Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,735   Posts: 1,515,483   Online: 1063
      
Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 22
  1. #11
    Joe Lipka's Avatar
    Join Date
    Sep 2002
    Location
    Cary, North Carolina
    Shooter
    4x5 Format
    Posts
    808
    Do it all the time for step wedges used in testing Pt/Pd prints. Used it on FB silver paper, too. Didn't work for me when I was doing RC "paper". The emulsion boiled.
    A New Project! Transformations 02/02/2014

    www.joelipkaphoto.com

    250+ posts and still blogging! "Postcards from the Creative Journey"

    http://blog.joelipkaphoto.com/

  2. #12
    donbga's Avatar
    Join Date
    Nov 2003
    Shooter
    Large Format Pan
    Posts
    2,053
    Quote Originally Posted by blaughn
    recommended for production prints.
    What are production prints?

    Don Bryant

  3. #13

    Join Date
    Mar 2005
    Location
    Minnesota
    Shooter
    4x5 Format
    Posts
    415
    Images
    11
    These are the prints you are producing for display of inventory - the finished product.

  4. #14

    Join Date
    Aug 2005
    Shooter
    Multi Format
    Posts
    1
    I use a microwave to test prints, I microwave them for 30 secs let them cool a bit and then do another 15-30 depending on the size of the print. I then let them sit for a few minutes for the remainder of any moisture to evaporate. It works really well, so far I cannot tell much of a difference in the final air dryed print.

  5. #15
    PeterB's Avatar
    Join Date
    Apr 2005
    Location
    Sydney, Australia.
    Shooter
    Medium Format
    Posts
    596
    Quote Originally Posted by Photo Engineer
    The environment around the silver filaments in the print is changed on a micro scale during microwaving. This has a subtle effect on the tone as noted above. IDK how bad or good it is, but I know it takes place.
    PE
    What change are you talking about? How do you know that it takes place?

    For microwaves to actually induce an electric field (AC current) in the silver metal, the length of the metal should be optimally 1/4 the wavelength of the microwaves (approx 12cm/4=3cm). The dimensions of any 'continuous' length of silver metal in the photo paper is much less than this. In fact the individual and unconnected silver halide crystals which then develop to form filamentary silver are tiny.

    regards
    Peter

  6. #16
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,869
    Images
    65
    Quote Originally Posted by PeterB
    What change are you talking about? How do you know that it takes place?

    For microwaves to actually induce an electric field (AC current) in the silver metal, the length of the metal should be optimally 1/4 the wavelength of the microwaves (approx 12cm/4=3cm). The dimensions of any 'continuous' length of silver metal in the photo paper is much less than this. In fact the individual and unconnected silver halide crystals which then develop to form filamentary silver are tiny.

    regards
    Peter
    Peter, although an individual silver halide crystal in a B&W paper may be small, on the order of 0.2microns on a side assuming a cube of AgCl, the filament that is formed may indeed be quite long. This is assuming filimentary silver formation during development as opposed to tabular.

    There are ample photomicrographs of the filaments that form in the literature that I don't feel I have to post one here, but I do believe that they can approach a considerable length, but whether they can react with the shorter wave microwaves IDK. I doubt that anyone has 'unravelled' one of the filaments that form to actually measure its length.

    But, as you say, the operative word is 'optimally' meaning that the highest statistical probability is if the wavelength is as you say, but that does not rule out induced current in shorter or longer filaments. (does it?)

    In any event, I have not personally tried it, as I was dissuaded from using a microwave by my co-workers when I suggested it as a very 'green' researcher many years ago. As a result, no one I knew every used microwaves to dry photo products in KRL. Not even color products which contain no silver when finally processed. (This latter was interesting as I thought of it while writing this reply)

    Now, I may be wrong, and we may have missed something, but I had very pursuading counter arguments made to me by very respected individuals. So, for what it is worth that is the best I can say. I was told it was a 'bad idea' to use microwaves to dry a print or any photo product. Microwaves were never used to dry coatings in a coating machine, but if it were possible that would have been an ideal method of drying a coating.

    In a reply above, someone comments on melting RC prints using a microwave. Heat effects in a developed image would be more evident in RC products due to the relatively low melting point of RC. So, perhaps this was a manifestation of what I believe to be taking place. Also, the change in tone described earlier may be related to this. IDK.

    It may just be that it has nothing to do with the silver itself, but rather a vesicular effect from the micro bubbles formed if you boil water in your wet print causing some sort of translucency. There are many imponderables here that were brought to my attention those many years ago by some very respected fellow engineers with years of experience.

    Final word, you do what you wish, and I do what I wish in my darkroom. I offer only what I have been told in this instance having never tested it personally. I was advised never to try it. I never gave it another thought as we all used hot air drying.

    An added comment. IIRC, it was shown somewhere that microwaving unprocessed photo products had an effect on the latent image. If true, I wonder why? (While writing this, I remembered something regarding this from a publication many years ago and related this to the fact that we never use microwaves to dry coatings) So, make of it what you wish.

    PE

  7. #17
    PeterB's Avatar
    Join Date
    Apr 2005
    Location
    Sydney, Australia.
    Shooter
    Medium Format
    Posts
    596
    PE, I'm not doubting the wisdom of your respected colleagues, my concern was that your proposed mechanism of the paper being "changed on a micro scale" (due to electric currents in the metallic silver inducing heating) has no theoretical basis. I believe that the heating effects are solely due to the water (and any other polar molecules in the paper) heating up.

    I think that a good reason not to dry prints in a microwave is that the uneven heating effects would heat some areas of the paper to excessively high temps. I tried drying an RC print the other day, and sure enough the corners curled up and these curled bits took on a more glossy appearance where I suspect some areas had melted. The problem could be reduced by lowering the power, but even so, some bits of the print would still receive a greater heating effect than other bits.

