Measuring vAg - preliminary results!

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by Photo Engineer, Oct 8, 2009.

  1. Photo Engineer

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    One of the unstated goals of the book has been to supply the reader with a simple and inexpensive method to measure vAg. This is critical in double run emulsions, in order to know where you are in the grand scheme of things making a particular crystal.

    I have been working on this for nearly a year now, and have been able to make my first measurement of vAg today. If things work out, then I have made a major step forward for the craft of emulsion making, and I can reduce it to about 3 simple parts for the experimenter.

    Right now, I have a breadboard with pieces all over the benchtop, and the readings are erratic, but the general error with 1 M NaBr is on the order of 6 millivolts which is not bad for the first "real" setup. The error becomes larger with greater dilution. That is what I face right now.

    I would like to thank Kirk Keyes, Jim Browning and Bud Wilson for help and support in this. Without their expert opinions and help, this preliminary result would not have been possible.

    Give me some time to think on the problems and get feedback and I'll try to get better results.

    PE
     
  2. hrst

    hrst Member

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    Cool!! Keep going! I'm definitely interested in double runs and will purchase your book&DVD once it's available. I understand that while you can make the emulsion a little more monodisperse by dumping all the silver nitrate as quick as possible, still you can't control the shape of the crystal without measuring vAg and running silver and salt simultaneously at correct rate, and, the most difficult point here is the electrode and meter design.

    We are going to make our second SRAD emulsion soon, now with erythrosine and decent sulfur sensitization as well as proper subbing of acetate. I've been spending my days during past weeks reading this forum. There's so much information hidden here. Thank you to everyone who has been contributing here. This is so interesting...
     
  3. Photo Engineer

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    I am now at the stage where I get +/- about 3 mv of the calculated value with a lot of noise due to the low signal (mv range). Sometimes, due to small amounts of contamination or the phase of the moon, I get a constant offset of up to about -30 mv in my measurements. Use of a potentiometer and a bias voltage steadies the signal and I can eliminate the constant bias. So, I am making progress.

    I have built a KNO3 bridge that works and is stable. I hope to publish a complete set of instructions.

    PE
     
    Last edited by a moderator: Nov 22, 2009
  4. Photo Engineer

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    On a separate note..... Why am I doing this?

    To answer my own question, I am trying to get to the point where I can make a graded Iodide core/shell emulsion. To do this, I need to hold the vAg constant while reducing Iodide from 100% to 0% leaving an emulsion that is 100% at the core and 0% at the surface (for all practical purposes) and which is about 10% overall Iodide.

    To do this, I need to maintain a constant vAg or a known vAg for most of the make.

    I also need to use up to 4 input jets with 3 of them salt.

    This is going to be fun. :sad:

    PE
     
  5. Photo Engineer

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    But, why do this?

    The graded core shell may be able to achieve an ISO speed of 400 with Sulfur + Gold sensitization.

    :D

    PE
     
  6. hrst

    hrst Member

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    COOOOL! :D.

    Keep experimenting! Your results will be greatly valued. I'm seriously interested in making more complex emulsions one day in the future, and I'm sure I'm not the only one.

    Let's preserve this important art of creating photographic materials for practical use!
     
  7. Photo Engineer

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    I'm rehearsing in the light with 2 pumps (3 delivery systems) and a syringe, as the actual make will be too expensive to blow what with the cost of Silver Nitrate.

    PE
     
  8. hrst

    hrst Member

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    What I mean by "creating photographic materials for practical use"

    I understand well that there are many "alternative processes" that are easy and affordable ---, but they don't give enough speed or sensitivity to be of a practical use.

    On the other hand, there are many very practical (for end user) "processes" like CCD chips, but they are impossible to create at home :wink:.

    But, this silver-based emulsion making has proven it's practicalness by being in daily use even today by millions of enthusiasts and even complete laymen, and still, it is somehow possible enough for one to do at home if given enough interest and time to learn the process.

    Fictional situation: in 2030, there are less and less films to choose from, and people are uncertain how long they will be available.... If I could say: here I have a home-made 400-speed BW film with nice tone rendition and manageable grain and sharpness, and paper to print it to with nice results, I'm sure there would be many who would like to try it out - and learn the process how to do it!
     
  9. Photo Engineer

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    I believe that the home made film/paper field lies in the range of 4x5 or larger plates and in contact or slow enlarging papers. This is achievable in the home. The 35mm and graded papers will be near impossible to make at home, due to the requirements of cleanliness (dust free for 35mm) and multilayers (for VC papers).

    PE
     
  10. Anon Ymous

    Anon Ymous Member

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    Hello PE...

    Do you really need to have multiple layers in order to make a VC paper? IIRC, there are available ready made VC emulsions that can be hand coated. Or is it needed only for the full range of contrast grades?
     
