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  1. #1

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    Help please - problems with coating plates

    O.K. folks,

    This is a plea for help after my first disastrous attempt at plate coating using a dummy emulsion… :o

    I cleaned a dozen old plates by immersing them in hot caustic soda.

    My emulsion formula uses 15g of gelatine and it says that when complete ‘the final quantity should be around 240ml’. So, I made a dummy emulsion using 7g of gelatine in about 100ml of water. I added a little red food dye & also added a teaspoon of table salt, thinking this would simulate the salts in the real emulsion.
    Duh! It was of course a daft idea as it behaves like an unwashed emulsion and the salt crystallises out on the surface. That’s what comes of trying to be too clever…

    I melted the gelatine in demineralised water at 40 degrees C with 4 ml of chrome Alum solution (which was 1g of Chrome Alum per 100ml).

    I then tried pouring the plates. I won’t go into the full gory details, other than to say it was a total disaster! I clearly have a lot to learn. I have had three attempts now and have solved some of my own problems, but here are the ones that I am still struggling with:

    1. No matter how well I clean the plates, the emulsion doesn’t flow evenly. Sometimes it decides to leave an ‘islands’ where it just will not run. This can be overcome by pouring plenty of emulsion right in the middle of the area it doesn’t like, but usually results in excess emulsion spilling over the edges and going everywhere.
    Any ideas how to make the emulsion flow evenly over the whole plate?

    2. What should the coating temperature be? I found that at 40 degrees the emulsion was very thin and watery and difficult to keep on the plate. It gave a very thin coating, possibly too thin at the corner opposite to where the excess was poured off. It easily spilled over the edges and went everywhere.

    At 25 degrees it was like treacle. Much easier to handle, thicker coat, less waste, but much more likely to refuse to flow over the whole surface leaving lots of areas not covered and the side where the surplus is tipped into the bottle ends up three times thicker than the opposite corner.

    3. Always, ALWAYS the corner where the excess is tipped off ends up with a drip that runs underneath and glues the plate to the slab. Any attempt to wipe it ends in tears as the plate is just resting on my fingertips…

    4. The original professional coatings on the plates were incredibly tough and difficult to remove. My coatings are extremely fragile. I was able to remove them completely by just placing in lukewarm water and gently rubbing. I do not believe they would stand up to normal processing. I thought that maybe the concentration of chrome alum was too low so I double the quantity to 8ml. This didn’t seem to make the emulsion any harder and my last attempt may even have been softer. I could easily leave my fingerprint on the surface after 24 hours drying.

    I am now concerned about the gelatine. It was bought from a photographic supplier as ‘photographic grade gelatine’ – but I do not know it’s bloom value.
    Is there any way to tell?
    The supplier said that it came from Kentmere who I emailed for the spec, but they didn’t reply.
    Could the gelatine be too soft? Or is the concentration of gelatine too low?
    Or is there a problem with the amount of chrome alum?
    Or are the additives in the food colouring to blame?
    It contains glycerin and citric acid, although I only added a few drops.
    Or maybe the table salt?

    I’m going to try just gelatine and water next at different concentrations.

    Any answers or advice will be most gratefully received!

    Steve

  2. #2
    ben-s's Avatar
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    Well Steve, I wouldn't be too disheartened - You've had problems, but at least you're part way to solving them!
    I'm afraid I don't know why things are falling off the plates, but I guess it has something to do with the salt.
    AFAIK, the hardener takes some time to kick in fully, so you might want to wait a few days before trying a test to destruction...

    PE has mentioned the use of some kind of surfactant to aid spreading, although I can't remember what it was.
    Edit: Photo-flo is mentioned several times - you could try a few different wetting agents and see what happens
    Last edited by ben-s; 08-22-2007 at 03:07 AM. Click to view previous post history.
    Lens caps and cable releases can become invisible at will. :D

  3. #3
    rwyoung's Avatar
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    You might want to google around for wet-plate collodion technique web sites for some ideas. I realize you are working toward a dry-plate but I'd be willing to bet a lot of the techinque for plate pouring is the same.

    Scrubbing the plate surface with Rhottenstone (calcium carbonate + Everclear) seems to be the next best thing to Glasswax. I've played with BonAmi clenser + alcohol too.

    Some wet-plate workers sub the edges of the plate with a little albumen. And all of them knock down the edges with a file or stone first. I've seen (and done) people use the back of their pouring hand or a folded up paper towel palmed in their pouring hand to dab away the excess at the back of the pour-off corner. The pour-off corner will probably always be a little on the thick side for any hand-poured coating.

