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Photo Engineer
06-28-2013, 07:35 PM
Two methods are used. One is to use an undercut roller and have 1" of uncoated film on each edge. It is called selvedge. The other method used is air bearings. The paper runs on a curtain of air, suspended on a cushion of air. With this latter method, the film can turn corners of 45 to 90 degrees.

PE

Prof_Pixel
06-28-2013, 08:45 PM
Historically, festoon loop dryers and spiral dryers have been used in the photo industry. I know DuPont used such dryers.

AgX
06-28-2013, 09:17 PM
Foma for example still have a festoon dryer.

Photo Engineer
06-28-2013, 11:07 PM
And, EFKE used festoon drying until they closed the plant.

PE

Michael R 1974
06-29-2013, 03:12 PM
I have two coating questions (after reading Bob Shanebrook's book). 1) Why would one ever prefer a shiny overcoat vs matte? It is a really annoying characteristic of TMax films for example. 2) With a tabular grain emulsion, how do they get the flat grains oriented after the emulsion curtain pours onto the base? In a cross section of TMax, you can see the flat grains all lying pretty uniformly in the right orientation. I can't figure out how.

Mustafa Umut Sarac
06-29-2013, 03:38 PM
With a tabular grain emulsion, how do they get the flat grains oriented after the emulsion curtain pours onto the base?

I can think only ultrasonic treatment.

Photo Engineer
06-29-2013, 04:39 PM
Here are the answers.

1. Film used to be both glossy and matte. The matte was often on the back. It helped with retouching, but interfered with scanning. So, the matte was removed to facilitate scans and allow retouching in PS (<- gasp). However, gelatin is naturally rather glossy. The matte has to be added, and should not interfere with grain.

2. T-grains lie flat naturally due to the settling or packing process as the gelatin dries. However, the gelatin must be flexible enough for the film to turn corners in MF cameras so that the gelatin does not crack and the t-grains do not crack. Either one can hurt the film image badly.

PE

Jim Taylor
06-29-2013, 08:01 PM
Great thread, I'm following this with interest.

I have a bit of a long-winded question based on this point: in the world of B&W, the faster the film, the longer it is developed to realise the speed.

So, to prevent overdevelopment of the slower, top (yellow) layer(s); is any kind of restrainer added to the emulsion for this layer? Or, do the bottom layers contain an enhancer to increase the speed (time) at which they develop? Either option would allow the layers to develop concomitantly to the same degree.

My problem with this is that over time, the concentration of the restrainer/enhancer diffusing out of the emulsion and into the developer would increase, thus altering its performance (compensated for by replenishment, or chemical quenching by another developer additive?)

Or, are the faster, lower layers deliberately under-developed and compensated for in other ways e.g. the chemistry of colour papers and/or the orange film mask?

Or, is it too minor a problem to worry about in a 3:15 dev time and I'm over-thinking it? :)

Note to self - need a copy of Bob's book...

Michael R 1974
06-29-2013, 09:57 PM
Here are the answers.

1. Film used to be both glossy and matte. The matte was often on the back. It helped with retouching, but interfered with scanning. So, the matte was removed to facilitate scans and allow retouching in PS (<- gasp). However, gelatin is naturally rather glossy. The matte has to be added, and should not interfere with grain.

2. T-grains lie flat naturally due to the settling or packing process as the gelatin dries. However, the gelatin must be flexible enough for the film to turn corners in MF cameras so that the gelatin does not crack and the t-grains do not crack. Either one can hurt the film image badly.

PE

Wow, this is really surprising. I wouldn't have thought the individual grains would have enough mass relative to the viscosity of the gelatin to "settle" in a flat orientation. I figured they'd end up randomly oriented without some kind of intervention (not that I would have had the slightest idea how you'd do this other than the application of some type of "field").

Regarding the overcoat sheen, are you saying we have digital to blame for TMax films having a shiny emulsion side?? :mad::mad:

Ilford Delta (for example) has a matte emulsion side. Acros has a similar emulsion sheen to TMax.

Photo Engineer
06-29-2013, 10:23 PM
Many answers to many questions. Yes, digital is partly to blame for the sheen, which does not bother me! Yes, the grains orient themselves in the direction of flow which is through the hopper, and thus they are parallel and flat!

