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  1. #21

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    David,

    Was this a sheet of hand-made paper or commercial? Try to fix as many variables as possible with the experiment to see what is influencing your print. How about taking a sheet of paper and coating half of it with the vinegar mix (e.g. the top half) and when it is dry, coat with the cyanotype mixture. Then place the negative, but cover say the left half of the image with a few layers of kitchen foil to make sure it is dark. Expose the image for the shorter time you have used in the past, then remove the foil and expose the extra time needed to match your last exposure.

    You will now have 4 experiments on one sheet of paper; all of which use exactly the same paper, exactly the same cyanotype mix and also are all washed out for the same time in the same pH water. If the two vinegar quadrants show the mottling effect then the pre-wash is the culprit. If all quadrants show it, then the paper, the cyanotype mix or the wash water are to blame etc.

    My guess is that it is an interaction between the vinegar and the sizing. If it is handmade paper, there may be some effect of the original size in the paper that has been pulped; if the additional exposure causes the mottling, it may be the old paper size causing a faster response in some areas than others, the effect would be present at the shorter exposure but not as noticeable.. As I mentioned before, I have found that the pH of the paper itself does not seem to make much difference, it is the materials used for sizing that can have a dramatic effect. For example raw gelatine as a size seems good; adding 3% alum is also good and the paper is stronger. Adding 20% alum (not uncommon in some old papers) will make the print turquoise, increase the printing speed by almost a stop (hence why it could be an old size issue) and you may never wash out the yellow stain.

    Do you know what the paper has been sized with? You previously mentioned arrowroot; I found using a coat of boiled flour as a final starch size on top of the gelatine makes coating the paper an absolute dream and the blue goes really dark, however the paper curls really badly and while trying to get it flat, the size can crack and flake off.

    Best regards,

    Evan

  2. #22

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    Thanks for all the ideas / information Evan; this particular paper is commercial stuff and I'm not sure what it is sized with to be honest. I've just coated another two sheets, but this time I added 1% citric acid to the sensitised solution as I recall reading somewhere that it can help with dealing with this sort of issue.

    Just in case anyone else is reading this, it just be worth mentioning that the citric acid powder must not be added directly to the sensitised solution. I mixed 4g of citric acid to 10ml of distilled water, then added 0.5ml of this to 55ml of sensitised solution, before brushing it on the paper.

    I'll see how this goes over the weekend. By the way, the arrowroot was what I am intending to use this weekend if I get a chance to make some more hand-made paper. That's actually where I want to be - printing cyanotypes on my own paper.

    Thank you,
    David.
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  3. #23

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    Hey
    after develloping (water) add some drops of a diluted 3% peroxyde solution (who is harmless) but this will oxidise the rest of the Fe in a nice dark blue Fe complex much more stable

    jm

  4. #24

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    That's what I've been doing anyway - after washing, I put some normal household bleach into a litre of water and pour it over the paper; you can watch the image darken down as you pour it over. However, I believe that you would achieve the same thing just by leaving it for a few days to oxidise normally.

    I've just tried toning the blotchy image - and it actually reduced the obvious blotches I'll scan it in when it's dry and add some details too...
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  5. #25

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    As promised... this is the same blotchy cyanotype after toning in tannic acid & sodium carbonate. It seems to have improved the contrast too, which I'm rather happy about!

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  6. #26

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    David,

    Did the cyanotype look blotchy when it came out of the developing rinse and before you enhanced the blue with the bleach wash? It may be worth checking to see if it is just hydrogen peroxide in the bleach as any other additives may have an unknown effect on the image. I just leave my cyanotypes to oxidise naturally.

    I like the toning you have applied; I do not have tannic acid to hand so I use teabags. I find that normal black tea stains my handmade paper really quite dark, whereas green tea is far better and only tints the paper slightly whilst still giving a good change in the blue colour.

    Best regards,

    Evan

  7. #27

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    The cyanotype looked blotchy before it got washed; so at the end of development / exposure.

    The toning completely changes the feel of the image, and it seems a bit odd calling it a 'cyanotype' when there's not a hint of blue anywhere

    I popped into a home-brew store on my way home from work and bought a small container of 'Wine Tannin' to do the toning with. It was really quick: 20 seconds in the tannic acid, and a minute or so in the sodium carbonate.

