Dispelling some of the Myths by Andy Cross

Dispelling some of the Myths by Andy Cross

 When you consider the number of intervening variables that can come into play between pressing the shutter button and the final print or photograph it is a miracle the process works at all let alone as well as it does. In this regard digital capture and inkjet printing is not immune either. 

I have also noticed that when a group of photographers sit around a table or camp fire and talk photography you find that just about everyone has a pet procedure, developer or means of achieving a desired result. The reason this happens is because they have created a workflow that minimizes the number of these variables and allows them to control those that remain to fairly close tolerances. 

In most cases photographers don’t know how these processes work, what developers actually are or how light sensitive emulsions respond to light. It’s a bit like driving a car. You don’t need to know what is under the hood or how it works to drive it and arrive at your destination. However when the vehicle breaks down on the Strezlicki track it becomes quite handy to know what the likely problem is and how to solve it.

It’s the aim of this article to enlighten photographers to some of the things photography has under the hood which may help in solving some of those unexplained mysteries of the 4th kind.

Emulsions are essentially silver halides. They are made by combining metallic silver with halides. The halides are fluorine (F) Chlorine (Cl) Bromide (Br) Iodine (I). These silver halides are photoreactive compounds. In short when struck with the required minimum amount of light ( photons ) some electrons fly off. This creates a minute deposit of silver at a critical spot in the affected silver halide crystals. This spot is known as a sensitivity speck. This is a deliberate structural flaw engineered into the silver halide crystal. 

This deposit is increased in size through the action of development. Developers are really just oxygen scavengers, which is the main reason developers don’t keep very well. { If you lower the energy level of unused developers by freezing them it will extend their shelf life almost indefinitely } They reduce the silver halides that have been exposed to black metallic silver through a process known as infectious development. 

Most films consist of a combination of silver bromide and silver iodide referred to as ido-bromide emulsions. This combination, according to information I obtained from emulsion chemists working at Harmen Tech and Kodak , work the best in combination with the various sensitizing dyes to produce the panchromatic films we are accustomed to. They also offer the most flexible physical and chemical ripening properties. 

Gelatin silver papers are often pure silver bromide or a combination of silver chloride and bromide, called chloro-bromide, while the contact printing papers are just silver chloride. The most light sensitive and therefore fastest silver halides are the bromides and iodides. The chlorides are the least sensitive. Occasionally some papers will incorporate some silver fluoride. But because fluorine is so reactive it is rarely used in photography.   

Most of the pure bromide papers today are graded papers and there are only a few manufacturers still making them. What these various papers offer the photographer is the means of creating different dichroic effects within the emulsion. We have all heard the terms of cool tone, neutral and warm tone images. My question to a lecturer whilst studying at the QCA many years ago is how can black metallic silver have any colour associated with it.

His reply was it’s all dichroic so research that. As an optical engineer I had made many dichroic filters and knew how they worked. Essentially a transparent medium is coated with various types of metallic salts in the correct order just the right number of wavelengths thick.

So in the case of a red dichroic filter the majority of the blue and green wavelengths are reflected or bounced off the surface of the filter and only the red wavelengths allowed to pass through. The angle of incidence will affect the colour the filter reflects and transmits. This is why they are not used on the camera lens.

These are the same type of filters used in subtractive enlarger heads which are of course the yellow, magenta and cyan filters. So how does the dichroic effect happen in a gelatin silver photograph. Light passes through a transparent medium, (the gelatin) then through finely divided particles of a metal, (the silver) reflected off the white paper base and passed through the silver particles again, at a different angle and then viewed by us. 

The photograph resembles a dichroic filter in many ways. The different colours are affected by the different way the silver grains clump together. This can be altered by starting with different silver halides, the thickness of the emulsion and by reducing them with different developers. All these variables will alter the shape of the silver grains and clumps. A bit like no two snowflakes are the same. These silver clumps or clusters will also tone differently further altering the end result.

When it comes to toners there are really four types. All gelatin silver photographs should undergo toning. Silver is a fairly reactive metal and even when the images have been thoroughly washed they still need some protection from the environment. Some photographers have told me I have prints that are 30 years old , not toned and they are fine. 30 years is only an eye blink. They can and probably will change left untoned in the next 30 years. It also means that the environment they have them stored in hasn’t caused any damage. Once they leave that environment all bets are off.

Toners fall into four categories. There are the conversion toners like selenium and the sulphide toners, sepia and polysulphide, which convert the silver to salts of silver. Namely silver selinite and silver sulphide. These silver salts are not neutral in colour and when combined with different papers the dichroic effect can range in colour from yellowish browns through to deep chocolate and purple browns.

