Contrast control & color printing

Dear forum,

I´m quite new to photography and so I´m just studying the basics. By those means I stumbled upon the fact that color printing paper isn´t available in so many different grades as is b&w printing paper. So there isn´t as much contrast control in this field. Can someone explain me why this is the case?
Is it because contrast can´t be manipulated that much in color as in b&w. I came thinking about that after reading another old thread so I will use the important words of the relevant post.
To adjust contrast means to make the image brighter or darker. The
only way to do that is to make the dyes thinner. This lets more light
reflect off the paper. But as a dye gets, say, thinner it removes less
of its anti-color until it finally disappears and no anti-color is
removed. And the other way around if the dye gets thicker. So the
scale doesn´t go from, say, a dark magenta to a light magenta but from
dark magenta to white. Or from a saturated magenta to an unsaturated
magenta.
The digital process can compensate for this unwanted increase or
decrease in saturation if contrast is adjusted in the luminosity
channel of lab-mode. In this case neither hue nor saturation is beeing
changed. There is a nice little example of that on
http://www.cambridgeincolour.com/tutorials/photoshop-curves.htm. But
we can´t do the same in analog color printing.
It could well be that this is complete garbage as far as the
subtractive mixing of the analog process is concerned and if so I´d be
happy if someone tells me so that I can get this idea out of my head
and can think in another direction.

Best regards!
Monica Schulz

My spin on contrast and colour printing

with b7w all you have to impat meaning after you have exposed the shot is tonality - i.e the gradation from black to white. The contrast number is the way I thing of how quickly the journey from white to balck happens.
The overall exposure - ie when to start the highlight detail, then there are the local controls of dodging and burning. alll of that has to impart to the viewer the abstraction of the original scene that black and white is.

With colour prints, well, there is the chance to manipulate, but so much more it is about the colours that you captured in the first place. and the fact that we see in colour (well almost all of use do). Yes, there is the overall tone and highlight detail, and non normal colour cast if we choose to intorsue one. There is so much more in the picture to keep our eyes busy in a colour print that contrast is not usually noticed unless it is very off from what you would expect from the scene.

There are techniques of pre-flashing, bleach and redevelop, etc to manipulate colour contrast, but for me it is usually a matter of printing to a a supra endura or portra flavour in the Kodak line. Rarely the ultra- too contrasty for me.

Unlike controlling contrast with B&W materials - manipulating mid tones - color materials are much more limited, sort of a one shot deal, what you see is what you get. Color materials have a narrow contrast range compared to B&W, but you can lighten or darken a color print across the range if you're willing to sacrifice some D-max and color saturation - when you're lightening; darkening usually results in a muddy looking print. .

Monica Schulz said:

that color printing paper isn´t available in so many different grades as is b&w printing paper.

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Correct that to colour printing paper is not available in different grades anymore.

Colour paper never was available in as broad a range as B&W paper grades, but until recently you could at least find low, normal, and high contrast papers. Kodak had the Portra-Supra-Ultra triad in their Endura line of RA4. Now they only have Supra.

I need to go back reading Ctein's Post Exposure before I can find again the suitable explanation for the dearth of contrast grades in colour printing papers, but I know it's there.

mhv said:

Correct that to colour printing paper is not available in different grades anymore.

I need to go back reading Ctein's Post Exposure before I can find again the suitable explanation for the dearth of contrast grades in colour printing papers, but I know it's there.

Click to expand...

It would be very kind of you to do so. I haven´t access to this book.

Best!
Monica

There are two contrasts to consider in color. One is color contrast and the other is image contrast.

Portra NC, VC and UC are the three 'grades' of color contrast. Gold is higher color and image contrast both. So, the films can handle part of this. The other part of this is in the paper. There is Endura Supra and Endura Ultra which give basically two grades of contrast. And, contrary to comments here, both are still available, but in fewer sizes and surfaces than previously.

In fact, Kodak just released a new version of Ultra Endura. Fuji recently released a new version of Crystal Archive as well.

In addition to all of the above, there are ways to manipulate the process to give increasing grades of color, but this is much more complex. If you want more informaion just let me know.

PE

Photo Engineer said:

There are two contrasts to consider in color. One is color contrast and the other is image contrast.

Portra NC, VC and UC are the three 'grades' of color contrast. Gold is higher color and image contrast both. So, the films can handle part of this. The other part of this is in the paper. There is Endura Supra and Endura Ultra which give basically two grades of contrast. And, contrary to comments here, both are still available, but in fewer sizes and surfaces than previously.

