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  1. #21

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    Found it!

    I do not recall any direct mention of this being used to produce black and white images
    having contrast differences.


    I have now found the information, so the above comments are no longer valid.
    It is, however, still much later than the material I initailly hinted at... and so the search continues for the rest of the story.

    Thanks for pushing my buttons and making me go through my files!

    Since it is too late to get much sleep now, I am off to pick up a new arm and leg... uh, i mean electrodes. They are sure expensive enough! (up til now I have been reading the analog needle type under red safelight - you know where you line up the shiny part with its shadow... not an easy task in a darklab!
    Anyway, next comes automation... so this newer digital work horse will be worth it... I hope.

    Unfortunately, my ions are still metered analogistically
    tosleepieetotalk....

  2. #22
    AgX
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    PE, Ryuji thank you both so much for those informations!

    I was aware of the technical shortcomings of the industry of that time.

    Well, I admit blending emulsions was not a good idea, due to the inherent blue absobtion, which would needed a kind of desensitation of one. But my other idea was that they could have made two emulsions yielding different gammas, give one an ortho sensitation. Coat the unsensitized, coat a filter layer (which should discolour while processing…) coat the ortho emulsion. Yes, quite a hazzle.
    And I totally forgot about any migration of filter dyes and about the remaining colour of the sensitizer dyes….


    Ryuji,
    I was in the belief that sensitzers had a great adsorbtivity to the halide (keeping aside that problem of substitution by an anti-fogging agent you referred to elsewhere). Thus they won’t migrate. If they would migrate later whilst processing that should not be a problem (in contrast to those colour couplers).
    A problem however would have been if the migrated while coating. But wet/wet coating was not done anyway then.
    Thus there might still be a migration, whilst in stock, of not adsorbed sensitizers still around in the gelatin.
    Was it the latter you were referring to?

  3. #23

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    Adsorption of dye molecules on AgX surface varies a lot depending on the dye. (And this is also true of developing agents, etc.) Good ones adsorb quite well. But I am not sure (without doing a bit of research) if good ones were in common use, or at least available in commercial quantity c. 1912.

    Another reason why variable contrast emulsion was not very good until 1970s (at least) has probably because it is not very easy to make a high contrast emulsion using single jet method (which was described by AGFA people in 1950s, but it remained only within the research community for another decade or two) and the methods of variable contrast emulsion can only lower the contrast, not boost, beyond the effect you would get from a larger coating weight of one of the emulsions. Now we can make monodisperse emulsion using double jet, and a single emulsion (without any special development technique) can be made fairly high contrast. So it makes more sense to start with these and vary the contrast by lowering it.

  4. #24
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    AgX;

    I have mentioned elsewhere that I have, within my reach, the ability to make a variable contrast Azo type paper. It uses all of the methods I've mentioned here, including the base soluable sensitizing dye which I have a supply of. It is doable because the Azo type emulsion, which is single jet, can be made in contrast grades from about 1 - 4. This is also doable with the AgBr enlarging emulsion that I posted earlier, although I have not done significant work on it yet.

    It is also the reason I have been working on 2 layer coating with my blades so that I can have an alternalte method of doing this if blending does not work. Of course, the dual coating is also intended for color work sometime in the future.

    I am in doubts as to whether I should proceed though as there did not seem much interest in VC contact paper, and VC enlarging papers are still available. So, right now a lot of other things are undergoing development and these projects (including color) are on the back burner.

    I should also add that I have never seen a modern tinted VC enlarging paper. This indicates that there is no significant blue absorbing dye, and no huge level of sensitizing dye to discolor the paper. Much of this is achieved by using a super-sensitizer, which is not a dye, but a colorless additive which boosts dye sensitivity manyfold. Therefore, VC papers are white. This also indicates that the silver halide is high in chloride and low in bromide and iodide which impart a yellowish cast to the raw paper. Of course, the low silver level in modern papers will repress any visual impact of color as well.

    PE

  5. #25

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    Ray - what kind of electrodes are you getting? I've recently bought a digital pH/mV meter and a pH electrode as well. What are you using?

  6. #26

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    Quote Originally Posted by Kirk Keyes View Post
    Ray - what kind of electrodes are you getting? I've recently bought a digital pH/mV meter and a pH electrode as well. What are you using?
    They are 3 seperate type electrodes, not 2or3 in one.
    pH range 0-14
    0-100 degree C.
    that require a minimimum of 20 mL

    Now I am starting to have second thoughts...I wonder if I should have tried something new this time... I don't know... I did pick them up today, but I find I'm still looking at design specs for other models.... Monday I will be hearing from the mfg. anyway maybe I will exchange it...
    there are +es and -es to either choice.

    How about yours?

    Ray

  7. #27

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    Ray -

    From my lab experience with everything from very clean waters to really scuzzy samples, I highly recommend Thermo/Orion Ross-type electrodes. They seem to last a long time and are pretty stable. Much more than regular old fashioned general use electrodes I've used in the past. I see Ryuji suggests using Ross electrodes on his web site as well. The Orion 81-02 electrode should be a good one.

    Here's a nice guide to Orion Ross electrodes:
    http://www.boekel.ca/catalog/en/ph_e...es_orion2.html

    That said, as I wanted to stay somewhat on budget, I bought a Mettler INLAB 413 pH triode electrode with a built-in temp probe. Unfortunately, the connector on the Mettler temp does not mate with my Orion meter... But it was only $40 and new in box.

    I see right now there is an Orion Ross electrode on ebay:
    http://cgi.ebay.com/NEW-THERMO-ORION...QQcmdZViewItem

    Watch out as there is a Ross half-cell and for sale as well, and the person selling the above linked electrode also has an electrode that says Ross in the title, but it is not if you look at the listing... it's an Orion perPhect pH electrode with has an Ag/AgCl junction, not the best for photographic uses, but a good overall electrode for other uses.

    Something like this would be a good choice. It's a "heavy duty" model, which one may want if they are not used to handling pH electrodes, or if they are clumbsy...

    For people reading this that are looking for bargains, absolutely do not waste your time with a used lab elctrode. All the labs I've been in, when an electrode is going bad or getting old and response is sluggish, they disconnect the electrode, and set it on the counter behind the pH meter. And then is sits there, sometimes for a long time, getting dry and crusty. And not good to use after that. And then there's the ones that have cracks in the sensing bulb. Buy something new when getting a pH electrode.

    Also, make sure you get one that is a "combination" electrode. Not a "half-cell" electrode. You want a combination as it has the half-cell reference electrode build into the body of the pH electrode - so it's really two electrode in one housing. You want that. Also, if you can get a temp probe built-in as well, that's really nice. Those electrodes usually have "triode" in the name to let you know that it's got pH, half-cell reference, and temp all in one unit.

    What have you been using and what are your looking at?

  8. #28
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    Ray, Kirk;

    I suggest looking here:

    http://hannainst.com/usa/subcat.cfm?...FQKAHgodmmGNxQ

    You used mine in the workshop Kirk.

    PE

  9. #29

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    Yeah, it's a nice meter and certainly friendly to the budget, but sometimes it's nice to have something that is more versatile.

  10. #30

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    Quote Originally Posted by Kirk Keyes View Post
    Ray -

    ...there is a Ross half-cell and for sale as well, and the person selling the above linked electrode also has an electrode that says Ross in the title, but it is not if you look at the listing... it's an Orion perPhect pH electrode with has an Ag/AgCl junction, not the best for photographic uses, but a good overall electrode for other uses.
    Kirk,

    Since the Ross reference is said to be neither Ag nor Hg based, what is it?

    Ray

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