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The cracking might be due to insufficient clearing of the dichomates. 1) they are usually (if not always) single transfer prints, so the dirchromate gets trapped between the gelatin and the final support and 2) the thicker print makes it more difficult to get the dichromate out.
It appears (but as far as I know not proven) that any dichromate left in the image will slowly cause the gelatin to harden further over time making the gelatin more brittle. Might not be an issue if the print is kept flat...if bent, the gelatin might crack.
But even thinner prints w/o relief might have these same problems if not cleared sufficiently. But double transfer prints generally need little or no clearing (other than a good wash) as the dichromate is easily removed by the double transfer itself.
Please note that I do not write this as an absolute authority on the subject -- but offer this as the consensus of opinion of some carbon printers on the carbon forum, based on research, etc.
Vaughn
Last edited by Vaughn; 07-22-2011 at 08:36 PM.
At least with LF landscape, a bad day of photography can be a good day of exercise.
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Seems to make sense. Perhaps it is another creative variable that can be used, high relief, low relief, tint, support paper, etc.
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The difference between a coating rod and a coating blade is waste. If you are coating carbon, this is not an issue, but when coating silver, Pt or Pd, it can become an issue. There is generally more waste with a rod.
PE
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 Originally Posted by gmikol
That's not so much wire as rod stock. Good luck winding that around anything...
Yes; that was more a demonstration of the formula than anything.
The plastic or stainless steel threaded rods sound good. And not that it would be too hard to figure it out empirically, but I wonder what the relationship is between thread size and coating thickness?
Shoot... you could probably even use expansion springs. http://www.mcmaster.com/#extension-springs/=dbx0gj
From the film shooters will rise a well developed practice of the alternative processes that, in time, will be adopted in the age of the digital image to free it from the extreme boringness of pressing print.
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Originally Posted by holmburgers
Yes; that was more a demonstration of the formula than anything.
The plastic or stainless steel threaded rods sound good. And not that it would be too hard to figure it out empirically, but I wonder what the relationship is between thread size and coating thickness?
Shoot... you could probably even use expansion springs. http://www.mcmaster.com/#extension-springs/=dbx0gj
Ballpark: coating = 1/10 wire diameter (round wire, packed). There are variants on the basic meyer rod: gaps between windings, double wound, machined (instead of actual wire). In the case of threaded rod, not just the depth of thread, but the shape of the 'valleys' need to be taken into consideration.
I actually tried using a expansion spring (the kind used for a garden gate) - it worked surprisingly well. Am I still using it? No 
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Oct workshop
Originally Posted by Photo Engineer
That company is about 5 - 10 miles NE of George Eastman House. Mark has a few of them here IIRC, so those coming to the workshop in Oct. can try one out I guess.
PE
Yes, I'd like to try that on a 12x15 inch glass plate. I suppose the plate would need to be surrounded by glass edge pieces of the same thickness and all pre heated.
Michael
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Michael:
My method does not require dams in the sense that some other methods do. I can use one large blade and shim it down to any width. A blade can coat any length provided you have arms long enough!  Due to the huge heat capacity of the steel blades, a heated plate is not necessary. It can be at room temperature, but heating can help a bit. I usually blow on the plate before coating. Mark Osterman does the same.
PE
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Dust has been found in my emulsions, I have a bulb to use that will be put into play next time. Thanks for the heads up.
Pouring over the edges helps to prevent frilling or edge separation. It also reduces the size of a "picture frame" effect. That is a thinner border that forms when drying. A coating blade would need a pretty large well to coat a large piece of glass, but then, it does put emulsion on thinly.
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I use a gold mesh coffee filter to remove most dust and dirt. It works very well.
As for frilling, I file a slight bevel on the edges of my plates to remove sharp edges and to give the edge a "tooth". Mark Osterman's influence again! The blade method gives an even coat except at the edges. The start and finish of a pass can introduce defects and that is where a "dam" is useful. You coat longer than you want and the dam is the part with start and stop defects. I use 12 ml of emulsion to coat 1 foot square at 5 mil undercut. I use about 15 ml at 7 mil. I usually coat plates at 7 mil.
An afterthought:
You can use a full width rod with cardboard or metal (SS) edge guides to act as dams. This will prevent the spread of the emulsion common to the use of these rods. If you use glass edge pieces, then they should be thicker than the plate you are coating, and of course the rod should be full width for the plate. I think that using the edge as a dam with most methods is as good or better than using shims, but they both work.
PE
Last edited by Photo Engineer; 07-26-2011 at 02:24 PM.
Reason: Afterthought
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Just a quick update to this thread...
I started thinking again about Meyer rods and went back and looked at RD Specialties.
They have a section for Standard Lab Rods and I emailed them for a price quote.
These rods will coat up to 12" wide and not one of their options (including formed rods) costs much more than.... drumroll please ... $30! Depending on your specifications, you're looking at probably $25, plus shipping.
For thicker carbon tissues you might have to get a "gapped" wound rod, but I can't say for sure.
Worth looking into if you're interested.
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