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  1. #21
    Photo Engineer's Avatar
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    On plates or on paper?

    Use 10% chrome alum and use about 2 ml on plates and 5 ml on paper. But then we don't know which emulsion and what the gelatin content is. That is important!!! My assumption is 5 - 10% gelatin. And processing at 68 F (20C). And using no Dektol or stop bath. These are all critical concerns. Or can be.

    PE

  2. #22

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    Quote Originally Posted by Photo Engineer View Post
    On plates or on paper?

    Use 10% chrome alum and use about 2 ml on plates and 5 ml on paper. But then we don't know which emulsion and what the gelatin content is. That is important!!! My assumption is 5 - 10% gelatin. And processing at 68 F (20C). And using no Dektol or stop bath. These are all critical concerns. Or can be.

    PE
    I use the c.alum for plates. FYI, I mixed my emulsion with food gelatin from grocery, in my country it's very hard to find photography gelatin and even Knox gelatin.

  3. #23
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    Food gelatin contains a lot of additives to preserve it and these can cause sediment to form. This leads to spots on the negatives and low contrast. Filtering the emulsion through a mesh coffee filter can help.

    PE

  4. #24

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    Quote Originally Posted by Photo Engineer View Post
    Food gelatin contains a lot of additives to preserve it and these can cause sediment to form. This leads to spots on the negatives and low contrast. Filtering the emulsion through a mesh coffee filter can help.

    PE
    PE,
    Yes. I already mixed 3 batch of emulsion and still the result low contrast but my option now go for Bromoil print. A bit hard to get perfect print. Any idea?
    Here the sample:-
    Attached Thumbnails Attached Thumbnails img039 copy.jpg  

  5. #25
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    Without knowing the formula, I think you need better gelatin. But, there may be other problems.

    PE

  6. #26

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    I'm using this formula:-
    Solution A
    - Gelatin from the grocery store 10g
    - Potassium Bromide 8g
    - Distilled Water 62.5ml
    Add the gelatin to the water and allow to swell. Put the container (preferably
    stainless steel, like a 2-reel still film developing tank) into a water bath and raise the
    temperature to 50°C. Add the potassium bromide and stir or swirll continuously
    until both ingredients are dissolved.

    Solution B
    - Silver Nitrate 10g
    - Distilled Water 62.5ml
    Dissolve the silver nitrate in the water by stirring or swirling, again, in a stainless steel
    container (a processing can for 35mm still film is ideal), and raise it's temperature to 40°C
    in a water bath.

    Is that problem if I use different temperature and maybe more 50°C for Solution A and less temperature for Solution B?

  7. #27
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    sagafiore,

    That's a lovely image. Is it a bromoil from your dry plate? If so, what is the improvement you'd like to see?

    Regarding your recipe. It's really not complete. It has the same problem as the recipe Martina is using from the book "Silver Gelatin". The ripening step is missing. Making an emulsion is, in every way, the same thing as cooking. If you were baking a loaf of bread, you would know that you need to do more than mix the flour, salt, yeast, and water in a pan and throw it in the oven. You'd understand that you need to raise the dough first, and that time and temperature matter. Grape juice takes time to become wine. Milk to cheese, etc, etc.

    By coating the emulsion before it has had time grow and mature its grains, you very likely won't be getting the emulsion you want.

    After the precipitation step (adding the silver nitrate solution to the salted gelatin, aka "addition"), let the emulsion sit in a ~50C waterbath for 30-60 minutes, stirring gently for 10 seconds every 10 minutes. Then, cool to coating temperature. Take careful notes of when you did what, at what temperature. Time, and temperature, and agitation are the ripening variables. Too much time or temperature will start to fog the emulsion. Too little of either will all but guarantee a dull emulsion. Start on the conservative side, and with each subsequent emulsion making session, increase the time and/or temperature. At some point, you won't like the emulsion, and you'll know that the last recipe specifics were the right ones (for you.)

    Also, you don't spell out how you add your silver solution to the salted gelatin. The precipitation method is an emulsion characteristic variable. Additional ingredients can also be considered variables. A little potassium iodide does wonders for a bromide emulsion.

