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  1. #1
    Photo Engineer's Avatar
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    Measuring vAg - preliminary results!

    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. #2
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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. #3
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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 Photo Engineer; 11-22-2009 at 02:28 PM. Click to view previous post history. Reason: slight change in syntax

  4. #4
    Photo Engineer's Avatar
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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.

    PE

  5. #5
    Photo Engineer's Avatar
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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.



    PE

  6. #6
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    COOOOL! .

    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. #7
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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. #8
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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 .

    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. #9
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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

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    Quote Originally Posted by Photo Engineer View Post
    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
    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?

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