Surface Development

[pgomena]

I've read several items about film developers with "surface development" properties. These are staining and non-staining developers of various types.

Given that modern film emulsions are extremely thin, is there truly any advantage to - or even any effect - that can be called "surface development?" I could see an advantage to such developers for thick-emulsion films in the past, but is this a relevant, effective or advantageous tool today?

Peter Gomena

 

[Ian Grant]

Surface developers are usually Pyrocatechin based, probably the effects aren't quite as good on modern emulsions, they were supposed to work well cutting halation in the film.

Only Lucky films suffer from halation these dats.

Ian

 

[Paul Verizzo]

Here's a good article on physical development.

http://unblinkingeye.com/Articles/Physical/physical.html

Suddenly I keep hearing Olivia Newton John in my head.........

 

[gainer]

The term does not apply to the surface of the emulsion but to the surface of each silver halide crystal. All our films have those. The discussion of the virtues pro and con would be too long for here.

 

[Photo Engineer]

A slowly diffusing developer can also be a "surface" developer meaning at the surface of the film. Mees shows examples of differential development with heavy development at the surface and none at the base near the film support.

Dichroic fog is an extreme example of surface development.

PE

 

[Alan Johnson]

G.W.Crawley BJP Jan 1961 wrote: "Even an acid amidol 'depth' developer will give excellent sharpness and definition on modern thin films".
It may be the surface development did not contribute much to sharpness since these thin films came out in the 50's.The type of developer that has surface development also is often the type that promotes adjacency effects,it may be these are more important contributors to sharpness.

 

[pgomena]

Thanks, everyone. I was just curious. I've used PMK, Pyrocat HD, WD2D+, TFX-2, and recently saw Sandy King's article on Diafine in which it is mentioned Diafine has surface development properties. Mr. Gainer's explanation that it's not just the surface of the emulsion but the surface of the silver halide crystals that are affected is interesting. Not being an emulsion chemist it takes a bit to get my mind wrapped around these concepts, but I am beginning to get the picture.

I had read that the tanning effect of pyro developers created surface development because it hardened the gelatin before the developer could work down into the emulsion where other exposed halides might dwell, limiting their development. It would seem that Diafine, which soaks thoroughly into the emulsion and develops to completion must be more to Mr. Gainer's explanation than to emulsion surface hardening.

Peter Gomena

 

[gainer]

The effect of tanning is surely seen at the emulsion surface even on modern thin emulsions. I have read that most developers cause that to some degree. I think I remember seeing it on D-23 negs, but it's been a while since I used that. But I have not heard or read of that effect being called surface development. The effect, I think, arises from hardening and shrinking of the gelatin by reaction products going on beneath the surface of the gelatin, or more properly, anywhere in the gelatin where there are exposed silver halide particles being reduced to silver and bromides. Surface development of the crystals is one of the attributes of XTOL that was said to give it some of its superior qualities.

 

[Photo Engineer]

Actually, the tanning effect is slow to take effect throughout the emulsion, and this is why Dye Transfer matrices were exposed through the base, so that tanning as it moved down through the film allowed a true bas-relief to for which stuck (hardened or tanned) to the support.

PE

 

[stevew]

Dilute developers.

I have seen such affects when testing Trix 35mm with HC-110 at 1:31 vs 1:63. Shot a night scene with streetlights. Developed to same CI with each dilution of developer. The 1:63 showed halation effects around the streetlights. The neg showed more density transitons around the lights (did not block as much) and rings around the lights where light was bouncing of the film backing. Interesting affect.

 

[Alan Johnson]

Another factor is that some emulsions produce adjacency effects which are much wider than others.I dont have examples for a recognised surface developer but for stand development in Rodinal 1:200 the adjacency effect is wider for HP5 and Tri-X than for Delta 100 and T-Max 100.
Is it more difficult for the developer to diffuse through the Delta 100 and T-Max 100 emulsions and does that concentrate development near the surface?Maybe this is not available information.

 

[Photo Engineer]

Another factor is that some emulsions produce adjacency effects which are much wider than others.I dont have examples for a recognised surface developer but for stand development in Rodinal 1:200 the adjacency effect is wider for HP5 and Tri-X than for Delta 100 and T-Max 100.
Is it more difficult for the developer to diffuse through the Delta 100 and T-Max 100 emulsions and does that concentrate development near the surface?Maybe this is not available information.

Edge effects (adjacency effects) are due to iodide released in film and consumption of developing agent and alkali during development. Diffusion through the film is not the culprit here, but then again, a dilute developer with low agitation magnifies whatever effect is there.

So, in the main, the effects you see are due to the emulsion itself, the coated weight of silver, and the thickness of the coating coupled with a dilute developer and low agitation.

Developer is not really concentrated near the surface so much as exchange is inhibited by low agitation.

PE

 

[Alan Johnson]

PE,
I should have said the adjacency effects I referred to were those producing light lines on the print. From Mees & James 3rd edn p521 "...enhancement of density at the edge of the dense area is known as the border effect...produces a light line on the print...can be explained...fresh developer is available not only from the surface but also from the adjacent part of the emulsion..."
The mention of developer from the the adjacent part of of the emulsion means that it arrives by diffusion. I am not saying it is true but different rates of diffusion could explain different widths of light line edge effect.
Chemical explanation you mention appears to explain the other type of edge effect, fringe effect,I did not mean to refer to this.

 

[Kirk Keyes]

So if one wanted to make a "emulsion surface" developer, one would want to restrict the diffusion of the reagents into the emulsion. Some say that tanning does this. What about using a physical property of the gelatin itself?

Design a developer that works at a low pH, perhaps even one that functions at the iso-electric point of the gelatin. That's about pH 4.8 or so for bovine gelatin like what is used in photo emulsions. This would allow the gelatin to have a small amount of swell, more than 50% less than with a developer at pH 10 or so.

Additionally, adding a salt like magnesium sulfate could help minimize swell too.

Perhaps making it a fast acting developer too to minimize development time. That would help minimze diffusion. Eveness may be an issue, but we're going for mimimum emulsion penetration here.

Perhaps someone could formulate an amidol based developer that could do this? Or a developer that uses a very large molecule that will not penetrate far into the emulsion.


Kirk

 

[Photo Engineer]

Alan;

You are correct in understanding, but with different films in the same developer it is difficult to say that what you state is going on unless you know iodide content, silver level and etc. Otherwise the emulsion can cause the differences you see.

Kirk;

When pig gelatin was used, with an isoelectric point of about 9, no significant effect was seen in films such as described. The only examples that abound are matrix film and Kodachrome, and the Kodachrome effect is from a diffeerent source. The formation of the dyes forms a relief image.

Now, it is possible that the formation of the stain in a staining developer could form a relief image and that is pretty much what matrix developer can do, but it hardens as well so it is difficult to distinguish the relief image caused in this case by hardening and by the formation of the stain.

For those who don't know of this effect, it is well known that formation of dyes in film from external materials increase the bulk of the film where the dyes form. What is not known well is whether enough "dye" or stain forms in a tanning type developer to distinguish the relief image formed from this and from hardening. From my POV it is moot as to which causes it. The problem is that for best results it should be formed from the bottom up as it is in a matrix film situation because development takes place from the top down. A diffusion front of developer is considered to take about 15" to reach the bottom of a film, but there is also an induction period before development starts. These must both be considered before understanding what goes on.

In addition, exposure is from the top down, and the turbidity of the emulsion creates a gradient effect which is difficult to separate out from the differential effect of developer. But, over a 10' develpment time, a 15" diffusion rate is hard to assign to a 'surface developer effect'.

PE