Wednesday, June 4, 2014

Film types that work best in the instant mode

Some films with cubic grained emulsions
What film shall we use, and can we use an off-the-shelf sheet film (to get started) or do we have to have one custom made?

These are important questions for New55 FILM. Polaroid used a material known as SO-139 for T55, supplied by Kodak. We know today that SO-139 is a dye sensitized cubic grained medium speed emulsion similar to Kodak's Panatomic-X, supplied in long rolls for processing.

One of the problems with old T55 was that the negative was too big: It's size was a poor fit in many scanner and enlarger carriers.  We want to avoid that.

Another problem with custom made anything is lead time and start up cost. Could be too much in our case.

A better way is to find, if possible, something already available that works well. For those of you who have been following along, we started with EFKE because their film worked great in the DTR process, and we were quite disappointed when EFKE ceased production.  I really liked it for everything: monobaths, DTR and conventional processing, but I had to get over it.  Since that time we have purchased and done experiments with nearly every available black and white 4x5 film, and we have learned a lot of interesting and valuable things about them.


Most of the cubes are near the surface,
and that's good.
Cubes and Tabs

In the days when DTR was invented and developed by Agfa, and Polaroid, the only emulsions used were so-called cubic-grained emulsions.  A cubic grained emulsion is, as the name implies, composed of silver halide grains shaped like cubes of salt, though smaller, often suspended in just a single layer of gelatin.   Tri-X is a good example of a cubic grained emulsion. It can look sharp, and grainy too.

The "tabs" are well below the surface.
Fujifim and others do a much neater
job than this picture shows.
To make a very long story short (that includes probabilistic photonic theory and advanced, multilayer coating technology), the tabular, or tab-grained emulsion was developed to overcome the graininess, yet maintain the high speed, and there are other advantages to tab grains, such as less silver used and somewhat lower cost of materials.  In order for tab grains to show their flat face to the light, which improves film speed, they ought to be laid down flat and close, like a tile floor. One way to do that is to first coat with a very thin layer of tab grained filled liquid emulsion in such a way as to get a lot of the tabs to lay parallel, and down on the surface of the film base. Then an overcoat of clear gelatin may be applied to provide durability. The result is a smoother look and less grain yet good film speed.

The flat plates need to lay flat on the film base
and this requires special coating tricks.
But there is a downside to the tab grain scheme that some of you already know about: Because the grains are well below the surface, it takes more time for processing chemicals to get in and do their job. Developing, fixing and washing all take more time with tab grains. Not enough to bother anyone - much, except anyone in a hurry, like us.

Instant photography utilizes the rapid processing of the negative and formation of the positive image. This process is slowed down by multilayered tab films, and they are not what we want right now for our New55 FILM negative.

We want the "rocks" to sit right next to our processing reagent and be available as quickly as possible so that the DTR process can proceed without delay. If you take a look at Fujifilm's FP-3000b negative, (out of production) which processes in 15 seconds, you can see the remaining silver grains with the naked eye!

Only one of Land's list of cubic grained emulsion films survives today. Note that he also experimented with papers, such as Kodabromide, as the "negative".

Land's list of films tried. In those
days they were all cubic
grained films and papers.
But there are at least a dozen remaining cubic-grained emulsions if you look around, and some of them are very close to such classics as Panatomic-X in their operation.  Each have their own advantages and disadvantages, and costs.  Logistics, shipping, and import duties also contribute to the cost and risk of sourcing the films, and then there is the reverberating market for analog films in general, which tends to rule out weak hands in the long-term.

In some respects, the cubic grained emulsions we need for New55 FILM production are simpler and more widely known than our receiver sheet! Sobering, but also intriguing: Could we make film, too? If we want to do that, as a strategic move, where would we start?  It's too soon for all that, as we are very busy with all the other things - items that are no longer made.

So we can be grateful for the likes of our existing film makers who have kept at least a few traditional emulsions alive and available, and we have learned that, in total, more cubic-grained emulsions are sold today than tab grain emulsions.

The final emulsion for New55 FILM production has NOT been set. That gives us some lateral maneuvering room as we plan the other parts of the system such as the processing chemicals, and the all-important receiver sheet design.  You can be fairly certain, however, that any film we use will feature a cubic-grained emulsion.








6 comments:

Paul Cunningham said...

It's not clear to me that tab-based grains are of a necessity farther from the surface of the film, although it seems in practice that they are.

Michael Calvert said...

Tri-x 320 is a wonderful emulsion, but how long will it remain in production by Kodak?

Bob Crowley said...

I have been told that HP5+ is Harman's best seller which competes with Tri-x. I cannot guess if Alaris will keep Tri-x alive or not. Harman is in position for the longer term. Tri-x is the best selling film of all time, according to Kodak.

Brandon said...

What about Double-X still made by Eastman Kodak motion division? They could do a special order item.

Bob Crowley said...

XX can be processed in a monobath. But the largest size it is available is 35mm, so, too small for New55 to consider. It appears to me to be Tri-X.

Gene McCluney said...

"IF" Kodak still makes XX, then there are master rolls of it that are quite wide. Film is not coated on a narrow 35mm size base. It is slit and perforated to that size. Therefore if there exists a current master roll of XX then Kodak "could" custom cut it with some sort of minimum order. They have done this before with Tri-X in odd large-format sizes. Of course XX would be on the thinner roll-film base.