  11. wildbillbugman

    wildbillbugman Member

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    "Fictional situation: in 2030, there are less and less films to choose from, and people are uncertain how long they will be available.... "

    2030 ?! I never thought of you as a "diehard optimist".
    More like 2010 !!!
    I know that I have never said this to you befor,PE, but Thank You! for the effort you are going through for everyone's sake. Reading this thread for the first time today, I am actualy getting a little "choked up". O r maybe its just the concentrar
    ted ammonia fumes.:mad:
    Bill
     
  12. Photo Engineer

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    Ok, single layer VC emulsions....

    These are specially engineered to prevent "crosstalk" between the emulsions if coated as one layer. This is presently beyond my capabilities. In fact, when I suggested a VC Azo type paper, it was roundly rejected here on APUG and so due to the difficulties, I went ahead with a graded Azo type paper.

    It is possible, but very difficult! I'll let you do it. :D

    PE
     
  13. Photo Engineer

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    Bill;

    I am happy to do this. It is a fun effort and keeps me out of trouble.

    PE
     
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  15. Anon Ymous

    Anon Ymous Member

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    Oh, got it... :D
     
  16. Photo Engineer

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    BTW, single layer color materials are possible as well. They are called "mixed packet materials". They are also very difficult to do. I'll leave them and most all color to you.

    :D

    PE
     
  17. Anon Ymous

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    :surprised: Really? So, tell me if I got it right..

    Since you don't have filters between the layers to block specific wavelengths, you need to make a mixture of emulsions, each of which is sensitive to specific bands. And the spectral sensitivity chart of each of these emulsions wouldn't be "bell-like", as it is with today's color films, but rather steep and flat. Did I get it right?

    TIA
     
  18. Photo Engineer

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    No, the spectral sensitivites of a negative-positive color paper would be exactly the same as they are today. Endura's sensitivity curves can be seen on the Kodak web site. The speed ratios would also be the same with a fast blue, medium green and slow red. (about ISO 100, 50 and 25 respectively)

    PE
     
  19. hrst

    hrst Member

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    I'm still believing in 35mm! :smile:

    After all, we have been able to make currently still just one quite decent picture on an own emulsion (this one: http://www.students.tut.fi/~alhonena/OMAFILMI.jpg ) and it happens to be a 35mm frame - or at least was before processing :D! But it wasn't ISO400 but rather ISO5 to ISO10 so there's still a long way......... Of course, dust and coating defects are a bigger problem in 35mm, but on the other hand, at least I believe, the chances that the whole frame has more uniform coating goes up, especially if you do small coatings... But I will keep my belief and try my best after learning more -- be it LF, MF, 35mm or even 16mm MP film.!


    And Bill, many people predict every year that film dies or almost dies "in few years". Nothing like that has happened so far, and new products like the new TMAX films are released even in 2008. I think it's just realism to believe that nothing will change much in 2010, or 2011, or 2012, or...... That's why I picked a date so far in the future, that no-one of us can see what it will be like --- there might be a real renaissance for film photography, or it may die almost completely! But one thing is sure; I'm going to do what I want to do, even if it was to reinvent the wheel :tongue:.

    Best luck to everyone! Keep your inner emulsions boiling!
     
  20. Photo Engineer

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    Boiled emulsions, wow, that is an old method abandoned just about 100 years ago.

    Actually, 35 mm is possible, but slitting, chopping and perfing will be complex operations as will the prevention of dust during the coating, drying and finishing process. Equipment will have to be made to help with the finishing. And, it probably will need some sort of machine to coat the lengths needed for 35mm. The thinner support is also a problem. You see, getting good subbed estar or acetate is rather difficult but glass is with us forever (or at least a long time).

    MF film is made difficult by the need for thin support as well. The paper backing will be difficult to devise and this is why I have a 120 coater. I am also saving my 120 paper backing. I have a drawer full of them.

    PE
     
  21. hrst

    hrst Member

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    My last post seems to be a bit foggy, I had too high temperature due to swine flu :D. You were right that it's quite unpredictable with these pig-related things instead of cows.... But now I'm eating these to get proper Dmax: http://www.vitabalans.fi/en2.php?k=4165

    I believe that PET will be with us for a long time now on as a rollware for many, many purposes... I've two rolls of thin 40x30 cm sheets. I'll try the corona discharge subbing as soon as possible and will report the results.

    And, 135 films with 12 or even 16 exposures could be hand-coated. They are still quite practical...

    And I have been thinking..... There's cotton and acetic acid available in grocery stores.... Hmmmmm!
     
  22. Kirk Keyes

    Kirk Keyes Member

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    Thanks for the mention above. I've made a silver ion electrode, which used in conjunction with a commercially available reference electrode, is giving me numbers that are off quite a bit from the calculated values. Well, it's just a first trial, and I expect that things will get better with some more experimentation.

    But it looks like there will be a working solution for those that are interested in pursuing it.
     
