Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,993   Posts: 1,524,243   Online: 1060
      
Results 1 to 10 of 10

Thread: Hand Coating

  1. #1
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,938
    Images
    65

    Hand Coating

    The book "Silver Gelatin" describes a variety of methods of making coatings in the darkroom. Among them are included brush coating (paintbrush and foam brush), dip coating (using a tray of emulsion) and spraying emulsion on the support. Very good examples are shown of all of these. I suggest that those interested get a copy of this book.

    I have found that brush coating almost always leaves brush marks, and foam brushes often cause bubbles to form in the coating. I have gotten very good coatings from both methods though.

    Dip coating is quite good and was used in the early days of manufacturing of photo products.

    Paper is placed, face down in a tray of heated emulsion, and then is lifted out while dragging the face (emulsion) side of the paper over the edge of the tray to scrape off excess emulsion. It can also be lifted out of the tray and allowed to drip off excess emulsion. I have seen this done with good results, but I find that it varies quite a bit and you cannot adjust the amount of emulsion coated on the paper. It is not very good with film.

    Plates are traditionally coated by pouring the emulsion onto a warm plate and then rocking the plate from corner to corner to get an even coating. Excess is poured off back into the container of warm emulsion. I have done this, but have not mastered the technique. Among other things, the plate coating method requires a precise salt, gelatin and surfactant balance to adhere well to the plate during processing. Early plate formulas used ethyl alcohol at high concetrations to assist in spreading the emulsion evenly. Everclear is the only suitable product on todays market, and it is not available in most states.

    In Kodak Research, it was necessary to make small hand coatings routinely. So, a method was developed for film, and another was developed for paper. Basically, it involves the use of a doctor blade modified for the desired support and the blade is moved over the support, rather than having the support move past the blade. There were about 3 designs of doctor blade in use for film (and also for RC paper) and one design in use for baryta or regular paper as well as RC paper.

    In this method, typically, a blade was adjusted to a given undercut or gap and the emulsion was poured onto the support ahead of the blade. Then the blade was moved over the puddle of emulsion and the blade scraped off the excess emulsion and spread it over the remainder of the support.

    Using this method, a 0.005" (5 mil) undercut, will use about 12 ml to coat 1 square foot of emulsion and from this, the amount of silver can be calculated as well as the amount of gelatin. The spread is very even up to 8x10. I am currently working with a prototype 11x14 blade and a prototype 16x20 blade is in production.

    Film and RC blades are very similar, but plain paper blades differ substantially. A plain paper blade can be used with RC, but can cause severe defects with film. A plate coating blade has been made at EK and I have made one to that general design myself.

    I think that very high quality coatings up to 16x20 are possible, but to get that quality the actual coating must be larger than the desired print for the same reason that machine made coatings are larger than the desired final stock. There are startup and ending defects as well as edge defects in every case, so the coating must be longer and wider than the finished material that you desire. For example, and 8x10 is actually 8.25" x 12" to allow for these defects.

    I think that some form of emulsion making and coating is the future of B&W high end art photography, particularly in prints. I have used a variety of paper surfaces, and am surprised at the quality that I get from Watercolor and Velour papers. Just like old times to me!

    I might add that very complex coating blocks with vacuum hold down and heating and cooling were used at EK. I have found ways around this, as the block would be very expensive for the average photographer. Work is progressing and has been posted by one of my students as she comes up to speed. You can see this in my post regarding the update to my workshop if you are interested.

    Hand coating is a real, possible future for the photographic enthusiast interested in silver halide emulsions. In addition, I have coated Cyanotypes and other alternative photo systems using this. The only ones that didn't work are Pt/Pd systems due to oxalates interaction with gelatin. I intend to work this out as well, if at all possible.

    PE

  2. #2
    Dave Wooten's Avatar
    Join Date
    Nov 2004
    Location
    Vegas/mysterious mohave co. az, Big Pine Key Fla.
    Shooter
    ULarge Format
    Posts
    2,713
    Images
    20
    Cool....the good news just keeps coming...

  3. #3
    Lachlan Young's Avatar
    Join Date
    Dec 2005
    Location
    Blairgowrie, Scotland; York, England
    Shooter
    Multi Format
    Posts
    576
    Images
    3
    When do the Gevalux trials start...? (velvet surface warmtone paper mmm...)

    Also, how easy is it to make handcoated FB glossy paper?

    Many thanks,

    Lachlan
    "A squid eating dough in a polyethylene bag is fast and bulbous...got me?" Captain Beefheart

  4. #4
    David A. Goldfarb's Avatar
    Join Date
    Sep 2002
    Location
    Honolulu, Hawai'i
    Shooter
    Large Format
    Posts
    17,173
    Images
    20
    1/8" of bead on each side is pretty good. Using the float method with albumen, I usually coat 11x14" for an 8x10", but I think the minimum would be 9x12".
    flickr--http://www.flickr.com/photos/davidagoldfarb/
    Photography (not as up to date as the flickr site)--http://www.davidagoldfarb.com/photo
    Academic (Slavic and Comparative Literature)--http://www.davidagoldfarb.com

  5. #5
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,938
    Images
    65
    Quote Originally Posted by Lachlan Young
    When do the Gevalux trials start...? (velvet surface warmtone paper mmm...)

    Also, how easy is it to make handcoated FB glossy paper?

    Many thanks,

    Lachlan
    Lachlan, the velvet warmtone is possible. The Strathmore Velour is similar to a velvet surface without baryta and imparts a warm tone. Using a warm toned emulsion (I have made one) and/or a warmtone developer, you can get quite nice results.

    Coating on FB Baryta glossy paper will yield a glossy print. The yield is lower than other papers due to apparent defects in the paper and defects due to the nature of the baryta itself. It is a more expensive paper, but gives good quality prints.

    PE

  6. #6
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,938
    Images
    65
    Quote Originally Posted by David A. Goldfarb
    1/8" of bead on each side is pretty good. Using the float method with albumen, I usually coat 11x14" for an 8x10", but I think the minimum would be 9x12".
    For an 8x10, I use a 9.5" x 12" sheet and 12 ml of emulsion.

    PE

  7. #7

    Join Date
    Aug 2006
    Shooter
    35mm RF
    Posts
    218
    Photo Engineer, I read in one of your posts that you have hand coated an Azo equivalent. While I am not yet in a position to do contact printing (just 35mm equipment for now), I am a bit intrigued/curious about your approach to doing such.

  8. #8
    David A. Goldfarb's Avatar
    Join Date
    Sep 2002
    Location
    Honolulu, Hawai'i
    Shooter
    Large Format
    Posts
    17,173
    Images
    20
    Keep an eye out for PE's next workshop. I sat in on his New York workshop just for one day, and I was very impressed by the things they were working on. Obviously the participants were all beginners in silver gelatin emulsion making, but they were able to make an Azo-type emulsion in three contrast grades without much difficulty, and they learned about tweaking the formula to do things like adjusting the toe, and could coat on a variety of papers, providing much more control over the process than one can get with Azo or a similar type paper. Of course it's also a lot more work to coat your own and requires some practice to produce consistent coatings, but if you want that level of control, it may be worth it to you.

    Participants also worked on coating film and plates with an ortho emulsion of around EI 40, and it was good to see that you could make a usable film with modest materials and equipment.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
    Photography (not as up to date as the flickr site)--http://www.davidagoldfarb.com/photo
    Academic (Slavic and Comparative Literature)--http://www.davidagoldfarb.com

  9. #9

    Join Date
    May 2004
    Shooter
    8x10 Format
    Posts
    236
    David, thanks for the info. I hope to be able to participate in of the workshops. One part of me just wants a perfect factory made paper to print all day and any day. Another part of me wants to see how different surfaces would look. I am wanting to see B&W matte prints with a velvety surface. Something similar to platinum/palladium but with the added detail of an emulsion on top of the paper.

  10. #10
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,938
    Images
    65
    Quote Originally Posted by David A. Goldfarb View Post
    Keep an eye out for PE's next workshop. I sat in on his New York workshop just for one day, and I was very impressed by the things they were working on. Obviously the participants were all beginners in silver gelatin emulsion making, but they were able to make an Azo-type emulsion in three contrast grades without much difficulty, and they learned about tweaking the formula to do things like adjusting the toe, and could coat on a variety of papers, providing much more control over the process than one can get with Azo or a similar type paper. Of course it's also a lot more work to coat your own and requires some practice to produce consistent coatings, but if you want that level of control, it may be worth it to you.

    Participants also worked on coating film and plates with an ortho emulsion of around EI 40, and it was good to see that you could make a usable film with modest materials and equipment.
    David, thanks for your kind remarks. It was a pleasure to finally meet you in person. We all enjoyed your visit, and the time we spent with you.

    The class had a very good week, with things going very well for all of us.

    Thanks for coming by.

    PE



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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