How much silver is there in film?

Discussion in 'Film and Processing' started by James G. Dainis, Jul 28, 2004.

  1. James G. Dainis

    James G. Dainis Moderator

    I realize it is usually not viable for the average hobbyist to try
    to reclaim silver from exhausted fixer. But, I have always been
    curious as to how much silver is actually in film and photo paper.
    Also, how thick is the emulsion?
  2. The Bass brothers might be able to alter the price of film, but we'll never be able to change their net worth extracting the silver in it...
  3. Agfa Multicontrast Premium contains approx 1.5 grams per square meter (according to their data sheet).

    Not sure about film.

  4. Back in my days at Hollywood Cine Labs in Burbank,CA,I once asked Chuck Kemmerer,my Kodak technical service rep this very question.In an unexposed roll of B&W 35mm motion picture camera film,there is approximately 1 ounce per 1000 feet.A 1000 foot reel of 35mm B&W projection film has around a 1/2 ounce.We used to run old cartoons and scrap B&W films throught the bleach,and fix on the color processor.This would yield almost exactly, a 1/2 once per 1000'.
  5. And to answer your other question, the full gelatin coating (including subbing layers, antihalation layer, and overcoats) for most modern films runs between 1/1000 and about 3/1000 of an inch, on a base material that runs from around 2/1000 up to 8/1000 (the latter for sheet film, the thin stuff for microfilm that feels like audio tape).

    And if you think in metric (I do only when I need to), there are 25.4 millimeters in an inch.
  6. James;

    To be more specific, each imaging layer in film or paper runs from 100 to 300 microns thick and interlayers range from 10 - 50 microns. There are also overcoats and undercoats to consider. They will be in the range of 10 - 50 microns as well.

    The silver in each layer varies, but the average grain size I have seen published for film emulsion is about 1 micron. Paper emulsions are much finer grained as are print films.

    Silver laydown is covers a wide range. X-ray film has as much as 18 grams / sq M, due to being coated on both sides. B&W paper may have as low as 0.9 g / sq M. In color films and papers the grain sizes and sliver laydown in each layer is adjusted for the speed and curve shape. A good average for color paper might be about 1.5 g / sq M on the high side and 0.4 g/sq M on the low side and color film might be 3 - 5 times higher. But this varies quite considerably.

    During development, you could use an average of 50% being developed to form the image, and therefore 50% would be fixed out in B&W but all of it would (hopefully) be removed in color.

    If anyone out there finds errors in my math, it is because I never used this type of measurement when I made a coating. Other units are used, and I had to do a quick rough conversion.

    Hope this helps.

    Ron Mowrey
  7. James: According to sources I've read, not enough to worry about. Sensitizing dyes and other components are at least as important as silver. The term "silver rich" is just something we like to wax nostalgic over when we look at older photos that seem more original or interesting than our own.

    Marshall: That was the Hunt brothers who were obviously misled by the notion that hard assets such as silver, gold, diamonds, etc., are all that's required to play with the big boys. The big boys are mostly old money and have better control over the values of precious metals and gems. The nouveau riche, even Midwestern oil money riche, can get their assets kicked fooling around with old school European money. Even Bill Gates is rumored to be deferential to the less wealthy but well established old money families.

    The Bass family in the Fort Worth area is a whole 'nuther breed. Unless someone has information to the contrary I don't see that they've done anything but benefit the community with their wealth.
  8. When silver got to $50/oz, it became of critical importance to the entire photographic industry. One of the raw materials increased in price by 10x. What would you expect them to do, sit on their thumbs?

    So, the level of silver went down in some color products by means of increasing coupler reactivity, efficiency of development, and the coupler 'equivalency'. Old couplers required 4 moles of silver to produce one mole of dye, but new couplers required only 2 moles of silver to produce dye.

    This move allowed a 50% reduction in silver and it allowed the introduction of the blix.

    Ron Mowrey
  9. And I always assumed that the silver prices had something to do with introduction of the disk camera. Less silver, more plastic.
  10. Blix = combination of bleach and fixer in a single step (right?)
  11. Blix = bleach + fix. Yes.

    Also, you can only reduce silver so much and then the granularity starts to get worse. Less silver = more grain. Less sliver = less sharp as well.

    It is a fine tradeoff to balance these.

    Ron Mowrey
  12. Ron,

    You missed a bit on that one. Less silver=more sharp (less turbidity). Less silver also means greater capability for color correction/saturation. More color correction means more grain. So this is where the real balancing act starts!

    Perhaps one of the most underappreciated facts is that grain performance is not independent of other desirable features in a film.
  13. Joe;

    Thanks for the comments. My memory seems to have a glitch in it though.

    I had in mind the fact that lower silver led to less released iodide or DIR inhibitor and therefore led to less apparent sharpness due to lower edge effects. This overwhelmed the turbidity issue.