  23. Photo Engineer

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    Ok, here is a summary of several months work and a list of equipment needed.

    First, you need a high impedence VOM such as the Radio Shack 22-812, which reads in the MV range or +/- 1V on the total scale and which can reverse polarity automatically or via a switch so that you can span the range from -300 to +300 mv. as quickly as possible.

    Second, you need a silver electrode of about 20 grams weight and quite thick (about $15 - 20 depending on the spot price of silver). This would be good, heavy quality silver wire or rod of 99.99 fine. Yes, that is 99.99 fine. Anything less will cause problems at some time or another.

    Third, you need a double junction Silver, Silver Chloride, KCl electrode such as the HI5132 or HI73127. You will need filling solution for the former, and storing solution for both.

    That should allow you to set up your experiments quite nicely. It will not help you make emulsions unless you build a bridge and I am working on that right now.

    Now, with average cleanliness, I get results as follows:

    With 0.1 M NaBr I have a range of -36 mv to -70 mv with lots of noise. With scrupulous cleanliness and fresh electrodes, conditioned and cleaned with my best effort, I get -65 to -69 mv, with the calculated value of -62.6 mv.

    With 0.1 M NaCl I have a range of +22 mv to +50 mv with lots of noise. Cleaning the equiment brings my range down to 33 mv to 36 mv, with the calculated value of 36.5 mv.

    The moral of this is that cleanliness is essential. The Silver electrode corrodes and the reference electrode does not like distilled water very much and must be kept conditioned. The type of reference electrode is not important, nor is the bridge (at this time - still working on the bridge though - more later).

    Since the reference electrode leaks saturated KCl, this is not a suitable method for making an emulsion. The bridge is critical for best results.

    I hope to summarize the 1 M salt results and the KI results in the near future for you.

    At the present time, it seems that you will need 3 Silver electrodes, one each for the 3 major salts. Also, you will need 3 bridges for the same 3 major salts. And, this will not work very well in the presence of any silver halide solvents such as Ammonium Ion or the like. This is more due to the uncertainty of calculation of a correct value than anything else.

    BTW, I have verified these results with 4 VOMs, with and without stirring, but all at 20 deg C. And, in the final circuit, to stabilze the system, I may have a battery and potentiometer to allow for zeroing the system with a standard salt along with a slope control for changing salt concentrations from high to low. At the present time, if I zero the system on a standard salt, I often see a 20 mv offset (slope) as the salt becomes more and more dilute. I am working to figure out if this is a slope problem or a contamination problem or both.

    PS, the above, when detailed, has added about 6 pages to the book. You see? I have not forgotten it either.

    PE
     
  24. J. Miller Adam

    J. Miller Adam Member

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    Que es VOM?

    Also, when you say a bridge, is this a chemical or an electronic function?

    Have you ever looked into the Vernier brand of measurement probes? They are designed for classroom use, and carry a "don't use these for real science" warning, but they are very easy to use, work with a lot of different platforms (win/mac, TI calculators, some old Palms), and have several components for adapting any BNC-type commercial probe. They are very "plug&play" and would be a logical choice for the home user, IF they are accurate enough for your purposes. They also have a very large installed base, lots of High School science teacher fans, and the company does a lot of work creating supporting curriculum, projects, activities and training seminars. You can also hook them up to Lego Mindstorms robot kits :cool:! There are also software & hardware development kits. They are also reasonably priced. Jolly good fun.
    http://www.vernier.com/

    One of the folks who advertises of APUG who sells a compensating developing timer (I think) uses the Vernier usb-enabled temperature probe in his design.

    Miller
     
  25. Photo Engineer

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    VOM = Volt-Ohm Meter, a term to describe these meters.

    The equipment I am using is known to work with the measurement I am trying to take. Just any old probe will not do. Sorry.

    A bridge is a salt or wire connection between two solutions, each of which contain a solution to be measured. A post was made here earlier describing the entire procedure. Each end of the bridge is called a junction.

    PE
     
  26. Photo Engineer

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    Here is a summary of the KI tests.

    By inserting the electrodes and going ahead with the measurement, my range is about -222 to -313 mv for a 0.06 M solution. The calculated value is -276.5 mv

    My range with super clean, scrubbed and conditioned electrodes is -265 to -282 mv. These are all at -20 deg C. I can do better! I am working on an easy method of cleaning and conditioning the electrodes.

    Now back to the NaBr tests....

    My results over 2 days for 0.1 M NaBr now ranges from -62 to -63.2 mv, calc -62.6. This is pretty good right now. The 1.0 M NaBr results over 2 days is -116.2 to -120, calc -116.9. So, I am pretty close to where I want to be in measurement methods and lab technique (work flow).

    The bridges are made and working, I have worked out a gel and salt solution, I have worked out a method of filling them, and a method of storing them. There is still a lot to do.

    PE