More on coating and coating blades

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by Photo Engineer, May 11, 2007.

  1. Photo Engineer

    Photo Engineer Subscriber

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    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. dwross

    dwross Subscriber

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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. Photo Engineer

    Photo Engineer Subscriber

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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. ben-s

    ben-s Member

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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.
     
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  5. Alex Hawley

    Alex Hawley Member

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    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?

    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.
     
  6. ben-s

    ben-s Member

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    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?
     
  7. dwross

    dwross Subscriber

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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. Alex Hawley

    Alex Hawley Member

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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/

    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.
     
  9. dwross

    dwross Subscriber

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    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
     
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  10. dwross

    dwross Subscriber

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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.
     
  11. Ole

    Ole Moderator Staff Member Moderator

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    just make sure you keep all the "[" and "]" intact...
     
  12. Photo Engineer

    Photo Engineer Subscriber

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    It must be something in the air Denise, I get the Formulary baryta and coat on it 'as cut' and it does not cause me any problems. Alex reviewed paper coated that way with no serious problems.

    I will agree though that the chance of defects goes up whe using baryta paper due to the blade sticking to the baryta as it swells and making movement of even the smooth blade difficult.

    As for papers, I've found that for strength to survive both the coating and processing steps, you would need a hot press paper of 90# or higher. With cold press papers you would have to start at about 120# or 150#. I've used a textured paper of 300# that makes excellent prints for postcard use.

    PE
     
  13. dwross

    dwross Subscriber

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    Ron:

    The swelling and sticking is the grain issue. Fortunately, contact printing flattens out any bumps. Blade-coating baryta with the grain (so that the paper cups up in one straight curl top to bottom rather than washboarding) is the easiest and most successful paper I've found. I don't care much for the look of baryta, a fact I've regretted more than once given its ease of use. Try coating the other direction and see what you think (I cut an 11x14 sheet in half across the width for the 4x5 blade).

    d
     
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  15. dwross

    dwross Subscriber

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    Ron:

    Something just occurred to me. There is no reason to assume that the Formulary is consistent on their paper cutting. If they are trying to minimize wasted paper, especially for special orders, the grain could vary from sheet to sheet. I'll ask them tomorrow and report back to you.

    d
     
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  16. ben-s

    ben-s Member

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    I managed to coat 4 sheets this morning before I ran out of emulsion.
    These are coated with my basic blade, charged with approximately 8ml of emulsion, onto cheap watercolour paper.
    The paper was soaked in lukewarm water for about a minute, and then squeegeed onto a plastic support plate, as per Denise's method.
    After coating, I allowed the emulsion to gel for a few seconds, and peeled the paper from the coating support. The paper was then placed onto a large sheet of perspex to dry.
    The drying stage was very dodgy, in that I have no way of leaving the darkroom (the loft) without flooding the place with light.
    I had to dry the prints with a hairdryer in order to box them up so I could leave the darkroom.

    I'll post a proper scan of the latest prints when they are dry.
    For now, though, I've attached a couple of photos of the results. the red and green rings indicate and identify defects in the coating as follows: red=handling defects (clumsy damage :tongue: ), green=coating defects.

    I think the handling defects could be avoided by setting up a proper drying system, and also adding a hardener to the emulsion before coating.

    These are the best coatings I've made so far. Unfortunately I underexposed the panoramic one quite badly.
    Typically, I also printed it on the edge of the coating as well, so there's a triangular chunk of image missing.

    I'm going to try and reprint it on one of the other sheets I coated.

    Lessons from today:
    1: Find out how much emulsion you have left before beginning a coating session :D
    2: I need a better drying system. IE. One that is lightproof. I need to be able to leave the darkroom before the coatings are dry.
    3: Coating is not that difficult, even with primative gear.
    4: Wetting the paper prior to coating helps the process a great deal. Squeegeeing it onto a plastic support helps even more
    5: I need more than 8ml in the blade
    6: I really do need to level the bench up.
    7: I think I need to add hardener to the emulsion before coating.

    In conclusion then, Most of my problems would evaporate with slightly improved equipment, and small adjustments to chemistry and technique.
     

    Attached Files:

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  17. Photo Engineer

    Photo Engineer Subscriber

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    Ben;

    Best wishes in your efforts.

    To all who coat on wet paper, be careful. I have had it stick to the drying surface, and have found that it may be better to air dry hanging after a short time gelling on the flat surface.

    PE
     
  18. Alex Hawley

    Alex Hawley Member

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    That's true. After trimming the sheets to 8x10, I could see no indication of which direction the coating blade was moved, nor can I discern any paper grain effects. I'm talking about the baryta base.

    Visually comparing the hand coated baryta prints to prints on manufactured paper, I cannot see any significant difference in the surface textures. The hand coated stuff looks like any other glossy fiber base paper.
     
  19. Photo Engineer

    Photo Engineer Subscriber

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    Thanks, Alex.

    PE
     
  20. dwross

    dwross Subscriber

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    Ben-s:

    Yahoo! Sounds like it's coming along. Thanks for the report. As more of us start doing this, the knowledge base should start building up.