PE

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Yes, I´ve seen that on the Kodak website and all are very contrasty, far in excess of ci 2 I guess. Why are there no papers of about 1,7 like in b&w?

Photo Engineer said:

In addition to all of the above, there are ways to manipulate the process to give increasing grades of color, but this is much more complex. If you want more informaion just let me know.

PE

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Some sources I read mentioned the possibility to develop the negative different from the manufacturers standard to change the contrast others state that this would lead to twisted curves and incorrectable color shifts. Because I have no practical experience I don´t know weather it´s true or not. But my main question is what happens to the color if we apply a different curve in print making. We change the density of that color in the print and as far as I understand that should change it´s saturation and not it´s luminance. - Is that what you mean by saying " increasing grades of color"? Is that correct?

Best!
Monica Schulz

Monica;

The "grade" of Endura Portra paper is about 2.0 in the mid scale. Portra NC is about normal grade in contrast and color, so this combination would be a "normal" grade of color and contrast both. There is no lower grade than this, just higher grades. All methods I know of increase the effective grade or the color saturation.

Methods applied to film will generally ruin the negative, but methods applied to paper can be varied from sheet to sheet to get different effects.

However, if you truly wish lower contrast and saturation, try adding about 1/2 gram to 1 gram / liter of Sodium Sulfite to the color developer (RA-RT color developer replenisher). If this is not enough keep going up and contrast, saturation and dmax should go down. Another such aid is Citrazinic acid added to the developer at about 1/2 gram per liter. That is about all I know that can do the trick to lower contrast and it is a rather poor set of options IMHO.

Sorry, but the goal (resulting from complaints) has been to get normal or higher contrast.

Two last thoughts are to get some Vision motion picture film, shoot as normal and have it processed as normal and then you print it instead of the lab. The Vision film family are 1 grade lower in contrast than the Portra films for use in Motion Picture films. Printed on Endura, they will therefore be 1 grade lower in contrast. The other thought is that you might want to make a contrast mask to lower contrast.

PE

Photo Engineer said:

Monica;

The "grade" of Endura Portra paper is about 2.0 in the mid scale.

PE

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Is this a "gamma" value or a "contrast index" value? As far as I understand both do differ and ci is lower than gamma.

Photo Engineer said:

Portra NC is about normal grade in contrast and color, so this combination would be a "normal" grade of color and contrast both. There is no lower grade than this, just higher grades. All methods I know of increase the effective grade or the color saturation.

PE

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So we agree that higher contrast raises the saturation. And that´s my point: If the contrast increase would work correct, it should raise the brightness (or luminance or value) of a color and not it´s saturation, wich is another dimension of that color. So the statement I found in another old post seems to be correct: "... That´s why black and white is a better medium - it works right. It´s also why most color pictures can never look quite right. The highlights on the apple aren´t brighter red, they´re pink or white. Only a dark apple gets to keep all it´s color".

Photo Engineer said:

Methods applied to film will generally ruin the negative, but methods applied to paper can be varied from sheet to sheet to get different effects.

PE

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So it´s correct not to alter the development of the negative.

Photo Engineer said:

Sorry, but the goal (resulting from complaints) has been to get normal or higher contrast.

PE

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Yes, I read about those studies conducted by Kodak several decades ago that lead to the conclusion that most people prefer a slight contrast increase in the mid-values.

Best!
Monica Schulz

First off, image contrast is not equal to color contrast or saturation. In fact, due to the way color films are constructed, these can be mutually exclusive, that is you can have a high contrast material with low color saturation and vice versa. So, higher contrast does not have to raise the saturation. Saturation has to do with the purity of a dye, not with the rate of change of density with exposure. The latter is contrast.

Endura Supra has a nominal 'grade' of 2.0, but a mid scale straight line contrast of about 2.5. This is defined by ANSI standards as being 'normal mid range grade'. Or whatever..... In any event, as you see, CI is lower than gamma.

You should not alter the negative, it is not a very good thing to do. It is best to work with the paper.

PE

Well, I think you got a much better answer than I could uncover, so I will leave you in the hands of the pro.

Ultra not discontinued? Blimey, I'll have to tell that to my local knuckleheads...

mhv said:

Well, I think you got a much better answer than I could uncover, so I will leave you in the hands of the pro.

Ultra not discontinued? Blimey, I'll have to tell that to my local knuckleheads...

Click to expand...

I've seen the Kodak web page.

PE

I have lots of experience with controlling contrast. Here is my two cents worth.