    When someone starts talking about 'variables' and 'taking notes', it's easy to think that means making an emulsion is hard. NOT SO! . It's no more or less hard than baking a loaf of bread. No one would argue that baking is too complicated just because it's important to get the ingredients, times, and temperatures correct.

    One more question: Are you washing your emulsion? If not, you might (probably will) see the emulsion making leftovers crystallize out on your plates. (You don't need to wash an emulsion if you are coating on paper because the paper absorbs the chemical byproducts.)
    Last edited by dwross; 02-20-2014 at 10:46 AM. Click to view previous post history. Reason: thought of another question
    www.thelightfarm.com
    Dedicated to Handmade Silver Gelatin Paper, Film, and Dry Plates.

  8. #28
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    Denise has pretty much spelled it out.

    The addition time of Silver Nitrate to salted Gelatin can control contrast, and an unwashed emulsion tends to have a lower contrast than a washed emulsion. You see, the leftover halide, besides forming crystals, can act as a restrainer. So washing a plate or film emulsion is a necessity.

    PE

  9. #29

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    dwross ,

    That's a lovely image. Is it a bromoil from your dry plate? If so, what is the improvement you'd like to see?
    First of all I coated to paper then the result I saw low contrast so I move my prints to Bromoil because I dont like the contrast.

    Regarding your recipe. It's really not complete. It has the same problem as the recipe Martina is using from the book "Silver Gelatin". The ripening step is missing. Making an emulsion is, in every way, the same thing as cooking. If you were baking a loaf of bread, you would know that you need to do more than mix the flour, salt, yeast, and water in a pan and throw it in the oven. You'd understand that you need to raise the dough first, and that time and temperature matter. Grape juice takes time to become wine. Milk to cheese, etc, etc.
    Yes, off course I'm followed the step from "silver gelatin" book for unwashed emulsion.

    By coating the emulsion before it has had time grow and mature its grains, you very likely won't be getting the emulsion you want.
    Noted

    After the precipitation step (adding the silver nitrate solution to the salted gelatin, aka "addition"), let the emulsion sit in a ~50C waterbath for 30-60 minutes, stirring gently for 10 seconds every 10 minutes. Then, cool to coating temperature. Take careful notes of when you did what, at what temperature. Time, and temperature, and agitation are the ripening variables. Too much time or temperature will start to fog the emulsion. Too little of either will all but guarantee a dull emulsion. Start on the conservative side, and with each subsequent emulsion making session, increase the time and/or temperature. At some point, you won't like the emulsion, and you'll know that the last recipe specifics were the right ones (for you.)
    I don't take a note before this and I will do for next batch.

    Also, you don't spell out how you add your silver solution to the salted gelatin. The precipitation method is an emulsion characteristic variable. Additional ingredients can also be considered variables. A little potassium iodide does wonders for a bromide emulsion.
    As I mention on top, I'm followed the 'silver gelatin' book process and maybe the temperature a bit wrong.
    How to add the potassium iodide in this unwashed emulsion?
    'Silver Gelatin' book did not mention for this unwashed emulsion
    May I know the reason and function for adding potassium iodide?


    When someone starts talking about 'variables' and 'taking notes', it's easy to think that means making an emulsion is hard. NOT SO! . It's no more or less hard than baking a loaf of bread. No one would argue that baking is too complicated just because it's important to get the ingredients, times, and temperatures correct.
    "thank you for suggestion"

    One more question: Are you washing your emulsion? If not, you might (probably will) see the emulsion making leftovers crystallize out on your plates. (You don't need to wash an emulsion if you are coating on paper because the paper absorbs the chemical byproducts.)
    No I'm not washing the emulsion.


    Thank you in advance.

  10. #30
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    Interesting post. Yes, making an emulsion is not hard. But those in the book "Silver Gelatin" which I think is an excellent reference are untested and there are many misprints there. So, tread carefully.

    It is not generally known, but up until the time of RC paper, most paper emulsions were unwashed. The paper itself absorbed the salts and prevented crystallization. Film emulsions MUST be washed or you get a tacky surface with lots of crystals.

    KI is added to increase speed and contrast. It can be added to the salted gelatin or after the wash step. THIS depends on the desired effect. Other addenda are also useful such as Rhodium Chloride and Cadmium Nitrate. It depends on emulsion type.\

    This just reinforces the comments in the above post.

    PE

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