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Writer / Ed Buffaloe
Photography / Ed Buffaloe

Less is More

Ed Buffaloe explains how to make an enlarged negative for contact printing by reversal.

The factor that most often inhibits people from trying the historic photographic processes is the need for a large negative suitable for contact printing.  The traditional means of obtaining an enlarged negative has been to make an enlarged film positive (known as an interpositive) and then make a negative by contact. The length of the process defeats many people before they ever begin.  I was pleased to discover a much simpler method in Liam Lawless' Enlarged Negatives by Reversal in issue #2 of Post-Factory Photography.  A revised version of Liam's article is available on the web at http://rmp.opusis.com/documents/reversal4.pdf.  I strongly recommend reading Liam's articles.  I am also indebted to members of the Austin Alternative Process Group for their invaluable assistance in learning this method.

The technique uses lithographic film, which is relatively cheap. Liam recommends Arista APH ortho/litho film, and I have been quite happy with the results I have obtained with it.  It is available from Freestyle in Los Angeles.

How Reversal Works

The reversal process for making copy negatives is described in Photographic Facts and Formulas (by E.J. Wall, Franklin I. Jordan, and John S. Carroll), published by Amphoto. The technique is relatively simple and is essentially the same as that used for black and white motion picture film. The film is first developed normally--all exposed silver halides are converted to silver.  But, instead of fixing the image at this point, the developed silver is removed with a non-halogenating bleach. What remains is unexposed silver halide.  This silver halide is then re-exposed under normal room light and developed, producing a reversed image. No fixing is necessary, as there is no further halide to be removed. The primary difficulty with this technique is controlling contrast--special reversal films were often recommended which are no longer available.

Single Exposure		After Bleaching and Redevelopment
Black represents developed silver. Grey represents undeveloped silver halide.		White represents clear emulsion. Black represents developed silver. Silver image is thick, producing a high-contrast image.

Flashing to Control Density

Film contains much more silver halide than is necessary for a continuous-tone image, most of which is removed during fixation. If one gives an exposure suitable for producing a normal positive image from a negative and bleaches away the silver after development, the remaining halide will be too thick and the reversed image in turn will be far too dark and contrasty for most uses. The trick for obtaining a usable continuous-tone copy negative is to increase the initial exposure, then give an additional overall flash exposure to increase the depth of the latent image.  After the film is developed and bleached, the remaining layer of halide will be relatively thin and will produce a clean continuous-tone image when exposed and developed. The flash exposure controls the high value density of the copy negative. More exposure produces increasingly less density in the final negative.  Liam Lawson has told me that he came up with the idea for the flash exposure because Judy Siegel (of Post-Factory Photography) needed a low density negative for gum printing. Without the flash, the resulting negative was too dense for her use.

Liam recommends using a 15 watt bulb, mounted on the ceiling and connected through a rheostat, for making flash exposures, but in his correspondence with me has also noted that he had to recalibrate flash times when he changed bulbs. For this reason, I prefer to use the enlarger lamp for the flash exposure. While it is necessary to dismount the negative and stop down to flash, one is always assured of an exposure that is in the correct proportion to the base exposure.  On the other hand, Liam's method is faster if you have a lot of negatives to make.

Base Exposure + Flash Exposure		After Bleaching and Redevelopment
Black represents developed silver. Grey represents undeveloped silver halide.		White represents clear emulsion. Black represents developed silver. Silver layer is thin, producing a continuous-tone image.

Initial Testing

To calibrate, perform the following three tests.

1. The first test is to determine the correct exposure for a film positive. Use a negative of normal density and contrast.  Start with the enlarger lens at f/8 and make a series of exposures at 1-second intervals. If the correct exposure proves to be too short (less than 5 seconds), either make another test strip at .5-second intervals, or stop down to f/11. Other options are to use a neutral-density or variable-contrast filter to reduce the light output of the enlarger, or adjust the output of your cold light head. Lawless recommends choosing the correct exposure in the stop bath-- note the time from the strip that gives a normal-looking, if somewhat dark, positive image, with a good tonal gradation.  Make sure you have the desired detail in the high values. It is not necessary to fix this test strip.  This exposure controls detail in the high values.
2. The second test strip is to determine the correct exposure factor to apply for reversal processing--using the exposure you have chosen in step one, expose a piece of film at 3X, 4X, 5X, 6X, and 7X that exposure, and process by reversal (as described below--use a flash exposure of 6 seconds at f/32, or 3 seconds at f/22 for this test). Once you know the correct factor to apply, you will be able to determine the correct "base" exposure. The multiplication factor controls contrast. If you have used a negative of normal contrast, it should require a factor of 3X or 4X. If the resulting negative suits your needs, you are done testing, but if its overall density is not suitable, proceed to step 3.  Once the multiplication factor is determined, you can use it for all future negatives of normal density and contrast.  As the multiplication factor increases, so does the contrast of the resulting negative. Excellent results can be achieved from very dense originals, but very thin originals are not suitable for the process. If your test results are too dense overall, perform the test again and double the flash exposure.
3. The third test strip is to determine the correct flash exposure. The flash exposure we used in test 2 may not be suitable for the process you intend the negative for. Make a negative with the base exposure you have chosen in step 2, give it a series of flash exposures at 1 second intervals from 0 to 10 seconds at either f/32 or f/22, and process by reversal. Use a densitometer to determine the correct maximum density. See tables below for suggested maximum densities for various processes. If you do not have a densitometer, you will have to print the negative to determine if its density and contrast range are suitable.The flash exposure determines the density of the high values in the copy negative--the more flash exposure you give, the less dense the high values will be.  The flash has virtually no effect on the low values.