You can control contrast by altering the development of C41 film for some films just like you do in b&w without color crossover contamination between the RGB layers. I use Portra 160 VC and Kodak C41 chemicals and here are my brake downs of development times.


Developing the film for longer periods than 3:15 only increases the overall density and grain of the negative and does not increase the contrast of the film. In other words, the slope of the characteristic curve (CC) moves up vertical, but does not increase in angle. 3:15 is the industry standard time and will yield the highest contrast and color saturation possible. It also has a dynamic range of around 10 stops out of the box. The movie industry drives this time. As you underdevelop the film both the color saturation and contrast will be reduced, but because the CC is so straight (and perfect) the dynamic range will increase as well. With careful development you can squeeze 14 stops out of the film. I use no graduated neutral density filters because the dynamic range is very close to the human eye (14 stops). I have images with good detail in both the deepest crevices of the shadows all the way up to full detail in those brilliant white clouds. In fact, my developing methods allow me to capture detail on film I cannot see with my own eyes. At N-2 reds in the shadows will turn a muddy brown. I uses 2:45 as normal development because it produces a softer negative which is a lot easier to print. When I shoot in even flat light I will develop the film at N+1 or 3:15.

I use Fuji Crystal archive super type C paper. The contrast and color saturation is extremely high and will more then compensate for the reduction in color saturation when you underdevelop the negative. Most people believe I use Cibrachrome because of the colors in my images. When I tell them that I use color negative materials they cannot believe it. The paper is also very difficult to print with because of it's steep CC which is why I use 2:45 as my normal development time. I use my own proprietary methods for controlling paper contrast with special masks and composites that have taken me years to develop. You can also control contrast using Howard Bonds method for producing unsharp mask for b&w and adopt it for color negatives with good results.

From my experiences, I have found that contrast and color saturation are very closely linked together. Increase the contrast of the film ( increase the slop of the CC) and you get and increase in color saturation. Likewise, decrease the contrast of the film will result in a decrease in color saturation as well. This relationship has to do with the slope of the film's CC. For example, color side film has a dynamic range (DR) of are 3.5 to 4.0 stops. Its CC has an extremely steep negative slope compared to color negative film, and because of this, when you change the exposure with many color slide films by a 1/3 of a stop you will get a huge jump in density which has a very noticeable effect on the image. The large density increase also increases the color saturation because there is more color dye imbedded in the film's density delta change of 1/3 stop. This is why color slide films have a higher color saturation than color negative films and is more sensitive to changes in small exposure.

A 1/3 of a stop change on a shallow CC for color negative film has such a small density change you will not see much of a change in the image or color saturation of the film. By altering the developing times with C41 you change the CC slope, the delta density per unit of exposure, and ultimately the color saturation as well.

Hope this helps...

Steve;

A comment is due here. It is axiomatic from science that color contrast and image contrast can be two different things. Add yellow dye and cyan dye to magenta and it becomes desaturated but can have the same image contrast. Sorry, but I have to disagree with you.

As a side note, Type C is a trademark of Kodak, as is Type R. If Fuji uses it, they do it under license from Kodak.

Over and underdeveloping film can be done, but at the risk of crossover in the curves and once that takes place, you are done as far as gettting a good image is concerned. You are right to the extent that there is a contrast shift up or down, but also the speed changes as you push or pull the process. I have done both and gotten good results, but it is best to play with the print, and that generally can be done only to increase contrast due to the way color materials are made.

PE

Hi PE,

I base my observations on applied experience which can be less precise.

I have found that Kodak Portra 160 VC film responds better to contracted and expanded development as modeled by the Zone system than many b&w films. I never had crossover problems and have excellent results even at N-2 (2:15 development times - remember 2:45 is N for me) as long as there are no significant reds in the shadows. I have built CCs for all films I have tested and for each development time I have used. God forbid I do another. I use ISO 80 for the older Portra film and 100 for the newer Portra 160 VC film across all of my development times. I strive for a slightly denser negative than AA recommends to compensate for any meter errors that occur from reading light on different surfaces. Please note, most films will produce crossover when under developing or over developing, but Portra 160 VC is not one of them.

