Kirk

Thank you and Helen for the followup. If those numbers are indeed for metallic Ag per square meter, then my emulsions aren't worse than the average of those (a decade old) products

AGFA publishes their coating weight as well. I recall MCC and MCP had coating weight of 1.5g Ag/sq.m.

I tend to think in terms of silver nitrate equivalent. In literature, different people go by different units...

 

[removed account4]

sorry it took me so long to find the link -
while it is for commercial shooters, they will still
get mad as hell with you if are a hobbiest dumping chemicals
down the drain.

http://www.narrabay.com/permitsfees.asp

its been a few years ( i am not in providence anymore ) it isn't 10K$ a day now, it is 25K$ a day for non compliance ...

 

[Ed Sukach]

sorry it took me so long to find the link -
while it is for commercial shooters, they will still
get mad as hell with you if are a hobbiest dumping chemicals
down the drain.
http://www.narrabay.com/permitsfees.asp

Checked it out. Not a word or number for silver or silver-based compounds.

So far as I've been able to determine... and I would genuinely WELCOME any hard information to the contrary, no one cares much if less than 25 gallons (100 liters?) is discharged into the most sensitve water supply - a flowing stream or brook - as long as it is not from a "commercial" lab.

I would imagine Plutonium would be an exception to the above, but I don't think much, if ANY is being produced in other than "commercial" facilities.

 

[Photo Engineer]

Just a few quick comments here.

At Kodak, it is common to assume that 25% - 30% of the coated silver is used (developed) in an average image. Seasoning tests are run with a 30% flash level to simulate this, and it works very well with the equations developed for determining process solution consumption.

This means that about 60% - 75% of the silver is fixed out and remains behind in the fix bath.

Average B&W papers contain about 100 mg/dm sq of silver (as metal) and average B&W films containe about 200 - 500 mg /dm sq, not counting X-ray which is much higher. (over 2 mg/dm sq). These are very very rough ball park figures for all cases. The presence of 'dead grains' often accounts for a lot of undeveloped unused silver halide in a coating and it varies widely from manufacturer to manufacturer and from emulsion to emulsion.

Use of a sulfur or sulfur gold sensitizer 'activates' grains and raises contrast as noted by Ryuji. Often, after this treatment we see an increase in the maximum amount of silver developed in a given emulsion by 'activating' dead grains that would otherwise not be exposed or developed.

Exact figures for coated silver are obtained in quality control by using X-Ray fluorescence, and the amount can be determined to less than 1 mg/dm sq.

Prior to coating, the melted emulsion is also analysed to determine and insure that the correct quantity of silver is present. If it varies by a small amount, a correction factor is applied to the pumping rate of the coating machine, but if the error is too large for this type of 'on the fly' minor correction (greater than about 1% or so) then the emulsion is scrap. This tolerance is part of the formula.

There is no correlation between silver density and silver mass. Helen's information is correct. This is especially true in paper where multiple internal reflections (going back to Kirk's post) cause attenuation of the density faster than silver mass rises, and therefore there is a maximum density obtainable in paper of about 2.4. Attempts to go above this denstiy value are just wasting silver, but they do alter the upper scale curve somewhat.

The maximum density of paper is more dependant on surface characteristics (matte vs glossy for example) than on the amount of silver coated, once a certain density level is achieved. This is usually about 1.8 for matte and 2.0 for glossy with a dmax being almost always lower for matte materials than for glossy materials. Again, this is just a generalization, as it varies with type of matting material and type of gloss.

Both starch and methyl methacrylate beads have been used as matting materials, as have silicon dioxide (glass or sand) and other materials. These impact on curve and apparent dmax.

Films have no practical maxiumum desity cutoff.

Silver is never neutral in color. It has a different color based on particle size and shape, and is often brownish or blueish. That is why the best step tablets are made from cast carbon in glass. These are truly black and really expensive. They are used at Kodak for critical work in the lab for quality control, as the standard silver step tablets are not good enough.

This is probably more than anyone ever wanted to hear on this topic, but I thought I might post this as an FYI for those who did.

PE

 

[gainer]

I can't believe I was so rude.
If as we know, the amount of silver in the various modern emulsions is not accurately known, and the purpose is to make an emulsion, then we can start with the value found by H&D and see what it produces. There are so many other factors that enter into the relationship between optical and silver density that is is a wonder they found so little variation. I'm sure that they called the optical effect "density" because there was a direct relationship between the amount of silver per unit area and that effect in a given emulsion.

If the desire is to know how much silver we are throwing down the drain, lots of luck if you want any precision.

 

[Photo Engineer]

Patrick, I'm sorry but optical density and mass or "density" of a material in units of weight have little relationshiip when it comes to particulate matter such as silver in gelatin.

There is a relationship between the mass of organic dyestuffs and weight per unit area, but it is usually only linear with mass if the dyestuff is cast, not dispersed as in particles and it does not work on reflection support, only by transmission density.

This relationship is unique to each organic dyestuff and is called extinction coefficient. Some of these values range up to the hundreds of thousands of units / mole of dye.