Fig#1 This image was toned to completion in a hypo alum toner. This, in combination with a warm tone paper, is capable of producing a deep chocolate brown. This toner has to be made by the photographer as it is no longer available.

The second type are known as encapsulation toners such as gold and platinum. These noble metals essentially coat or encapsulate the silver grains creating a protective barrier between the silver and the aerial pollutants. Extended gold toning will often create a blueish black in the photograph. Normally little colour change will occur when using platinum toner.

Third on the list there are the dye mordant and chromogenic toners. The only reason for using these toners is to change the colour of the photograph. Of the two the dye mordant toner is the most stable. It involves the same chemistry as that used in making a dye transfer print. In this case the silver is bleached out with a re-halogenating bleach that has a mordant added before it is redeveloped with a developer containing a suitable dye. Often latex friskets are used to protect areas of the photograph from being toned.

Fig#2 I made two versions of this print. One was a dye induction print which involves printing a dye transfer into a silver gelatin print. This one was the test print made using the same dyes in a dye mordant toner.

This process is known as selective toning. The chromogenic toners simply replace the silver with a dye deposit which is the same chemistry as used in RA-4 printing. This does not offer any protection to the photograph at all. In fact it means the print can now fade as quickly as an RA-4 photograph.

Another type of toner which should make up the fifth category is the catalytic or metalliferous toners. Very little information is available on the web or anywhere else on these toners. I only found out about them from a friend, the late Morry Bard, who was a chemist and dye transfer printer. They should be called silver replacement toners because that is what they do. The silver is replaced proportionally with a metal of your choosing. To do this is complex and involves a catalyst. It also makes use of some nasty chemicals. But if you want to replace the silver in the image of the brass tap with brass then it can be done.   

Fig#3 Another toner that little is known about is the catalytic toner. To the best of my knowledge it has never been available in kit form. Here the silver making the image of the brass tap was replaced with brass, Gold toning was required after to prevent it from tarnishing.

But getting back to the films and papers themselves you will find that papers have a speed point just like films however none of the manufacturers ever quote an ISO for their paper products. My sensitometric testing has revealed the slowest papers are around 20 ISO whilst the fastest are around 200 ISO. The warm tone papers containing larger amounts of silver chloride are the slowest while the ido-bromide papers are the fastest. 

They also suffer from reciprocity failure just as films do. Reciprocity failure is a time v light intensity issue. Although the correct definition for reciprocity failure is rather long winded it essentially means the longer the emulsion is exposed to light the less sensitive it becomes to it. A reciprocity response can be calculated from an emulsions  slope factor. Once upon a time Kodak put this factor on boxes of chromogenic colour paper. Early production runs of DuPont, Actinia and Argenta silver gelatin paper also had it printed on the boxes. 

I won’t go into the method used to calculate the reciprocity point when you can get all this sort of material on line however once you find where reciprocity for your paper occurs you will be able to determine the increased time required when you have to burn in a pesky highlight. You might estimate the region needs an additional 1 stop increase in exposure but this comes up short. You finish up using two stops or more. In instances like this it is probably reciprocity failure causing the problem.  

Under my particular conditions and by that I mean, type of enlarger, light source, colour temperature of the lamp, lens etc, regular Ilford MG FB paper runs into reciprocity failure around 40 seconds of exposure. The slope factor tells me I need to increase the exposure by 60% over and above the time difference between 40 seconds and what I need to print it at. For example the exposure time needs to be 50 seconds. 

The difference between 40 seconds and 50 seconds is 10 seconds. 60% of 10 seconds is 6 seconds. So the actual time needs to be 56 seconds in order to get your full 50 seconds worth on the paper. By taking this slope factor into account, even if your determination of having to burn in 1 stop was incorrect, you still know you burned in 1 full stop. 

This issue becomes increasingly worse as the exposure times get longer and longer. In some instances it is better to open up the lens aperture which shortens the exposure time often getting the printer out of reciprocity failure. I am often asked why use such long exposure times to begin with. My average exposure times are adjusted to be around 20 to 25 seconds. This basic exposure time is determined from  the minimum time required to produce maximum black from the film base fog density of my negatives.

This is sufficient time not to be close to reciprocity failure but enough time to facilitate dodging and burning in. It’s difficult to get a dodging tool or burning in card into the light path and get an even distribution of light when the base printing time is 10 seconds. and you want to burn in ½ a stop. Although I’ll have to admit these days if a negative needs dodging or burning in I will bite the bullet and make a silver mask.  