If you change the ISO of the film as you change the development times then in effect you are trying to achieve a normal contrast (N in the Zone system) for the ISO-development combination (which is really a curd approximation of the real N). Thus, if you shoot 160 at ISO 400 and alter the development then your goal is to get a normal looking image at ISO 400 which has a normal CC slope. This negates controlling scene contrast by altering the ISO for a film development time. By holding the ISO constant over different development times you allow the film contrast to change and thus alter or control the scene contrast which is what the Zone system and this note string is about. There is a subtle difference here that most people in the color world are confused about. Each method has different goals and outcomes. One is to get a normal CC slope print using a different ISO while the other is to get a different CC slope to control contrast.

One of the beautiful things I love about Portra 160 VC is that it's CC is a perfect straight line right up to DMAX. The only other film I know of that has a straight line CC like Portra's is 100TMAX. The clarity of detail and tonality throughout its dynamic range is uniform and creamy respectively. It is an amazing film allowing you to print with full luminous shadows, and yet retain subtle detail in the high values especially in those billowing cumulonimbus clouds. The hard part is transferring all that visual information from the negative to a high contrast paper like Fuji CA type C. Once you have figured that out though, you can do some amazing things artistically, and only then will people think your prints are Cibrchromes.

I stand by applied observations with no disrespect to you PE, that both gray scale contrast and color saturation is tied to the slope of the CC. The steeper the CC the higher the gray scale contrast and color saturation. At N-2 you can produce a very flat dull desaturated image and that is because of it's low CC slope. Try it. Take a low contrast scene that is evenly light and develop the film a 2:15 and print it. It will be very obvious.

Regards...

Steve;

I can only base my limited experience on many years of coating color paper and color film at Kodak and testing my coatings quantitatively by using the full 21 step chart, spectrophotometric curves of the dyes and analytical and integral density readings.

Yes, you can over and under develop, no, they are not recommended. Color film is built to a given contrast and color saturation and is not like B&W film primarily due to diffusion problems in thick multilayers. Therefore it is designed for 'getting it right the first time'.

Gold film is built to have the highest saturation and contrast. Portra has about the same contrast in all versions with 3 color saturation levels. This can be shown via spectrophotometric curves of the dyes produced. The zone system is a poor substitute for the tools used in design of the materials.

I'm sure that you can observe qualitative 'changes' that can be misleading. It is very hard to separate contrast from the purity of a dye, just as it is hard to separate contrast and sharpness which is another area where people get confused.

This is not the venue to go into the details, but I can assure you that dye purity / color contrast is not necessarily the same as image contrast.

PE

Steve. I can't speak for others and my understanding may be wrong but I always thought that anything a couple of seconds less than 3:15 would be seriously detrimental but your experience is that as much as 30 sec less is normal and even a whole minute less for certain conditions is OK. Does this only hold true for Kodak Portra 160VC or are there other films for which these shorter dev times hold good?

From your experience it appears that erring on the short side of 3:15 will do no harm and it is erring on the long side that has the real dangers. If nothing else it would seem to call into question the need for absolute accuracy with colour neg dev compared with the prevailing theory advanced that a few seconds either way makes little difference to B&W but may ruin colour. I am sure that it is this kind of hard to achieve accuracy that may put off newbies from colour developing.

It is possible for you to post some of your 3:15, 2:45 and 2:15 shots with details of the light conditions. I admit to feeling loathe to depart from the standard 3:15 time but it would be instructive to see the effects of the other times.

Thanks

pentaxuser

Actually, if you are making a dupe negative from an Ektachrome slide, Kodak suggests you use Portra NC or VC with one stop pull to give the right contrast. This is about 2:30 - 2:45. The norm is 3:15. At greater that 3:15, contrast will go up and latitude will shorten. Depending on the batch of film, you can begin to get crossover at higher densities with longer development times or shorter development times. The reason is that the release process is 3:15.

PE

There was a series of articles in The Darkroom magazine back in the 1980's about controlling contrast in both film and paper processing. The technique if my memory serves me correctly was latent image bleaching and development. No special chemicals involved all standard stuff and did not suffer from color crossover. I think I still may have copies of the magazines buried somewhere. Will see what I can find.

Not sure if this technique would work with today's films or papers - but you never know until you try

Mike

Sterry & C41

.1 percent solution of potassium ferricyanide and water with .03 percent potassium bromide to control fog. 9 minutes at 74 degrees. Discard after one use. Was also used with RA4 papers.

I have the article somewhere and can look it up if anyone wants. I actually used this on a roll of Fuji 100 last night, though I used it at 90 degrees and for 5 minutes. It works, but I've not printed the negatives yet, so I don't know about any obvious crossover problems. Rate the film at 1/2 the ISO when shooting it.

