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  1. #1
    jbl
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    understanding a green/blue cast

    Hi,

    I'm new to color development and have had a few successful rolls now using the Digibase chemicals. With the help of this group, I've actually gotten pretty happy with what I'm getting.

    I developed a roll of Ektar today and noticed a bit of a green/blue cast on the positive scans and I was wondering what I should be learning from it. My process is to scan using Vuescan using the feature where you can lock the color of the film base. In this case, the DNGs generated come into my software at 6500K with +10 magenta on the tint. I found that if I bump the whole roll to 7500K with +30 magenta things seem to look generally better.

    I wondered if this is the result of my technique still being a bit rough or if this is just the tolerance of negatives under mixed light? The shot I'm attaching is under late afternoon sun. Would shooting a frame of a gray card help getting a sense of how far off my color balance is?

    I don't have a lot of experience with C-41 in general, I've done more black-and-white and chrome work, so I'm not sure what to expect.

    Thanks for all the help,

    Jonathan

    Edit: I'm processing using a stainless steel tank, manually agitated. This is the third roll or so that's been processed with this batch of developer.
    Attached Thumbnails Attached Thumbnails 2011_10_Roll_03_Kodak_Ektar_100_34.jpg  
    Last edited by jbl; 10-24-2011 at 12:21 AM. Click to view previous post history. Reason: adding information

  2. #2
    mts
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    Shoot a grey card and the MacBeth color chart until you get your processing and printing/scanning refined. The orange mask should indeed print as grey, but alas it does not contain dyes produced in the color layers, and therefore your processing may well (read that as always does) produce a color difference from neutral grey. With a grey card you can read the difference with a color analyzer, or you can use the scan data as an after-the-fact color analyzer.
    By denying the facts, any paradox can be sustained--Galileo

  3. #3
    Mainecoonmaniac's Avatar
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    I wonder if the cyan cast is from the orange base on the neg? The cast doesn't show on color paper, but might in scans.

  4. #4
    jbl
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    Assuming it's a processing error, is there any way to know if it's due to temperature, agitation or development time?

    -jbl

  5. #5
    mts
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    Agitation in development (3-1/2 minutes) would show as uneven areas in the image. Time affects image density leading to a thin or an overly dense negative. Your scan shows none of these effects. Temperature affects the image in a manner similar to development time, but also affects the characteristic curves in the individual layers leading usually to cross-over that cannot be corrected in printing; viz. you can print mid-tones properly but have off-color in the shadow and highlight portions, or the opposite sorts of effects, you can print shadows or highlights properly and lose the color balance in mid-tones.

    All these types of errors have to be rather severe to produce an unprintable negative. The best advice I can give is to shoot some test images of a grey card and process these. If the orange base appears uniform and proper then you probably don't have any gross contamination of the developer. I would also suggest checking the pH of the developer that should be about 10.1 to 10.2. A developer that is too active, i.e. high pH, will produce too rapid development of the lower layers in the film thereby leading to color shifts. C-41 is in my experience much more forgiving than reversal E-6 processing that can be corrected only by making an internegative or through reversal color printing or as last resort, digital processing. The ability to filter during printing gives you a lot of flexibility in C-41 that isn't nearly as easy in E-6.
    By denying the facts, any paradox can be sustained--Galileo

  6. #6
    jbl
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    Thanks, mts.

    A couple of more questions, I hope that's not a trouble.

    1) I'll shoot some test images of a gray card. What am I looking for there? It should look gray, but is that useful for anything other to set the white point on a scan? Or can I tell by how far it is off of 6500K how I should correct the roll? If the orange mask should be gray, what does a gray card look like?

    2) What can cause the pH to be too high? If developer is not used one-shot, does the pH go up?

    3) For measuring pH, is there a meter you recommend?

    Thanks!

    -jbl

  7. #7

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    Your shot looks fine to me. Vuescan has a tendency to pick color balance for you. And often not very successfully. It also tends to screw up the Ektar most impressively because of the film's high saturation. In this shot, bench makes a wonderful gray card. Click on it to set color balance and you may get a reasonable shot. This jpg color balances just fine for me in an editor.
    By now you know why most of us here don't particularly enjoy hybrid approach :-). Just print this shot under the enlarger and you'll get a beautiful portrait of a snow-white dog. Your model is super cute by the way!

  8. #8

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    Its just your scannersoftware that doesnt doe the job for you. I Have adjusted and color balanced it for you very quick in curves. If you make a quality scan with proper software, the colourcast will disapear.
    Attached Thumbnails Attached Thumbnails 2011_10_Roll_03_Kodak_Ektar_100_34_bal.jpg   2011_10_Roll_03_Kodak_Ektar_100_34.jpg  

  9. #9
    mts
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    1) I'll shoot some test images of a gray card. What am I looking for there? It should look gray, but is that useful for anything other to set the white point on a scan? Or can I tell by how far it is off of 6500K how I should correct the roll? If the orange mask should be gray, what does a gray card look like?

    A portion of the orange mask is "clear" film and can be used as a starting point to set enlarger filtration to yield neutral grey. You can set a color analyzer or scanner to a starting value this way. Initial filtration found this way is going to be close only if the lighting, processing, and film characteristics are entirely correct which they normally are not. If you expose one frame on each roll with an image of the 18% grey card, or something you wish to call neutral grey--cardboard, a painted card, etc.---then you have something to set your filtration to print/scan/analyze as grey and thereby set filtration. DarkMagic demonstrated this quite well by using the bench color as "grey" in the image.

    2) What can cause the pH to be too high? If developer is not used one-shot, does the pH go up?
    Developer pH is normally set at the time it is mixed and should remain nearly constant throughout its usable life. It could be too high if the chemistry is faulty, but would not be expected to increase with age and use since the chemistry is buffered to maintain the proper alkalinity. As a scratch-mix worker I have to adjust the initial pH according to the amount and source for carbonate in the developer. Usually my 38 gm. of pot. carbonate gives me a pH of about 10.3 and I adjust downward with a few ml. of 20% sulfuric acid.

    The pH of bleach and fixer for color processing should be near neutral or slightly acid, say 6.2-6.5 or so. If you get too far out of bounds in these solutions the color dyes formed in development are degraded. I always use a sulfite-containing stop bath with pH set to 6.2 following developer to avoid bleach contamination and possibly staining.


    3) For measuring pH, is there a meter you recommend?
    I believe that you should really have a pH meter and calibration solution available in your darkroom. When using kits it's not normally necessary but a pH meter in the darkroom is in my opinion like seat belts in a vehicle or helmets and gloves on a motorcycle. When something goes wrong or the kit manufacturer changes their formulation you will notice the difference if you measure the pH before using your solutions. The meter made by Hanna is about $30 on e-Bay and its accuracy of +/-.2 units or so is adequate. There are other manufacturers making similar meters for which with proper care the electrode lasts a year or two. You do need a calibration solution that is in-date and lets you set pH 10.0. I have been using distilled water to set the pH 7.0 point and haven't found the need for a more accurate neutral calibration solution.

    Others may wish to comment here concerning general color processing operational procedures.
    By denying the facts, any paradox can be sustained--Galileo

  10. #10
    jbl
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    Thanks so much, everyone. This is tremendously helpful!

    -jbl



 

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