    At least I seem to remember that problem in some low silver coatings in spite of the lower turbidity. I agree that if everything else were equal, the sharpness would go up with lower silver due to lower turbidity, but in my experience (much more limited that yours) everything was not equal. We went up in silver and up in absorber dye and got better sharpness via better edge effects. Any comments?

    I agree on the granularity issue. You have explained the reasoning more clearly behind my comment. Thanks.

    Ron Mowrey
  14. I forgot to add, with lower silver, oxidized color developer diffuses further thereby causing less sharpness.

    Ron Mowrey
  15. Ron,

    We're probably into discussing secondary or tertiary effects and/or reversal/neg differences (and boring our audience to death). :) If color correction is kept constant, lower silver will generally result in higher grain and higher sharpness. (If you allow everything to simultaneously change, generalizations are impossible. As I said above, lower silver tends to increase color correction in color neg which could have the effect of increasing sharpness, not reducing it. This just gets too complex if generalizations are desired. I like the simpler idea of less turbidity leads to higher sharpness.)

    We're also quite far off the topic. For common color neg films elemental silver coverage is in the range of 2-10 grams per square meter, and emulsion thickness is about 20 microns.
  16. Joe;

    I agree that generalizations are kind of hard. I have seen variations in sharpness as you describe go either way depending on what you keep constant. Lets keep to B&W for a minute then. If you decrease silver, sharpness goes up. If you increase silver level grain goes down as you have more silver centers to produce a given density. This is the simplest case and leaves out color.

    Thanks for the correction.

    Our figures are close on the silver laydown, but I sure missed the thickness. I guess that I was off by an order of magnitude due to faulty memory. So thanks again for that.

    Ron Mowrey
  17. It may be of interest that Hurter & Driffield found that the amount of silver in a uniform density of 1 was 0.0104 g/100 square cm. This number gives an idea of how much silver could be recovered on average from exposed and deveoped film. The amount is somewhat less for tabular grained film because the orientation of the flatter grains is more efficient at producing density.
  18. In my experience, that figure can vary quite widely due to the covering power of different forms of silver.

    The silver formed by some paraphenylene diamine developers during color development has very low covering power due to the extremely fine filmaents formed. Therefore, a very low density is observed per unit of mass of silver.

    This is also true for many 'compensating' developers. The form of silver changes even in one exposure from dmin to dmax and therefore covering power in mass units is not constant.

    I have plotted this up several times for experiments that I conducted.

    Ron Mowrey
  19. H&D compared Pyro-soda and Ferrous Sulphate developers in the tests I read about, but the Pyro-soda was not of the staining type, having 50 g sulfite and 50 g soda (sodium carbonate) per liter.
  20. Patrick;

    My work was with color developers and comparing them to D19, D76, and Elon Ascorbic acid. Analyses were done by x-ray fluorescence.

    I doubt if H&D had x-ray fluorescence to work with and that their accuracy could match our present methods.

    Ron Mowrey
  21. Read the book before you judge their accuracy. Besides, no one asked for an accurate assay. The original poster wanted an estimate of how much silver could be recovered from film.

    The book is:

    "The Photographic Researches of Ferdinand Hurter & Vero C. Driffield"
    edited by W. B. ferguson, published by The Royal Photographic Society Of Great Britain.
  22. Patrick;

    Then to be more specific, I have found that by using different developers, the actual silver in mg/sq m to achieve a given density may vary by nearly an order of magnitude depending on film, halide content, and developer type.

    This is related to not only developing agent, but the iodide content in the film and adsorbed species such as sensitizing dyes which change morphology of the developed silver image and therefore density / unit mass.

    Therefore, a density of 1.0 could represent a wide percentage of actual silver metal based on silver halide coated. The percentage or mass / density value varies from Dmin to Dmax and can be seen if one measures density vs wavelength of each step in a step wedge and plots this vs a similar vacuum deposited carbon wedge. Since the carbon is uniform at all wavelengths, the difference beween the carbon wedge and the silver wedge produced by development will show the variation caused by developers and halide type.

    One developer with one film is repeatable in terms of mass / unit density or density / unit mass, but varying film and developer will not yield a really useful figure.

    I agree with the fact that most developers that yield good black images from toe to shoulder will probably yield similar or even identical results, but warm or blue images, or those generated by compensating developers will most likely not fit this 'norm'. I might add that if H&D used an orthochromatic film with K grains and relatively fine grain and low iodide content (as I'm sure they did back then) the results would be quite different from todays T-grain panchromatic highly sensitized high iodide emulsions.

    When I joined EK, one of the lessons I learned was to avoid this 'trap', when I was taught the meaning of 'silver criterion' which included the need to base development on mass, not density. Note that I said development not image. Image is based on density, not mass. That was the nature of one of my first lessons at EK.

    As a rule of thumb, I learned also that about 50% of the coated silver is developed in an average image.

    Ron Mowrey

Share This Page