Bill;

The ferricyanide added to developer will instantly be reduced to ferrocyanide with oxidation of an equiivalent amount of developing agent. You did not give the volume of your solution, but this reduction in the amount of developing agent can be accompanied by severe stain due to the oxidized developer reacting with the couplers in the film or paper. It takes some time for the oxidized color developer to dissipate, and it uses up sulfite as it goes, so that is another effect.

You could totally blacken a sheet of RA paper by going from the developer into that solution of yours, in total darkness. After blixing, the paper will have a high stain or be totally black. I've done it years ago, and cannot say how dark current paper will get as both developer and paper have changed since then.

In fact, this is why a ferricyanide bleach is not and was never used directly after color development. There was always a clearing bath and wash after the developer to prevent interaction of developer with ferri!

PE

pentaxuser said:

Steve. I can't speak for others and my understanding may be wrong but I always thought that anything a couple of seconds less than 3:15 would be seriously detrimental but your experience is that as much as 30 sec less is normal and even a whole minute less for certain conditions is OK. Does this only hold true for Kodak Portra 160VC or are there other films for which these shorter dev times hold good?

From your experience it appears that erring on the short side of 3:15 will do no harm and it is erring on the long side that has the real dangers. If nothing else it would seem to call into question the need for absolute accuracy with colour neg dev compared with the prevailing theory advanced that a few seconds either way makes little difference to B&W but may ruin colour. I am sure that it is this kind of hard to achieve accuracy that may put off newbies from colour developing.

It is possible for you to post some of your 3:15, 2:45 and 2:15 shots with details of the light conditions. I admit to feeling loathe to depart from the standard 3:15 time but it would be instructive to see the effects of the other times.

Thanks

pentaxuser

Click to expand...

There is no danger to altering the development times of Portra VC. Increasing the development time beyond 3:15 will gain you nothing other than a denser negative, more grain, longer print exposures, and less sharp images simply because the negative is thicker. The slope of the CC remains the same above 3:15, and thus, the scene contrast will not be altered for development times greater than 3:15.

It has been three to four years since I have tested other films. At that time I found many films did experience crossover when the development times were altered. I have since latched on to Portra VC 160 which responds very well to controlling contrast through contracted development down to 2:15. As I noted in previous responses, normal development for me is 2:45 and not 3:15. At 2:45 the negative is softer, lower in contrast, has a greater dynamic range, more details in both the highlights and shadows, and is far easier to print using a high contrast color paper to beef up the color saturation.

At 2:45 the CC is more shallow and the straight line curve travels LONGER along the x-axis (which is in increasing units of exposure or latitude) to reach Dmax. The net effect of this is to increase the dynamic range of the film. For example at 3:15 the curve hits Dmax at around 11 stops along the x-axis with a dynamic range of around 10 stops. At 2:45 the curve is shallower then at 3:15 and hits Dmax at around at 13 stops with a dynamic range of about 12 stops. I build my CCs using the methods outlined in AA's book "The Negative". Of course, you need to hold your ISO constant as you alter the development times to get the effects I just noted. If change your ISO as one does with the concept of push/pull then all bets are off. Push/pull is completely different from controlling scene contrast using contracted development and holding the ISO constant.

You can develop your own CCs using the method noted in the appendix of AA's book "The Negative". First you must establish the ISO of the film. He uses an ISO that gives him a density of 0.1 units above film fog at a Zone I placement. Remember, its the shadow detail that is the least dense and most critical which is why he calibrates his films at Zone I. For color negative film you want to use an ISO that gives you a density of 0.15 for the RED layer (which is the thinest layer of the RGB layers, and thus, is most critical) above film fog at a Zone I placement. Once you determined the proper ISO for your development process then you can build your CCs and observe the behaviors I noted above. The first time you go through this process it is lot of work that is highly error prone. Once you get good at, it becomes a lot easier.

I applaud Kodak for its efforts to publish technical specifications on all its photographic materials. However, the exposure units Kodak has used for the x-axis of it CC graphs is Log exposure in Lux-seconds may be useful in the lab, but in the field it is meaningless to us photographers who work in "stops". Shutter speeds, ISOs, and aperture settings are all in variations of "stops". Lux-seconds has undermined the ability of us photographers to understand the power of color negative film and may have contributed to people switching to digital because they do not have a clue that you can get 10 stops of latitude out of the box. The reason why the movie industry shoots with color negative film is because this 10 stop latitude allows them to shoot under more adverse lighting conditions and still get great shots. This attribute alone can save them millions of dollars for making a single film. The reason I have resorted to making my own CC graphs is because of that lousy Lux-seconds. My x-axis is in units of Zones or stops and has enabled me to understand the power of film over a digital sensor which by the way has an unproductive dynamic range of about 4.5 to 5 stops at best.

