Coating rods

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by GLSmyth, Apr 7, 2014.

  1. GLSmyth

    GLSmyth Member

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    I am collecting materials to give making AZO a try and one of the last things on my list of things to get is a coating rod. I found some at http://www.gardco.com/pages/application/ap/wirewound_rods.cfm (most other places force one to request a quote, so I assume that they are looking to sell in bulk). The thing is that I am not sure which one would work best. Does anyone have a recommendation or a better source?

    Cheers -

    george
     
  2. jeffreyg

    jeffreyg Subscriber

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    George,
    If they are the same coating rod as for pt/pd check with Bostick and Sullivan in Santa Fe, NM. I have gotten glass rods from them and they come in different sizes.

    http://www.jeffreyglasser.com/
     
  3. dwross

    dwross Subscriber

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  4. GLSmyth

    GLSmyth Member

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    I initially posted that a puddle pusher would not work but have edited this post because it may. 35mm film is about 5mil in thickness and that is the clearance I need, so I may be able to place a strip on either side and place the puddle pusher over it, giving a 5mil clearance over the paper. A coating rod would be much easier (I have used one and it makes coating a cinch), but if I cannot figure out which size to get then I will be spinning my wheels.

    Watching at the video it looks like the poster has something on either end of the puddle pusher - attaching 35mm film should allow for the required clearance.

    Cheers -

    george
     
    Last edited by a moderator: Apr 7, 2014
  5. Prof_Pixel

    Prof_Pixel Member

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    George,

    Didn't Ron (PE) have a recommendation?

    Fred
     
  6. dwross

    dwross Subscriber

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    I think I'll amend "suggest" to "beg":smile:. Please take a look here:

    http://www.thelightfarm.com/Map/PaperAndCoating/PaperAndCoatingPart3.htm

    You are correct, of course. An unaltered puddle pusher only pushes the emulsion around. You need a gap between the paper and the coater. Wrapping tape around a glass rod creates a coating gap.

    There are a number of reasons this works better than a wire-wrapped metal bar. Silver emulsion will eventually corrode even stainless steel. Glass is corrosion-proof. It's dimensionally stable. Puddle pushers are cheaper. They are far more adaptable to experimentation and different emulsions because you easily set a custom gap height with tape.

    I don't even know how many acres of paper and film I have successfully coated, but it's a lot. I'm into my third pound of silver nitrate. I'm giving you good advice.
     
  7. Lee Rust

    Lee Rust Subscriber

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    George,

    Nick informed me that the wirewound coating rod we used in the AZO workshop last month is the RDS #130 'gapped' rod. Theoretical coating thickness is 11.7mils, well outside of the 5 to 7mil range that was recommended by Ron. I asked Ron about this and he guessed that the #130 rod was chosen mostly because it was available and for no other particular reason. RDS has many other rods available. Their #56 rod is listed at 5.04 mil coating thickness and the #80 rod at 7.20 mil.

    Here's a link to the RDS download page for specifications: http://www.rdspecialties.com/techinfo.html

    Of course, a glass rod wrapped in tape might work just as well and cost a lot less.

    Regards,

    Lee Rust
     
  8. dwross

    dwross Subscriber

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    Is it possible there was a glitch in the communication? Coating thickness is considerably greater than final, dried-down thickness. 11-12 mil will dry down to 5 to 7 (generally, a good final thickness). I aim for a 10-12 mil gap. My guess is that's the reason the class went with the #130.
     
  9. Lee Rust

    Lee Rust Subscriber

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    Denise, the #130 wire wound rod with 11 mil gap worked fine and Ron's custom built edge coater with 5 mil gap also worked very well. Prints made from the thicker emulsion made with the rod did seem to have more contrast.
     
  10. dwross

    dwross Subscriber

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    Hi Lee,
    That's the lovely thing about handcrafted. Each hand crafts as each heart desires. I favor the appearance that comes from a thicker coating of emulsion, but you make a really excellent point. There's a lot of wiggle room for technique and a lot of ways to get from Here to There.

    I hope you and George and the others in the class post here soon and often. You could revitalize the joint!
    d
     
    Last edited by a moderator: Apr 7, 2014
  11. Photo Engineer

    Photo Engineer Subscriber

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    I suggest a 5 mil to 7 mil gap for paper and a 7 mil to 10 mil gap for film. The one we used at class gave us about 11 mil and the pictures were just fine. Right?

