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  1. #1

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    contrast mix with NA2

    I'm printing some d**tal negs, I know, I know this shouldn't be here but it takes forever to get a reply over at hybrid! Anyway its more to do with chemistry. I've been suggested to use Dick Arentz No.2 mixture. How do I prepare this mixture with my bostick and sullivan chemistry? What's the strength on their sodium choroplatinate? I've been using their advice and using 10 drops of F.O, 10 drops pd, one drop pt and 1 drop water. When printing a 31 step tablet im getting a black but nothing in the highlights, so a short exposure scale when I want a long one. Also, the amount they are suggesting leaves quite a lot of excess with the coating rod. Seeing as I'm only using 1 drop of NA2 how can I possibly add a smaller amount to decrease contrast?! Thanks!!

  2. #2

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    The B&S NA2 is 20%...

    A few things first...don't use pt when using NA2. NA2 is only to be used if you're using pd only. You can, of course, use pt + pd together, but then don't use the NA2. Use solution FO #2 for your contrast in that case.

    With a 12 drop formula, as noted above in your post, one drop of NA2 is way too much. You need to dilute the NA2. Get a couple of dropper bottles, take half of the original 20% out and put it into a new bottle and add the same amount of distilled water. This new bottle will now be at 10% solution. Now take half of THAT and put in a fresh bottle along with the same amount of distilled water. This bottle will be at 5%. Now again, take half of the 5% and put in a new bottle with the same amount of dist water. This bottle is at 2.5%. One drop of 2.5% should be all you need for a decent neg made with 12 drops. That's a good amount to use for a 4x5 print...

    Now that being said, you should start with pd, no pt, at first. Keep your FO and pd amounts equal. 6+6, and no NA2. Expose your wedge for the time it takes to merge two steps into black. That is your exposure time. It is your bible. If anything changes in your workflow (paper, neg material, developer, etc) do the step wedge test for basic exposure time again...

    Needless to say, your wedge must be made in the same manner as your negs...and a lot depends on the density of your negs. Your negs must have a high DR and block UV effectively.

  3. #3

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    Ah cheers that's great advice. Wish somebody told me sooner. I've been using single droplets all along, who knows how much I've wasted. Any advice for what to store the diluted pt in? Should I most definately work out my base exposure with pure pd?

  4. #4

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    I'm using 3 small aftershave bottles that ive washed out throughly and dried in the microwave, think there will be any problem with contamination?

  5. #5

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    Whether you calibrate for pure palladium with no restrainer or choose to mix either platinum or Na2 in the mix is a subjective personal decision. Pure palladium is very warm in tone and has a very long toe and shoulder. If you use a mixture high in either platinum or Na2 you will get a more neutral tone with a more straight line toe. And of course there is a wide range in between the two extremes.

    If you like the warm tone of pure palladium but for some reason need to work with negatives that don't have as much contrast you might consider using dichromate, added to the developer, as a restrainer. Dichromate will not change the color as will platinum and Na2.

    Sandy King


    Quote Originally Posted by Jarvman View Post
    Ah cheers that's great advice. Wish somebody told me sooner. I've been using single droplets all along, who knows how much I've wasted. Any advice for what to store the diluted pt in? Should I most definately work out my base exposure with pure pd?
    Last edited by sanking; 03-31-2009 at 02:03 PM. Click to view previous post history.

  6. #6

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    Quote Originally Posted by Jarvman View Post
    Ah cheers that's great advice. Wish somebody told me sooner. I've been using single droplets all along, who knows how much I've wasted. Any advice for what to store the diluted pt in? Should I most definately work out my base exposure with pure pd?
    You mean the diluted NA2, right?

  7. #7

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    Oh yeah sorry

  8. #8
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    Get a copy of Dick's 2nd edition book and look for the tables.
    The easiest way is to get some pipettes and pipette pumps. Its quite easy to mix any mixture from 4x5 up to 20x24 print sizes for those doing real negatives (and extremely easy for calibrated Pictorico negatives).

    Dick calibrates his digital negatives with a 2s or 3s mix. Unpublished work also resulted in a 0.5s mixture.

    One trick for a long printing session is to make up a larger batch of 2s mix, then just measure out enough for a single print. Keeps at least 6-8 hours without a noticable change in contrast.

    and if you must use drops, for NA2 10%, 5%, 2 1/2% mixes - get some B&S brown dropper bottles and droppers (plastic droppers, don't use glass...too variable in drop size). They're the same ones that B&S sells in the kits with 25ml.



 

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