Once you have performed these three tests on a "normal" negative, you will only need to perform test 1 for a typical negative in order to determine its "base" exposure time. If you have a negative that is unusually dense or thin, or of very high or low contrast, you may have to perform the other tests as well.

The Reversal Process

1Expose for the base time you have determined.  Increasing the base exposure increases contrast in the copy negative.

2Remove the film, stop down 4 stops, and give a flash exposure. The flash exposure will vary, depending upon the density of the original negative and the process you wish to use the copy negative for. Remember: with reversal, less is more. The less flash exposure you give, the more density will result in the copy negative.  With our base exposure made at f/8, the flash exposure time we used most often was 6 seconds at f/32, or 3 seconds at f/22.

3Develop for 6 minutes in a standard paper developer at normal strength.  We did all our tests using Dektol (1:2), but any standard paper developer at its normal dilution will suffice.  Liam states that reducing developing time reduces contrast, but that very short developing times increase fog levels in the enlarged negative.  He doesn't recommend adjusting contrast in this way.  Remember, you are developing film, not paper--it needs to be developed fully, so that all exposed halides are reduced to silver.

4Place the developed film in a water bath for 30 seconds. Liam states that pinholes do not occur with reversal processing of lith film, but we included a water bath anyway since it doesn't take long.  You may find you can omit this step.

5Place the developed film in a 2.5% acetic acid stop bath for 30-60 seconds.  (To make a 2.5% dilution, add 90ml of 28% acetic acid to one liter of water. This is double the standard concentration for paper.)  Liam emphasizes that this bath must be fresh so as to completely halt the development process prior to bleaching. When development has been completely halted, room lights should be turned on.

6This step should take place with room lights on. Place the developed film in a bleach solution of .5% potassium dichromate and .5% strong sulphuric acid mixed with distilled water. Bleaching takes about one minute.  Do not put your hands in this bleach solution.  Handle the negative with tongs or gloves. An alternative bleach that is less toxic can be made with a similar solution of potassium permanganate and sulfuric acid. See below for formulas.

7Wash until no trace of the orange bleach remains--generally about 10 minutes in a tray with a siphon.

8Clear in a 5% solution of sodium sulfite for 4 minutes.  Agitate continuously. Liam states that the clearing solution must be fresh.  The purpose of this bath is to remove the last traces of metallic silver from the film. When we accidentally omitted this step, the copy negative was too dense and had an overall fog.  After processing in this bath, the film is clear where the developed silver was and white where the remaining silver halide is.

9With room lights still on, redevelop in the same developer solution for 5 minutes. It is not possible to overdevelop, and it is important to completely develop the remaining silver halide.

10Wash thoroughly.

11Liam Lawless states that hardening is optional but recommended. It can be accomplished by fixing in a hardening fixer, or by use of a separate hardening bath. For those who use Kodak's Rapid Fixer, you can simply mix the small bottle of hardener with a gallon of water and use it as a hardening solution.

Original Pyro Negative		Enlarged Copy Neg on Arista APH

On the left is a small detail from a 6x7 negative, representing about 3% of the total negative area--it is on HP-5+, developed in PMK. The copy negative was made on Arista APH exposed for 9 seconds, plus 3 seconds from the left and right edge of the negative inward toward the tree trunk, at F/11 and given a 3 second flash exposure at f/32. The multiplication factor for calculating the base exposure was 3X.  The trunk of the tree was dodged during the main exposure. There is an overall loss of shadow detail, plus a distinct (and intended) increase in contrast on the tree trunk. Detail in the copy neg is excellent.

Additional Information

Since lith film is easily damaged by handling, I recommend leaving at least a half-inch border around the enlarged negative for manipulation with tongs or fingers. If you are enlarging only a portion of a negative, make a mask to provide a clean border for your copy.

Liam Lawless states:
"A sheet of thin black card under the film during exposure minimizes halation and avoids recording any marks or scratches on the easel."
I use a piece of photographic paper exposed and developed to total black.  The reverse side is used for focusing.

You can dodge and burn the film during the initial exposure, just as you would a print, and it will have the same effect, on the final print made from the copy negative, as if you had done the dodging and burning during the printing process.

If you are concerned about fine detail in the high values, make sure your initial exposure is adequate, and extend the initial development time.

A black tray is ideal for the clearing bath, because you can get some idea of the relative values in your image.  What you will see is a semblance of a positive image, the high values being represented by the white unexposed silver halide, and the low values by the clear areas of the film which appear black in a black tray.  In the tray, however, the image will appear to be of lower contrast than your developed-out negative will be.

The Arista APH film is dark on its base side.  Its emulsion side appears considerably lighter under the safe light.

Place the negative in the carrier emulsion side up, so when the image is projected onto the lith film it will be reversed from left to right. Later, the copy negative will be turned emulsion side down for contact printing, and so will be correctly oriented.

Orthochromatic film must be handled under a red safelight. A Kodak 1A (light red) filter should work, or a red-painted darkroom light bulb.  Electron Microscopy Sciences carries a full line of safelights and filters, as does CameraStore.Com.

Ed Buffaloe is a fine art photographer from Austin, Texas, USA and also owns and runs Unblinking Eye.

This article was published on Unblinking Eye and has been supplied with kind permission by Ed Buffaloe. Copyright 2002. All rights are reserved.

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