    The rest of my reply gets into the details.


    Quote Originally Posted by Photo Engineer
    Peter, although an individual silver halide crystal in a B&W paper may be small, on the order of 0.2microns on a side assuming a cube of AgCl, the filament that is formed may indeed be quite long. This is assuming filimentary silver formation during development as opposed to tabular.
    It is the two dimensional 'length' of the filament that is important here. As an example, if I take a telescopic FM radio antenna say 1m long (assume it is very thin for the sake of discussion), and crumple the antenna up into a small cube with a side of only 1mm, then the antenna will be useless if we want it to receive the intended FM radio waves.

    Quote Originally Posted by Photo Engineer
    But, as you say, the operative word is 'optimally' meaning that the highest statistical probability is if the wavelength is as you say, but that does not rule out induced current in shorter or longer filaments. (does it?)
    Technically it doesn't rule it out, but the current's magnitude will be SO small as to probably be but a few more electrons above the noise floor ! I could go and look up the maths, but we'd be talking pico, no, maybe femto-amps for sure!
    The wavelengths emitted by the magnetron oscillator will have a very narrow gaussian distribution centred around the centre frequency of f=2450MHz. This is the idea behind an oscillator - they have high Q's and thus low bandwidth (i.e. spectral spread). FWIW, the frequency for which 0.2microns is a 1/4 wavelength is f=2500GHz. This is 3 orders of magnitude higher than the microwave's frequency of operation.



    Now assuming an object is 'the right size' (has at least one of its dimensions approximately a few cm) then :
    Metallic (i.e. conductive) objects in a microwave heat up because the electromagnetic field induces a current of electron flow which dissipates heat due to ohmic (resistive) losses.


    Non conductive objects that contain polar molecules (e.g. H[size=1]2[/size]O) in a microwave, absorb energy (heat up) as a result of dielectric heating.
    Quote Originally Posted by Photo Engineer
    There are ample photomicrographs of the filaments that form in the literature that I don't feel I have to post one here, but I do believe that they can approach a considerable length, but whether they can react with the shorter wave microwaves IDK. I doubt that anyone has 'unravelled' one of the filaments that form to actually measure its length.
    'shorter' doesn't really make sense here. I assume that the filament length (if stretched out) will still be much shorter than 3cm (=1/4 of the microwave's wavelength). OTOH, if you meant there are sufficiently different length microwaves in the oven to be significant at the filament's length, then that isn't the case.
    Quote Originally Posted by Photo Engineer
    Not even color products which contain no silver when finally processed. (This latter was interesting as I thought of it while writing this reply)
    I think the relevance of this latter point supports my notion that it is the water that is heating things up and not the silver.

    Quote Originally Posted by Photo Engineer
    It may just be that it has nothing to do with the silver itself, but rather a vesicular effect from the micro bubbles formed if you boil water in your wet print causing some sort of translucency. There are many imponderables here that were brought to my attention those many years ago by some very respected fellow engineers with years of experience.
    Quite possibly localised heating could cause this, the object would need non-symmetrical or 'pointy' sections on it for this to happen. This is the case with the corners of the paper.

    Quote Originally Posted by Photo Engineer
    An added comment. IIRC, it was shown somewhere that microwaving unprocessed photo products had an effect on the latent image. If true, I wonder why?
    My guess is that this is resulting from a weak dielectric heating effect.

    regards
    Peter
    Last edited by PeterB; 12-11-2005 at 03:14 AM. Click to view previous post history. Reason: deleted blank lines to make more readable

  8. #18

    Join Date
    Oct 2004
    Location
    Fond du Lac, Wisconsin
    Shooter
    Multi Format
    Posts
    1,065
    Images
    39
    I do occasionally microwave test prints with ilford FB paper. I put a piece of paper towel under the print, and my microwave has a rotating platter. It works fine for this, although the prints done this way do look slightly different from non-microwaved prints. In this case the paper gets slightly glossier and the blacks look a little deeper. Nonetheless, I'd never microwave "finished" prints, as I'd be worried about long-term harm.

    Peter de Smidt

  9. #19

    Join Date
    Sep 2005
    Location
    Charlotte, NC
    Shooter
    35mm
    Posts
    44

    microwaving prints

    instead of microwaving prints, or test strips, I learned something recently that works quickly and well --

    lay the prints out between pages of phone books for a couple of minutes -- the paper absorbs the water quickly and doesn't do anything to the prints!

    A good use for recycled phone books, also!


  10. #20
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,869
    Images
    65
    Peter, your very lucid explanation has convinced me that you must be right and I just never gave the subject enough thought. I do have some additional thoughts that I remembered after the last post.

    First, of course there must be an effect based on all of the above posts, and this must be due to something.

    Thinking back on this last evening, I seem to remember a demonstration of microwaving a step wedge of a B&W material and showing a thickness difference and an imagewise change in tone as a function of step. It was as if the image swelled as a function of the amount of silver and changed in tone quality. That is why I relate, in my mind, the effect of microwave on silver, but perhaps it is due to another effect.

    Your comments above taken with my remembrance of the demonstration would have me consider this imagewise effect to be related to water with some relationship to the silver image, but how, I am at a loss to explain. What I do remember reminds me of a relief image (not exactly) that formed imagewise.

    If it were due to water alone, I would expect this effect to be an even distribution, but I am pretty clear in my memory that the effect was imagewise and the comments here seem to indicate some weak correllation as well with an imagewise change.

    Any thoughts?

    Thanks.

    PE

Page 2 of 3 FirstFirst 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin