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  1. #1
    Photo Engineer's Avatar
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    More on coating and coating blades

    First, let me describe the art of coating a bit.

    Those of you that coat anything at all light sensitive know by now that the amount of coated material governs the speed, contrast and dmax. The more you coat, the higher each of these variables go. Of course, speed is more limited in the change and the other two can vary more.

    That said, now I can go directly to describing the application of anything by brush. You will see brush strokes in the finished print that are the result of high and low quantities of material being applied. With enough material, you eventually get an even coating and (hopefully) the right contrast and dmax.

    With a puddle pusher or a wire wound rod, you must pour on the liquid light sensitive material ahead of the rod. The instant it is poured onto paper support, it begins to absorb into the paper. As you move the rod, you get leakage out the edges and the paper begins to swell. The faster or slower you move, the more you put down on the surface and a varying quantity of the material is absorbed into the paper and coated on the surface. This creates the possibility of light and dark patches in the coating.

    Spraying on the light sensitive medium is just fine, but like any painting technique, you must avoid light and dark spots and runs.

    The above three methods are an art that one acquires with time, but it can produce excellent materials.

    Now we come to the coating blades....

    The paper blades have a leading edge that holds the paper flat as you move over the surface, and a 'well' that contains the light sensitive liquid so you place in the blade just the amount you want to use. It does not leak out of the edges. Surface tension holds it in the narrow gap at the coating (trailing) edge.

    When you pour in the light sensitive liquid, the blade confines the liquid to the 1/2" well and therefore prevents swell elsewhere. As you move the blade, the gap allows a precise amount to escape from the trailing edge of the blade. This gap can be varied from about 0.002" to 0.010 under normal operation, but I have gone higher than that. The larger the gap, generally the more viscous the light sensitive liquid must be and/or the cooler the operating temperature.

    Typically, an 8x10 sheet will require an 11x14 sheet of paper. There will be 1 - 2 inches of 'bad' coating at the top, and up to 1" of 'bad' coating at the bottom with tracks of bad coating about 1/8" wide down the edges. The blades are wider than the coating area for just this reason.

    This too is an art to some extent, but IMHO, it is an easier one to match and one that ultimately yields better coatings than any other method and with greater economy of time and chemicals.

    All of these methods can be used by anyone for excellent hand coated prints, but the blade, in a slightly different form, was actually used in production by several companies about 70+ years ago to produce film and paper for sale. They are still used today at Kodak to make small sample coatings of new emulsions or when it is necessary to use tiny amounts of chemicals due to cost or availability.

    I hope this answers the bulk of the quesitons I have gotten.

    BTW, for those that complain that I'm 'advertizing them', I make no profit, and the price to me continues to go up as the reject rate increases. If I cannot solve the production problems, I will publish the plans when I reach the point that I've paid for what I have made so far, and then I will step out of this business and turn it over to someone else. That is my disclaimer. I'm doing this as a 'public service' if you will.

    Well, actually even if I do solve the production problems, I'm thinking of getting out of this business and handing it over to someone else.

    PE

  2. #2
    dwross's Avatar
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    Not quite the whole story. Puddle pushers work fine with a little paper prep. I've been working the problem off and on for a couple of months now. As per my standard research m.o., I've started off scattergun to get the big picture, taking copious notes as I go along and start to focus in on the most likely path.

    Working with a 9 in. "Puddle Pusher" glass coating rod and a dozen kinds of papers, here's what I know today:

    1) Paper prep: Starting with an 11 x 15 sheet cut along the longitudinal axis (i.e. four pieces from a 22x30 in. sheet of paper) fold up both long edges an inch wide, forming a 9 inch-wide constrained path for the PP and emulsion. This eliminates emulsion seepage around the edges of the glass rod. Place strong clear tape (I use 3M storage tape) on the inside edge and fold it over the top to the back side. This creates a water resistant, smooth surface that allows the PP amd emulsion to be pulled smoothly and evenly along the surface.

    2) Most papers coat best when first soaked a minute or two in very warm water and then squeegeed off on a large sheet of thick plexiglass (Surface tension holds the paper flat and largely eliminates the swelling problem.) I compensate for the water left in the paper by increasing the percent gelatin. (Note: variable alert.)

    3) Wrap the ends of the PP in several layers of 3M polyester film tape #850. This holds the body of the PP off the paper at a constant height. (Note: variable alert - different papers require different gap sizes.)

    Summary as of May 12:
    1) Prep dry paper and stack in darkroom. Have plexi sheets ready (mine are 14 x 20 x 3/8 inches) Have water soak-bath ready (large Pyrex lasagne pan on hot plate) and of course, PP and emulsion.
    2) Soak paper, drain a second, lay on plexi, squeegee, lay PP at top edge of paper, spoon (about 1T) emulsion in front of PP, and slowly and evenly pull the emulsion down the length of the paper. Mark the borders of the coating (easily visible when the emulsion is wet). Set aside paper and plexi, undisturbed. Take new sheet of plexi for next sheet of paper. At the end of the session, the emulsion has set enough to hang the sheets to dry.

    It's not perfected yet, but even now, it's a matter of material wastage, not failure of the technique. By the first of June I hope to have step-by-step illustrated instructions on my website.
    **************

    I feel like a broken record sometimes, but this is doable, folks. I'm not particularly happy that the dialogues on this forum continually turn to factory production and quantum level chemical engineering. I can't imagine what purpose is served by selling the myth that silver gelatin emulsion making is beyond the grasp of mere mortals. Yes, it takes a bit of dedication, but no more than a gourmet culinary pursuit and there are whole TV channels dedicated to those. Forget the film and paper factories. Let's create the Emulsion Channel!

    d

  3. #3
    Photo Engineer's Avatar
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    I was hoping that Denise would respond with her unique methodology.

    It works using what she describes and is a major step forward.

    I endorse what she says....

    PE

  4. #4
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    Very interesting info. Thanks.

    I've managed to build a basic coating blade from Ron's descriptions and had moderate success coating commercial liquid emulsion with it. It needs more work, but I think I've found solutions to most of the major problems I've had.

    I'll second what Denise said about the paper coating better when it has been briefly soaked in warm water.

    I've tried anodised aluminum plate and melamine faced plywood as backing materials, and both work. I prefer the ply, as it seems to gel the emulsion off quickly, but not too quickly. There is plenty of time to fill the well of the blade before the emulsion begins to gel, but the thin coated layer gels in a few seconds.

    I've coated on watercolour paper and also laser printable OHP film with reasonable success. I haven't tried inkjet OHP film yet.
    Last edited by ben-s; 05-12-2007 at 08:28 PM. Click to view previous post history. Reason: missed a word
    Lens caps and cable releases can become invisible at will. :D

  5. #5
    Alex Hawley's Avatar
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    Quote Originally Posted by dwross View Post
    Puddle pushers work fine with a little paper prep.
    Denise, what type of paper base are you working with? I can see the puddle pusher working good for strathmore or a watercolor-type paper base, but what about baryta?

    Forget the film and paper factories. Let's create the Emulsion Channel!
    What we need to do is persuade PBS or some other sorta niche-type broadcaster to do an Analog Photography show. Heck, there's gotta be as many or more of us than their are Registered Black Angus owners.
    Semper Fi & God Bless America
    My Photography Blog

  6. #6
    ben-s's Avatar
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    Quote Originally Posted by Alex Hawley View Post
    ...
    What we need to do is persuade PBS or some other sorta niche-type broadcaster to do an Analog Photography show. Heck, there's gotta be as many or more of us than their are Registered Black Angus owners.
    How about taking matters into our own hands?
    Decent camera work and editing fed out via youtube or similar?
    Unfortunately, I'm rather the wrong side of the pond to do the production side of things, but there must be someone in the right part of the US who is interested in emulsion making and knows how to produce a video?
    Lens caps and cable releases can become invisible at will. :D

  7. #7
    dwross's Avatar
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    Ben-s:

    It's very encouraging to hear that you're experimenting and getting good results. I'd like to hear more. I use warmed granite tiles. They work well, but the plywood sounds smart. The granite can get a little heavy by the end of a printing session.

    Alex: I have a fondness for hot press (smoothish) watercolor papers. Not too slick (baryta) or too rough (Strathmore). Right now, the most encouraging papers are Fabriano Artistico HP, Somerset Satin, and Arches HP, and maybe Rives BFK. Having said that, I think baryta is going to be a winner in the PP race - with one important caveat: The paper (at least what I've been buying from the Photographers' Formulary) is very strongly grained. The paper cups/curls on the longitudinal axis, and it doesn't take 'no' for an answer. The Formulary cuts their baryta opposite what I would. When I'm working with a blade, I cut 11x14 inch sheets cross-wise so that I get two 11x7inch sheets - perfect for the 4x5 blade. With the 9 inch PP I need more paper. The 11x14 size would be ideal, but the grain runs the wrong direction. When I constrain the long edges with tape, it doesn't allow the paper to swell along that axis, and it washboards like you wouldn't believe. You can't squeegee it down. So...on my ToDo list is to order a package of baryta paper large enough to cut down to size with the longitudinal axis on the long dimension (i.e. across the width). I'll keep you informed, but I have no doubt it will work beautifully.

    d

  8. #8
    Alex Hawley's Avatar
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    Thanks Denise. As you know, I'm keeping an eye on all this but haven't taken the plunge yet. Seems I keep edging closer though/

    Quote Originally Posted by ben-s View Post
    How about taking matters into our own hands?
    Decent camera work and editing fed out via youtube or similar?
    Unfortunately, I'm rather the wrong side of the pond to do the production side of things, but there must be someone in the right part of the US who is interested in emulsion making and knows how to produce a video?
    PE had a short video on one of those sites, I forget which one. And I'm sure not the one to produce anything nor decide on the media used., But, just floating the idea, (and maybe it should be another thread), a niche TV series as Denise suggests, may get more people into the analog side of this art and stimulate and increased interest from the manufacturers.
    Semper Fi & God Bless America
    My Photography Blog

  9. #9
    dwross's Avatar
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    Quote Originally Posted by Alex Hawley View Post
    PE had a short video on one of those sites, I forget which one. And I'm sure not the one to produce anything nor decide on the media used., But, just floating the idea, (and maybe it should be another thread), a niche TV series as Denise suggests, may get more people into the analog side of this art and stimulate and increased interest from the manufacturers.
    The site is Photographers' Formulary. Tony Mournian did the video and he's done others. He's great.
    http://www.youtube.com/watch?v=i4q0Ryh9pBE
    Last edited by Ole; 05-13-2007 at 08:38 AM. Click to view previous post history. Reason: Fixed quote

  10. #10
    dwross's Avatar
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    I'll have to figure someday how to get the quotes to come out right. The above quote is from Alex Hawley.

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