Masking brings the density range of the negative into line with the printing density range for the materials being used. So you just finish up making a single exposure on an appropriate paper grade. I have written a book printed as a press ready PDF document on these processes for both analogue and digital techniques.

Here are some interesting facts related to the reciprocity characteristics of films. The older style films whose tone curves match those of Fig#4 will suffer from reciprocity failure sooner than those with tone curves that look more like those in Fig#5.  Films like Ilford Pan F, FP-4, HP-5, Kodak Tri-X etc have tone curves that match those in Fig#4 When the toe of a films curve is longer and more gradual as it rises onto the straight line portion the more prone it will be to reciprocity failure. 

Fig#4 This tone curve is typical of the older style of films. Relatively long toe with well rounded shoulder. Anyone who has plotted these curves in real life will know they never look as pretty and manicured as this.
Fig#5 This is a typical tone curve from a more recent emulsion. Practically no toe with a short abrupt shoulder and longest straight line portion as possible.

However there are benefits to using films like these. They are more tolerant to the effects of under or over exposure. With a more rounded less abrupt shoulder they are also more tolerant to over development. Which means although you will still be dodging the shadows and or burning in the highlights the information will still be there to extract from the negative. 

More modern emulsions like T-Max, Delta and Fuji Neopan and Across have tone curves like those in Fig#5 They have the longest straight line portions which is where most of the important information is recorded, the mid-tones. They offer a greater degree of tonal separation. This is the films ability to record a more distinct density difference between subject areas of slightly different colours and or areas of slightly different levels of brightness.

As always you don’t get something for nothing. These films do not tolerate underexposure very well. You may be just holding onto shadow detail and with just another 1/3 to 1/2 stop reduction in exposure the information drops off the toe and you have nothing. Similarly a small increase in the gamma of development and you lose the tonal separation in the highlights and will be burning them in.

A small increase in the temperature of the developer or change in agitation technique and your there. This is why my preferred films for pictorial use is FP-4, for my slow speed film and Kodak Tri-X for my fast speed film. 

As a matter of interest T-Max 100 ISO film was originally manufactured as a colour separation film. Its longer straight line portion is what is desired in a separation film. Before it was released researchers created the T-Max developers made specifically for this film making it suitable as a pictorial film for in camera use as well. At this time the film called Super XX was discontinued which was a film primarily used for making colour separations. 

Panatomic X was also stopped being produced a short time later which T-Max also replaced. As the Pan masking film used in making colour separation negatives was actually Panatomic X , which was coated on just one side without any anti-halation layer, meant it too disappeared. By using very dilute HC-110 developer and a spacer sheet T-Max could also be used as a masking film. Consequently Kodak made more money by covering the function of three films and only coating one.

I have been asked many times why do some of my films show mottle. Mottle is usually a sign of uneven development. Other times bromide drag , particularly on 35mm film can be seen as uneven development running down from the sprocket holes. Two different issues with two different causes. The latter is often caused by insufficient agitation. Increasing the frequency of agitation will usually correct the problem of bromide drag. This will require an alteration in development time Photographers who use the stand development technique to pull process their films may induce bromide drag. 

Mottle however has a lot to do with the surface tension of the water the developer is mixed up on combined with the format being used, i.e. 35mm, 120 or sheet film, and the processing technique. Many times photographers will prewet their films by soaking them in water before pouring in the developer. In most cases this can make the mottle worse.

That anti-halation layer on the back of the film also contains surfactants which lower the surface tension of the developer which promotes even development. That’s why the water from a tank containing a film, which has been prewet, is drained out it often has a soapy appearance. Prewetting removes the assistance it provides. 

It’s easy to test how even your development is. Point your camera at a bald blue sky with the focusing set to the lenses minimum distance. The image is as far out of focus as possible. Make a series of exposures to obtain negatives that are mid-grey. Process the film. Print some frames from the outside of the reel and some from the inner portion of the reel. Ensure the sprocket holes or frame numbers are in sharp focus. Mottle will appear as a sharp or abrupt change in density. You shouldn’t see anything but smooth continuous grey. If you do then it is almost certainly mottle due to uneven development. 

The cure can nearly always be corrected by mixing the developer up on distilled water. There are however some types of processing techniques that will produce more even development than others. You can’t beat roller transport processing for evenness in development. The processing solutions are literally squeezed into the films emulsion. The next set of rollers squeeze the old out and the next fresh lot in.