    And finally, while not the same was what you are going to pour, one recomended practice pouring fluid for wet-plate collodion is Karo syrup...
    Don't sweat the petty things and don't pet the sweaty things! http://rwyoung.wordpress.com

  4. #4
    smieglitz's Avatar
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    Have you tried warming the plate so the gelatin doesn't congeal as rapidly as it flows over the surface? Keeping both the glass and gelatin emulsion warm should give you a little extra time to coat evenly.

    I'd echo the use of CaCO3 (whiting or rottenstone) mixed with a little 190 proof Everclear to clean/polish the plate before coating. I've also had luck with wetplate using a final weak acetic acid (~10%) rinse and drying with clean towels before coating collodion plates. And yes, albumen edge subbing and sanding the edge does help the emulsion adhere.

    Between pouring the pancake in the center and pouring off the corner I try to get the coating done within 5 seconds or less for a full-plate. How long is your pour taking?

    Joe

  5. #5

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    Thanks for the feedback, chaps.

    I will try the rottenstone / Everclear idea.

    Actually, I've no idea where to get rottenstone, but I have got some precipitated chalk, which I believe to be MgCO3 which hopefully should do the same thing.

    I didn't know what Everclear was... so I googled and now know I need to mix it with kool-aid and apparently I can then get hammered with a minimal hangover.
    :o

    I had to google kool-aid as well, and now know it is an album by Big Audio Dynamite... Hmmmm.

    Perhaps I'll try a paste of Ethanol and Chalk


    Between pouring the pancake in the center and pouring off the corner I try to get the coating done within 5 seconds or less for a full-plate. How long is your pour taking?
    About half that time unless i am fiddling about trying to get an awkward bit to fill with emulsion - but my plates are much smaller.

    Steve

  6. #6
    rwyoung's Avatar
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    Everclear vs. 95% ethel alcohol, they can be swapped no problem for the Rottenstone formula.

    One suggestion is to mix it up in a squeeze bottle (mustard bottle). Then when you need to apply it, you shake it up first. It WILL settle. Also, if you aren't going to be using the bottle for more than a few days, use some plastic wrap under the lid (catch the threads of the lid) to seal the bottle.
    Don't sweat the petty things and don't pet the sweaty things! http://rwyoung.wordpress.com

  7. #7

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    Rottenstone is a fine abrasive used in wood finishing (among other things, obviously).
    Here's one source located on your side of the pond.
    http://www.craft-supplies.co.uk/cgi-bin/psProdDet.cgi/LW333||polish~@c~@b|40|user|1,0,0,1|94|

    I've only done business with the US analog to this company, but I know they've been in business for a good while.

  8. #8

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    Hi,

    You can use whiting (hardware shops used to sell it) people mix it with water and coat greenhouse windows with it so I suppose garden centres might stock it. You can also use tripoli powder (from places where they make violins - used as a fine finishing agent on the lacquer). Any alcohol that evaporates quickly will do. You can even get away with distilled water (providing greasy marks have been removed from the glass first) or weak ammonia.

    Rottenstone and Tripoli are available from some better artists suppliers.

    Regards,
    Neil.

    PS: Joe's idea of keeping the plate warm is a good one!

  9. #9
    Photo Engineer's Avatar
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    I suggest that cleaning is not your problem.

    I have posted a complete set of pictures of a world class expert coating glass plates. It is here on APUG in another thread with comments and pictures including a jpg of the negative and a print.

    All hand made glass plates have run back on the reverse side of one corner.

    I am no expert by any means but here are tips from the expert.

    1. Gelatin should be 8% - 10%, no greater. It can be less if you can handle it.
    2. Temp should be about 40 C.
    3. Gelatin should be 250 bloom.
    4. The plate should be pre-warmed.
    5. The emulsion should contain either a surfactant or some Everclear to help it spread.
    6. Breathe gently on the plate in your hand before pouring the gelatin.
    7. A real emulsion is thinner than the same plain gelatin mixture.
    8. Dyes or colorants in gelatin tend to thicken it up or change it significantly due to their being sulfonates.

    And, don't pour on so much or tip so far that it begins dripping off your elbow.

    PE

  10. #10

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    Thanks very much for the suggestions,

    Quote Originally Posted by Photo Engineer View Post
    I have posted a complete set of pictures of a world class expert coating glass plates. It is here on APUG in another thread with comments and pictures including a jpg of the negative and a print.
    Yes, I've studied the pictures of Mark Osterman carefully and I am attempting, in my own clumsy way, to copy what he is doing. It is much harder that it looks! But I'm getting there, albeit messily...

    I think my biggest problem is the consistency and the refusal to flow and set properly of the emulsion I'm pouring.

    I'm going to have another session tommorrow where I will put all of the above suggestions into practice and leave out the food colouring...


    Steve
    Last edited by steven_e007; 08-24-2007 at 02:45 AM. Click to view previous post history.

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