Jim, yes, there is a deveopability differential from top to bottom. Part of this is controlled by the Iodide and Bromide in the emulsion and part from both of these in the developer. That is why I have been so vocal in complaining about home brew C41 developers. If you get it wrong, you suffer consequences. There are several restrainers in each layer plus the DIR couplers which adjust development rate. The complete formula for Portra film is given in a patent, but OTOMH, I cannot remember the number nor the inventors. As one who worked on Gold 400, I can assure you that this question is not trivial and is at the forefront of our minds. You use ballasted restrainers and accelerants to achieve a proper rate so that all layers end up at the right point at the right time. This is why I avoid push or pull process. I over or under expose instead.

This question also is the reason why I complain when someone says they can do C41 at 20C or some such. It just does not work right. BTDT!

Maybe I should write Volume 2 of my book and include a complete workup of a color system! :)

PE

Tom1956
06-29-2013, 10:33 PM
Reading this almost causes me to regard rocket scientists as [...] in comparison to the film technology. Cupertino seems a building full of monkeys. I had no idea. This is chemistry folks, in it's full glory. Mind boggling.

Michael R 1974
06-29-2013, 10:41 PM
Many answers to many questions. Yes, digital is partly to blame for the sheen, which does not bother me!

PE

Ha! It bothers some of us when we use glass carriers and get Newton rings on the emulsion side! - which I still haven't figured out how to get around! It's a fairly well known issue with TMax and a few well known names gave up on TMax for this reason.

Photo Engineer
06-29-2013, 11:37 PM
Michael, there are many solutions to your problem. One, suggested by EK years ago was to use Opal glass which is frosted and prevents Newton rings. Also, there are methods to prevent them.

Even in the most critical applications, we did not find glass carriers significant. In fact, oil immersion carriers with glass were of more use. We had some contact with that as far back as 1962 when I was at Cape Canaveral.

Also, with a mixed workflow which includes scanning (the most significant change yet) this helps imaging. So, there were solutions and tradeoffs. It seems to work for most.

PE

akulkis
06-30-2013, 03:35 AM
Reading this almost causes me to regard rocket scientists as [...] in comparison to the film technology. Cupertino seems a building full of monkeys. I had no idea. This is chemistry folks, in it's full glory. Mind boggling.

Yes, by comparison, rocket science is comparatively easy. It's mostly plug-and-chug mathematics, but very little in the way of creativity unless someone's trying to do something significantly different.

Photochemistry...every chemical added adds a possibility of unintended interactions... think of the growth rate of the permutation function P(x,y) and the combination function C(x,y) as x and grow. So to minimize a side-effect.. you can add another chemical.. oops, now you've just increased x yet again.. or figure out some other way to shunt the effects of the side effect to a negligible amount.

Mustafa Umut Sarac
06-30-2013, 11:34 AM
Michael,

When I was using a huge Crossfield Drumscanner , I was using a British made anti Newton ring spray. Vaseline is another way. And the oil immersion but its messy.

Photo Engineer
06-30-2013, 11:45 AM
Well, in rocket science, you cannot easily do factorial experiments. In photo engineering it is quite common.

PE

wildbillbugman
06-30-2013, 02:43 PM
I have a good friend who was a "rocket Scientist", back in the '50s and '60s. Back then at least, it was anything but "plug and play" In every field, From Rocket Science to short order cook, it looks easier than it is.
Bill

Michael R 1974
06-30-2013, 08:13 PM
Well, frosted glass below the negative is not a good idea. As for wet mounting/oil emersion, this is a last resort at best, not something anyone would want to have as part of a normal workflow. I've tried a number of coated/thin film optical glasses in an effort to get rid of Newton rings when they occur on the emulsion side of TMax. Since it is an intermittent problem, it is difficult to say with certainty but I'm pretty sure none of them worked. The "best" solution I've found is to use a sheet of unexposed, fixed Tri-X 320, which has just enough "tooth" on both sides. But in the end, better off using Ilford. It's a shame since TMax 100 and 400 (TMY-2) are unique films. I had naively assumed there was something about the film that meant the emulsion overcoat had to be glossy. Now that I know it was simply a compromise in ease of analog workflow for the sake of scanning quality, I don't feel quite as bad about dumping them.

Photo Engineer
06-30-2013, 08:26 PM
Well, Michael, I have made enlargements of up to 16x20 from both 120 and 4x5 negatives without a glass carrier and they are quite sharp. Some of them are on display here at our mall at the instruction center. I can understand that some people have preferences, but I seem t be able to get along without glass. We did at EK as well in most cases. They used liquid filled glass carriers for 30x40, but that was more for scratch elimination.

However, this is far from the intended topic in some ways.

PE

Michael R 1974
06-30-2013, 09:51 PM
Point taken - apologies for the digression - but I'm happy to have learnt a few more things about making film anyway :)