Processing Kodachrome as a black & white reversal film

This post is aimed squarely at darkroom aficionados.

I was given a roll of Kodak Kodachrome 40 in Super-8 format. It hasn’t been manufactured for years and conventional colour processing using the K-14 process has not been possible since 2010. Kodachrome does not contain coupled dyes so processing is not possible using C-41 (colour negative) or E-6 (colour reversal) – both of these would yield a blank film. But Kodachrome film does contain silver halide, so it ought to be possible to process it as a black & white negative.

It’s not much use to have a negative film in Super-8 format though, and a little bit of reading indicates that it should be possible to use a black & white reversal process to end up with a positive transparency film that can be projected. I wrote in detail about my motives the other day. This post is about the recipe I have devised from various sources, and that I will use as soon as the chemicals have arrived. The information about rem-jet removal I have cobbled together from various internet forums, while the information about reversal processing was mostly obtained from Ilford’s handy document about reversal processing.

Kodachrome film is coated on the back with a layer of opaque carbon called rem-jet. This needs to be removed before the film can be projected. It can be removed either before or after developing the film and each has its own advantages. Removing the rem-jet before processing means you won’t contaminate your chemicals, although it also means you have to do it in total darkness. Removing the rem-jet after processing means you can see what you are doing with the lights on, but you will probably get black residue in all of your chemicals. This is a decision for you.

First let me just copy out all the recipes needed to make the chemical baths, and then we’ll discuss how to use them. All of these recipes make 1l of each bath – adjust to suit. The baths should probably be used one-shot as the rem-jet may contaminate them even if you remove it first.

Rem-jet removal bath

1. Start with 1 litre of water
2. Dissolve 100g sodium sulfate into it
3. Dissolve 20g borax (sodium borate) into it
4. Add approx 2g sodium hydroxide to reach a target pH of 9.2. You will find some indicator paper useful.

First developer

1. Prepare Ilford PQ 1+5 (i.e. 167ml PQ concentrate, 833ml water)
2. Add 10g sodium thiosulfate

Bleach

1. Dissolve 2g potassium permanganate in 500ml water
2. Separately, add 10ml concentrated sulfuric acid to 490ml water to prepare 2% sulfuric acid
3. Carefully mix the two solutions

Clearing solution

1. Dissolve 25g sodium metabisulfite in 800ml water
2. When dissolved, make up to 1l with water

Second developer

1. Prepare Ilford PQ 1+9 (i.e. 100ml PQ concentrate, 900ml water)

Fixer

1. Use your usual fixer. I recommend Ilford Rapid Fixer 1+4

Most of these chemicals are pretty harmless so long as you don’t eat them. The exception is the concentrated sulfuric acid, which will cause serious burns if it gets on your skin. It is essential to wear nitrile gloves and goggles when handling it. Always add concentrated acid to water, never the other way round. Check in advance what kind of plastic your bottles, measuring cylinders, pipettes and other apparatus is made of, as some plastic will be attacked. Never use metal implements. Glass is fine, but if you store the acid in glass bottles be aware that glass will break if dropped, whereas plastic will probably bounce…

The procedure

1. Kodachrome comes in so many formats. If you have 35mm format, you can load it onto a reel and process in the usual way. I have a 50-foot Super-8 cartridge so I plan to lay the film out loosely in a large photographic tray, usually used for processing prints. It’s not ideal but it’s the best I’ve got. I’ll need to take care to ensure the film doesn’t stick to itself.
2. If you’re removing the rem-jet before processing, do this step now. Otherwise, do it after fixing. Dunk the film in the rem-jet removal bath and agitate it vigorously. The rem-jet should be dissolved but chunks of it will probably come off and start floating around. Try to avoid letting these touch the front of the film, because they will stick. You will probably need several minutes in the rem-jet removal bath.
3. Transfer the film to a container of water. You might like to wipe the film with a sponge or cloth as you transfer it from the rem-jet removal to the water, to remove any bits of rem-jet that weren’t dissolved.
4. Add the film to the first developer for 12 minutes at 20°C
5. Wash the film thoroughly in water
6. Add the film to the bleach bath and agitate continuously. After 30 seconds you should be able to expose the film to room lighting (not daylight). Continue bleaching for about 5 minutes, or as long as it takes to remove the silver image. When all the silver has been removed, the film will be a creamy-yellow colour.
7. Rinse the film in water
8. Add the film to the clearing bath for 2 minutes, with intermittent agitation.
9. Rinse the film in water
10. Remove the film from its reel. Expose both sides of the film to light for the equivalent of 30-60 seconds at 46cm/18″ from a 100-watt tungsten lamp or 30cm/12″ from a fluorescent light tube.
11. Add the film to the second developer for 6 minutes at 20°C
12. Rinse the film in water
13. Add the film to the fixer for 5 minutes, with intermittent agitation.
14. Wash the film thoroughly in water
15. Rinse the film with wetting agent (e.g. Ilfotol), if you like
16. Hang the film to dry
17. For 35mm film, you may wish to cut and mount the transparencies in 2″ mounts for projection. For motion picture film, wind it onto an appropriate spool for projection.

The process at a glance

This table was taken wholesale from Ilford’s document Reversal Processing and is recreated here for convenience.

Processing Steps	Time	Comments
First development	12 min	May be adjusted to give optimum time for particular ISO rating. A longer development time will give a lighter image and a shorter development time will give darker image.
Wash	5 min	Preferably running water
Bleach	5 min	Strong acid and therefore stops development immediately: extend time if necessary for full bleaching: continuous agitation
Rinse	1 min
Clearing bath	2 min	Clearing solution removes any yellow staining caused by bleaching
Rinse	30 sec
Second exposure	1 min per side
Second development	6 min	Development as for normal black & white processing
Rinse	30 sec
Fix	5 min	Fixing as normal for black & white processing
Final wash	10 min	Running water
Dry

The test

I haven’t yet found anything worthwhile to shoot with the Kodachrome in Super-8 format, and it seemed worthwhile to do a test of the reversal processing before risking a rare film. I quickly exposed a roll of expired B&W print film, loaded it onto a reel and followed the above procedure from step 4 onwards.

It was pretty successful for a first attempt. The reversal worked, and I got positive images. However, one of my development timings wasn’t quite right and the transparencies are quite thin. Easily correctable on the computer if I were to scan them in, but they’d be disappointing if projected. I guess either my first development was too long or my second was too short – or perhaps the original camera exposure wasn’t quite right.

This picture shows a segment of the film, still hanging up to dry in the darkroom. The shadows are not dense enough but you can clearly see my neighbour’s car on their drive, in all its positive glory.

Next time I try this, there’s not much I can do to judge the first development as it has to be done in the dark, but I could check the second development periodically to see how dense the shadows are. I’m looking forward to shooting the Kodachrome now!