    Cheers,
    David.
    Creative Image Maker e-magazine is back! Find out more at http://creativeimagemaker.blogspot.com

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  8. #28

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    Whoa!? I detect several errors that should be corrected:

    - Cyanotypes are pretty consistent as long as one is able to control exposure (= which is the absolute amnt. of useful energy the emulsion gets) AND (both the environment's and the paper's) humidity levels. I've gone thru several batches of several papers - such as COT 320, Masa, Fabriano Artistico (acidified) and Fabriano 5 to name few... - w/o noticing any inconsistencies. When you're printing with an artificial lightsource (= having full control over the amnt. of energy that reaches the emulsion, unlike printing under sun), keeping everything else constant, humidity is the single most important variable in determining exposure times. And please note that RH % values aren't much informative in determining "the absolute water content in air and paper" (which is "the" crucial parameter), as long as they're paired with temperature. In other words; 50% RH will require different exposure times while working at 18C and 25C, for instance... My solution to that problem was to print on bone dry paper. Thanks to that method, I can get consistent exposures/results both in winter and summer, regardless of the RH levels, but with the expense of speed loss. (Because emulsion speed is directly proportional with the moisture level in the paper...)

    - More later; I have to go now...

    Regards,
    Loris.

  9. #29

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    I continue from where I left:

    - Sizing is very important indeed. First of all, you need a right amnt. of sizing to have nice cyanotypes; if there's more sizing than what is needed, you'll loose some density because cyanotype needs to be "in" the paper not over it (the image / prussian blue particles should be trapped "in" the paper's fibers), and especially traditional cyanotype is notorious for not wanting to get in the paper (unlike new cyanotype). OTOH, if there's less sizing than what is needed then the image looses snap and/or (most importantly) the paper disintegrates and/or gets damaged and/or handling gets much harder during processing stages. BOTH alkali paper or sizing (and mounting / storage materials) are detrimental to the process; in terms of yellow staining (because of formation of iron hydroxide) and fading of the image. For instance if you print cyanotype on non neutralized Fabriano Artistico (which is a paper that has a substantial amnt. of calcium carbonate - an alkaline compound - "in" it as a buffer, in order to increase longevity) you'll experience longer than normal exposure times and a weaker image - which may get even weaker with time.

    - Bleach isn't the best oxidizing agent for cyanotype processing because it's an alkaline solution. (See above.) 5-10 ml of ordinary household hydrogen peroxide to a liter is the best tool for the purpose of quickly oxidizing the image to full density without having to wait (at least) 12 - 24 hours.

    BTW, David, your image is weak and from what I see, I infer you need some more exposure. (Since there aren't any strong darks under the negative.) IME, the best negative for traditional cyanotype has to have a density range around log 1.4 - 1.5.

    - You DEFINITELY need to have solarized portions under the negative as an indication of correct exposure and to able to get maximum print density. (I mean if you have true blacks in the original scene...) If you don't see any solarized (to slate gray) portions under the negative (right after exposure, before processing) then you're definitely underexposing the negative. Washing steps and oxidation bath will take care of the solarization and will render that parts of the print as maximum density...

    Regards,
    Loris.
    Last edited by Loris Medici; 01-21-2010 at 01:48 AM. Click to view previous post history. Reason: Fixed few typos and added a note about solarization.

  10. #30

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    I agree with Loris that humidity can have very pronounced effects with some paper/size combinations. I always dry my paper with a hair-drier to try to remove as much water as possible.

    I did some tests a while ago where I sized a sheet of (hand-made) paper with bands of different sizings, then coated the sheet of paper with cyanotype mix. I then cut the sheet in half (ie across the bands of sizing); let one piece air dry on a humid day, and hair-dried the other. I then exposed both halves with a step-wedge at the same time. By all the samples having the same base paper pH, same coating mix and same exposure time, I fixed many of the key variables.

    What happened next depended on what sizing has been used, and how it had been dried. All of the test patches looked different when they came out of the contact frame; some had pronounced solarisation (ie seemed more sensitive), some not etc. When developed in water, they all developed differently too; some washing quickly, others with the blue 'floating off' (acrylic gesso as a size). When they dried and had oxidised fully, some of the sizes had very different results for the air dry/ hot dry (eg flour+alum), however with some (pure gelatine for example), there was little discernible difference.

    Best regards,

    Evan

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