Silver metal or indeed any colloidal metal has no such thing as an extinction coefficient and can have none as they do not transmit any light. Colloidal metals allow light to pass through interstitial gaps and while doing so the light bounces around in there with some being absorbed due to the nature of the particles, and hence the color of the colloid. The size and shape of the colloid affects the frequencies absorbed, and therefore silver colloids can be made in practically any color you wish by adjusting the size of the particles. This, of course also affects the absorbance per unit of mass.

You might think of dyes as being like the atmosphere absorbing light, while silver is a haze in the atmosphere and scatters the light changing its color by the scattering power. That is a very rough analogy.

The dyestuffs do transmit light. That is different.

Early workers in this field were incorrect to assume a linear relationship between the mass of silver and its density under all conditions. That does not obviate the work of H&D, because there is an exact relationship between each unique silver image vs log Exposure for each development condition. Therefore, the work of H&D stands, but is merely a reference for the exact test conditions applied. (developer, time, temp, emulsion and instrument for example) And, as a test condition it can be repeated with exactitude if the calibration of the test is maintained. Therefore, ISO values and contrast values can be measured and obtained around the world, but only if the standards are adhered to.

On average, I use 60% myself going down the drain (so to speak). And for paper, I assume 100 mg/dm^2 and for film I assume B&W and color to be 300 mg/dm^2 as reasonable starting approximations.

PE

 

[removed account4]

Checked it out. Not a word or number for silver or silver-based compounds.

So far as I've been able to determine... and I would genuinely WELCOME any hard information to the contrary, no one cares much if less than 25 gallons (100 liters?) is discharged into the most sensitve water supply - a flowing stream or brook - as long as it is not from a "commercial" lab.

I would imagine Plutonium would be an exception to the above, but I don't think much, if ANY is being produced in other than "commercial" facilities.

ed,

their phone number is on their website, you are welcome to give them a call and talk to them if you think i am pulling your leg. when i had a studio+lab in providence, they told me (paraphrased) "if you making money from the photographs you make, you are required to get an epa permit and a permit from us. if you dump your chemistry, we will find out and you will be fined." it had nothing to do with mini-labs or commercial labs ...

i know someone in providence who was fined a ton of money by the nbc (this was when it was 10K a day), he was pretty much forced by the commission to shut down his darkroom, and he shoots lots of digital now.

 

[Ryuji]

I don't know why Narraganset area is so strict about dumping, but I bet it is because of waste water treatment system.

In 1990s, London Dumping Convention entered into effect and photographic industry could no longer dump waste chemicals into ocean, even after removing harmful substances. Environmental concerns rapidly raised. In areas with sensitive environment, or insufficient waste water treatment facility, the regulation of dumping may be more stringent.

This is exactly the reason why companies like Konica put so much effort in minilab machines to minimize the waste chemical, because the disposal cost of the waste was raised during 1990s. These days those machines use all sorts of techniques to rejuvenate chemicals to minimize the rate of replenishment, and even so, they use dry chemicals in tablet form to throw into the tanks, to minimize fluid overflow!

Either way, I bet this problem is way beyond purely scientific exercise, and it's more of global and local politics.

 

[Ryuji]

I'm sure that they called the optical effect "density" because there was a direct relationship between the amount of silver per unit area and that effect in a given emulsion.

This is not so. Even in the same emulsion, the optical density to silver content ratio (called covering power) varies depending on development. In highlight region of many emulsions, the amount of developed silver is roughly constant although density may continue to rise. This is because of increasing covering power in the particular condition of development that occurs on heavily exposed grains but not on lightly exposed grains.

In other words, developer formulators can exploit this property and try to change the shoulder characteristics a bit. (Unfortunately, the change obtainable from modern camera negative emulsions is not as big as one could get with older negative emulsions, or even some of the modern graphic art films...)

 

[Ed Sukach]

ed,

their phone number is on their website, you are welcome to give them a call and talk to them if you think i am pulling your leg.

Oh, PLEASE!!!

I DON'T think you are "pulling my leg" or lying, or inferring anything not true. I NEVER meant anything I wrote to be interpreted as anything like that - not even remotely.

I only asked for some source of HARD information. Telephone conversations, by their very nature, are soft and nebulous, and subject to wide areas of interpretation.

Will I call some governmental agency in Rhode Island for their OPINION? - With nothing established in hard copy? I don't know - it just doesn't seem very useful for me, in Massachusetts.

 

[nworth]

I don't know why Narraganset area is so strict about dumping, but I bet it is because of waste water treatment system. Either way, I bet this problem is way beyond purely scientific exercise, and it's more of global and local politics.

I bet it is a plain political power play taking advantage of "environmental concerns of the public." It almost certainly has no rational scientific basis.

 

[Kirk Keyes]

This relationship is unique to each organic dyestuff and is called extinction coefficient. Some of these values range up to the hundreds of thousands of units / mole of dye.

Homer Simpson would remind us to check out Beer's Law...