    Nick can give you a source and product #.

    PE
     
  12. DREW WILEY

    DREW WILEY Member

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    The carbon printing forum, hosted by Sandy King, sometimes does group orders for precision stainless coating rods.
     
  13. dwross

    dwross Subscriber

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    Absolutely. Just as long as folks understand that coating paper does not require expensive, specialized lab equipment, and that there is a lot of tolerance in the specs, I'm content to stop nagging. (For now :smile:.)
     
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  15. Athiril

    Athiril Subscriber

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  16. Vaughn

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    Being highly imprecise, I used a pipe with electrical tape wound around each end (same number of turns each side!) for pouring my first carbon tissues. One can afford a bit of sloppiness when one does not add expensive metals into the gelatin! Warming up the pipe (it was plastic) and resisting the temptation to roll the pipe as one draws it across helped. Good luck...and do check out LightFarm!
     
  17. dwross

    dwross Subscriber

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    Hi Athiril,
    Thanks for looking up the numbers on tape! Scotch Magic is a easy candidate for taping puddle pushers. For some reason I've totally forgotten, I had a couple of rolls of 850 when I started playing with emulsions and I settled into it as my tape of choice.

    One note: 0.9 mil of the 850 is the adhesive. That's one reason I like the stuff so much. I just count each wrap as 1 mil because I assume the adhesive mashes down to nearly nothing. I also have to assume the adhesive on Magic Tape is also about 0.9 mils. But, as said, "stressing the mils" isn't necessary. Vaughn's approach to carbon could be the role model for our work. He's a master of his craft, without resorting to expensive accessories.
     
  18. Vaughn

    Vaughn Subscriber

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    Actually, I push the gelatin around with my fingers now...:D
     
  19. GLSmyth

    GLSmyth Member

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    Thanks for all of the excellent information. I have to send back the magnetic heating plate I got so it will be a little while longer before I can get going. My thought is that there are a number of areas where being absolutely precise will not have as much effect as other areas (as is always the case) so I will start with creating a gap with the rod.

    Amusing that Vaughn mentioned pushing the gelatin around with his fingers as that is exactly what I did with one of my prints in the workshop. The print actually came out pretty good with one exception - there was an area that was so thick that the fixer was not able to get through, so there's a finger of brown across the top.

    Cheers -

    george
     
  20. GLSmyth

    GLSmyth Member

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    PE -

    Yes, just fine - actually, better than fine.

    Out of curiosity, why thicker for film? I would think that it would be the other way around because the emulsion would sink a bit into the paper, but not so with the film.

    Cheers -

    george
     
  21. Vaughn

    Vaughn Subscriber

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    George, my guess is that a film emulsion has to block about twice as much light as does a paper emulsion. A film negative has to block light in only one pass...the silver has to be packed in pretty dense to block light. Film emulsions do the heavy lifting. The silver in a paper emulsion gets to block the light twice -- once thru the emulsion, then again as the light is reflected off the paper base and towards our eyes. That's Vaughn's totally unscientific explanation of the day...LOL!
     
  22. Photo Engineer

    Photo Engineer Subscriber

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    Film Needs about 300 mg / ft sq of silver, but paper needs 1/2 or less of that. This is the reason. You need dmax with film.

    PE
     
  23. GLSmyth

    GLSmyth Member

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    Thanks, that makes sense.

    Cheers -

    george
     
  24. Photo Engineer

    Photo Engineer Subscriber

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    One additional thought though. Mark, Nick and I spent a day trying to coat plates with rods and found an unusual ripple effect on our plates. They are working on this and I have to go over again in a few days to continue this work with them. We hope to get a handle on it.

    PE
     
  25. Andrew O'Neill

    Andrew O'Neill Subscriber

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    Resorting to a cheap accessory, I use a comb from the dollar store. :smile:
     
  26. Photo Engineer

    Photo Engineer Subscriber

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    This is excellent for the artsy look. We have done many things in our workshops at GEH.

    However, nothing beats a blade or a rod for sheer quality. You can approach current production quality this way.

    PE