    To make a light trap out of a not-so-dark room (the times I've worked in 'spare' bathrooms, I've gotten as primitive as hanging a towel rod over the top of the door to drape a blanket. That allows a quick enough escape for anything but film.

    re: baryta paper (at least the variety sold by PF). The baryta coating covers one surface of the paper. The barytes (barium sulfate) is added to the gelatin to make the paper smoother, to increase the whiteness of the base color, and to increase the coverage of the emulsion. I don't know what the backing paper is, but it looks like a thin bristol board type. The grain isn't visible. It certainly isn't a screen-dried watercolor paper where the back side is easily identifiable by the visible screen marks. After a successful blade coating, there is no indication of which direction the blade was pulled over the paper. During blade coating, the odds of success are greatly improved by watching the grain. And with PP coating, watching the grain is vital (at least in my experience).

    If you happen to have a couple of pieces of uncoated baryta laying around and are willing to sacrifice them to science, try this:

    Tear one so that you get two pieces with the long dimension of the original piece going the long dimension and the other one so that the short dimension of the original becomes the long dimension. Set them on a dry, smooth surface and spritz with water (I used the spray bottle I have for ironing). Stand back and watch the show. The paper will cup up in a smooth line on one and washboard on the other.

    As I said yesterday, it occurs to me that the paper may not be consistent from pack to pack. I had an unopened pack here that I just opened and ran the test on. The results were the same as my previous observations, but that's still not enough evidence to say for sure and all time.

    Which brings me to a micro-gripe: There is too much 'conventional wisdom' forming and setting rock-hard based on far too little (primarily) anecdotal information. If one person with some credentials and virtual gravitas makes a pronouncement, it is expected that is the end of that. A "Trail Closed" sign is set at the beginning of the path.

    People sharing their experiences and observations is a mixed blessing. I'm certainly happy to let someone else make a few of the expensive mistakes. I love learning from other folks. An the other hand - and this is a biggy - if those experiences, trials, and observations are technically flawed or simply colored by a hidden paradigm that you may not support (bigger is better, glossy is better, glossy is tacky, if it was good enough for Kodak, it's good enough for me, etc, etc, etc,) and you don't take the risk of walking around that "Trail Closed" sign, you stand the chance of missing out on a lot of fun and satisfaction.


    Sincerely,
    d
     
  21. Photo Engineer

    Photo Engineer Subscriber

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    Denise;

    I agree. Trial and error and personal (even anecdotal) experiences are often preferred over Ex Cathedra pronouncements by an expert. That is why I'm so happy here that others are chiming in.

    I have had bad experiences with light weight blades, and so have been particularly pleased seeing Ben's results.

    As for the differences in grain in baryta paper, I will have to go back and check out some sheets, but so far I don't see it. I do see it on some other textured cold press papers though. You can see differences depending on the direction of the texture.

    BTW. Baryta is a hot press paper which is pressed at least twice. It is hot pressed during the making and then is again pressed after the baryta is applied in order to compact the baryta to get the desired surface. The pressure (among other things) determines the level of gloss.

    I have some sheets of a matte baryta and a super rough baryta here that you might want to try. Each is totally different from the smooth that we have from the PF. In total, there are 3 or 4 surfaces available in baryta, each with different characteristics. It is also possible to get RC in several sources and SW FB. I don't recommend either of these, but then I hate Ex Cathedra comments ( :D ) and so mention it in case anyone would like a sheet or two to try.

    PE
     
  22. dwross

    dwross Subscriber

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    Ron:

    I'm delighted that you have a sample of matte commercial baryta. I'd love to look at it. Could you hang on to it for awhile? I've got paper samples piled so high and deep here that it would just get lost, and also I know you're busy packing up for Montana.

    I'm going to try my hand at making baryta paper. I know that the glossy is beyond me. Apparently, it takes many passes through a calendering machine to produce a high gloss, but I should be able to manage a matte-type. (Now, that statement may just be the ultimate in hubris.) I finally got the barium sulfate. "Barytes" used to be available through Daniel Smith Art Supplies, along with things like China Clay for printmaking. For some reason, it's gotten hard to get. I found it from a chemical supply house in Florida. It took my business license and a statement of intent, but after that it didn't even ship HazMat. Go figure. I'll keep you informed. Hopefully, the Great Baryta Grail will go better than my Flubber Adventure!

    d
     
  23. Photo Engineer

    Photo Engineer Subscriber

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    Denise;

    You can use 60% medical barium sulfate paste for this operation. (pun intended) If you don't have pre-prepared paste, you may need to use a ball mill to get the material down to the right particle size for coating.

    Mixing it with gelatin to get the right thickness, adding surfactant and hardener and coating will give you a matte 'rough' finish baryta which looks very interesting. It should be fun.

    You may need to coat this with a blade at 10 mil instead of 5 or 7. In fact, you may need to go to 20 mil for proper coverage. It depends on the viscosity and coverage of the material.

    PE
     
  24. dwross

    dwross Subscriber

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    Hi All:

    I have just posted the current update of my emulsion research. The material relating specifically to puddle pushers is here:

    http://dwrphotos.com/blog/Section7/Papers.htm

    Hope it helps. Happy Emulsion Making.
    Denise
     
  25. Alex Hawley

    Alex Hawley Member

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    Fascinating Denise, and a most well-done presentation. Thank you for making this info available.
     
  26. Emulsion

    Emulsion Member

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    Denise,

    I agree with Alex, great presentation and content.

    I concur with the sentiments of the "I love Emulsion" page. I'm sure this forum will enable a whole new batch of amateur emulsion making to occur. I look forward to your Jan 2008 update.

    Thanks for sharing all this wonderful information!