Most color LF photographers use slide film because that is what everybody else does. However, slide film has a ridiculous unproductive dynamic range of 3.5 to 4 stop. If those LFers new that and what you could get with color negative film I think their preferred film would be different. Again I blame the Lux-seconds for a lot of this confusion and mismatch.

For those of you who dought my words you can go to my website at www.stephenwillard.com and take a peek. By clicking on a thumbnail you get an enlarged image along with technical data, narrative, and even maps of how to get there. The technical data will note exposure range of each image in units of stops. There is one image that is close to 15 stops from the deepest shadows to the brightest highlights. I do not use nor own any neutral density garduated filters. I have no need for them. Keep in mined that some detail is lost in the highlights and shadows while I scan the print for the website.

Please, note there are two sunset shots I did where I intentionally darked the shadows (which took a lot of work to suppress the details in the negative) to create a more graphic rendering.

I agree with Steve that a pull of development will not be detrimental to C41 processing. In fact I have just posted similar sentiments on a Fuji and Kodak film question on this forum. I don't know if overdeveloping would give much more than contrasty and grainy negatives but certainly pulling development will reduce contrast and saturation. This can be beneficial. I think the original question was though, more related to printing. Here the options are not very good. I have asked before whether any body here has used paper flashing to help control contrast in difficult contrasty negatives but only got one reply.

Sterry and C-41

The Darkroom & Creative Camera Techniques Annual Special #6, which was published in 1992 contained an article titled "Lowering Contrast in RA-4 Color Papers, Latent Image Bleaching" by Bertram W. Miller. Miller described the "Sterry Method" or "SLIMT." He indicated that he had used it with both RA-4 paper and with C-41 film. Obviously this was many, many versions of both paper and film ago. But I did try it the other night and with the Fuji 100 ISO color negative film, it apparently works very well. Miller indicated that the method would cost you about 2/3's stop of speed of the film, and so I just shot at 1/2 the ISO of 100 to be sure. His method gave the C-41 film a bath in the bleach before going into the developer, and he used a 9 minute bath at 74 degrees F. I wanted to be closer to the target of 100 degrees in order to have my film and tank up close to the normal temperature of the color developer, so I tried 5 minutes at 90 degrees F for my first try. I am very satisfied with the amount of bleaching that took place with the 5 minutes and 90 degrees. However, I do eventually want to have the bleach bath at 100 degrees also.

Now, I had also shot a roll of Kodak 200 ISO color negative film, and I shot it at ISO 100. Both the Fuji and the Kodak were developed in the same tank at the same time. The Kodak suffered TOO much bleaching, although the resulting negative was not as bad a negative as the last ones I got from the drugstore processing here in town. So anyway, the Kodak film will take more experimenting, but I feel like it will do just as well as the Fuji. I'm sure that the dilution and time in bath would have to be determined for each type of film you wanted to use it with.

I printed three of the negatives from the strip of Fuji last night, and I didn't see any obvious color crossover with the subject matter I had. I only printed one of each of three scenes though, and I didn't attempt to absolutely nail the color correction as I didn't have a lot of time to print them. I think that they looked very good but needed about 10 units of magenta and yellow taken out.

I've not yet tried the bleach on RA-4.

Bill;

You talked about adding it to the color developer. Ferri will bleach the latent image if the film is 'bleached' in it before development and if the film is well washed before development. This is well known for both color and B&W films.

Adding it to the color developer would probably have little effect as the ferri would vanish almost instantly resulting in ferrocyanide as stated above.

Steve;

My comments above were fully supportive of what you say, that both a push and pull can be applied to color film, but you must be careful with a push as some films are subject to crossover. You have to be careful of your exposure, as speeds and contrasts both can shift in a way that is unacceptable. Once you have a ruined negative, that is it!

I think this goes to show though that there are more ways to increase contrast than decrease it. The best way to decrease it is to coat lower silver, and then process in such a way that you achieve the various contrast values. I have done this and amplified the images over a wide contrast range.

I have to say though that I have not seen the slope remain constant though above 3:15. What I have seen is higher contrast and higher fog. And, each film behaves differently.

I would have to say to all of you that only by doing side-by-side comparisons and comparing the actucal curves can you be sure of what you actually are getting. Otherwise you can be fooled.

PE