However you never get something for nothing. The tanks cannot be partially filled to save money. They generally hold several litres. Floating lids are needed for the tanks to prolong the life of the developer unless they are emptied after each use. A testing and replenishment system is required to make the machine economical. The rollers need to be kept very clean or a lot of film can be ruined.

Dip and dunk processing tanks are another option in obtaining even development. These can be fitted with nitrogen burst agitation or the film can literally be dipped in and out of the solutions. The nitrogen is an inert gas which raises the developer up and down in the tank whilst the film remains motionless. Film reels are loaded onto longer columns while sheet films are held in hangers.

Some practice is required to ensure you get the development as even as possible. Once mastered it can provide very even development and is quite economical to use. The tanks capacity need only be as large as required. Many labs who don’t run a roller system often use the deep tank system. An equivalent system is rotary film processing. These can range from the expensive Jobo auto systems through to the simple BITZ  tubes or ( Beyond the Zone System tubes designed by the late Phil Davis ). Depending on the type of system,  the type of film being processed and the rotary agitation speed used this type of processing can yield good results all the way through to disasters. 

Some systems don’t allow the developer to get to the back of the film well enough during processing. Consequently the fixed film may need to be re-immersed into a tray of developer again to remove the remains of the antihalation backing followed by rewashing.

If you’re a sheet film user there is always tray processing. This is the method I used until I installed the deep tank system. There isn’t a lot to go wrong with this method. But for consistency you really need to process one sheet at a time and only be trying to agitate one tray at a time. The interleaving technique is fraught with dangers. Scratching the emulsion with the corner of another sheet is easily done. Eliminating inconsistencies with the degree of development each sheet receives also needs a great deal of practice. Uneven development can still occur with this technique.

A different type of mottle can also be caused by replenishing the fixer over a too long a period of time. Sulphides build up in the fixer which can tone the film as it gets fixed. Subjecting any emulsion to a dilute solution of Sodium Sulphide will convert the silver to silver sulphide. When it happens during fixation it will produce a yellowish irregular stain which looks very similar to development mottle. I use fixer to within 20% of exhaustion, determined with a fixer test, and then discard. Long term replenishment I my opinion isn’t worth the savings.

Why does uneven development never seem to happen to photographic papers ? Well in actual fact it does. But because papers unlike films are always processed to completion ( with the exception being lith printing ) the uneven bits catch up. You can do a little test to prove this. Immerse an exposed print into the tray of developer but withhold one corner for 20 seconds, then continue to process the print to completion. After fixation examine the print for a demarcation line. There won’t be any. 

Can a print be over developed or over fixed ? Although development has to be taken to completion extending it too far can result in the chemical fog of the highlights. This will appear to affect the borders of the print the most and will look like it has been fogged. Fixation on the other hand can be taken too far.

A photograph needs to be fixed sufficiently to initially convert the light sensitive silver halides, which were not exposed and reduced to metallic silver during development, to silver sulphate which is not light sensitive. Fixer which is usually Ammonium Thiosulphate is a mild solvent for silver itself. Continuing fixing beyond this point will begin to bleach the silver in the photograph. 

When making final prints I use the two bath system. The print is immersed in the first fixer bath for the bare minimum time recommended. The print is then removed given a brief rinse and immersed into the second fixer bath for half the recommended time again. At the end of the printing session a condition test strip is run and the first fixer bath discarded if necessary. Print washing is another story which I will discuss in more detail when I next put my fingers to the keyboard.

When an art form has been around for over 200 years it’s inevitable there is going to be a lot of misinformation developed around it. I hope the information in this article has managed to dispel some of the myths that have always surrounded photography. 


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There are 3 comments for this article
  1. Craig Watson at 1:20 am

    Great article Andy. Very detailed and informative. Thanks to my introduction to photography at Swinburne and RMIT in the 1980s I actually understood it all. I was most interested to see your comments regarding the pre-wetting or pre-soaking of films before development. I never pre-soak my films, as I felt there was no advantage to it and it only made the entire procedure of processing a bit longer. Now I have a new reason to not pre-soak as it removes the benefits of the anti-halation layer in softening the water in the developer to provide more even development. I have often been told I should be pre-soaking the film, but nobody has been able to give me a good reason for it, other than it removes the anti-halation to prevent the colouration of the developer. Hmm. Think I’ll stick with what I’m doing. Thanks.

  2. Andy Cross at 9:16 am

    Glad you enjoyed the read. There are many more myths to de-bug but some are no longer relevant. Although I should have added the myth about push and pull processing. You don’t need to underexpose before push processing or over expose before pull. It’s about the processing only not exposure and processing. It really just relates back to the subject luminance range.

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