Autochromes...

[glbeas]

One article I'd read on the process a long time ago gave me the impression that the color filter matrix was on a sheet of glass in front of the film and was not put through the developers with the film or glass plate with the image on it. It was then reregistered after the image was processed and dried. Potential problems are dimensional stability of the film, which tends to change size a bit with humidity levels.A glass plate would work best with such a process with an Estar base film second.

[glbeas]

Another thought, if the color filter matrix was printed on the base side of a film without antihalation and exposed through the base you would eliminate the problem of trapping the emulsion under a waterproof layer of pigment. There would still be problems from dimensional distortions from the angle of view from the lens to the film but with LF I think it would be minimised. If you were using a panchromatic liquid emulsion you could coat over the matrix and expose through the base with none of the distortions.

[jd callow]

My reading on the process is this.

1. The glass plate is coated with dyed potato starch (one listing had it as rgb the other orange, green violet)
2. this layer is varnished
3. On top of this is a layer of panchromatic emulsion
4. the film is exposed through the glass
5. the developed plate is viewed through a second plate that has a matching dyed potato starch layer

The fact that they required the addition of the second plate to view limited their public exposure. The advent of digital technology (the ability to scan and digitally filter the image without the viewing plate) has brought them back into the public eye.

I read this on the web take it for what it is worth.

[Ole]

I think you're wrong about step 5 - the starch grains were completely random and impossible to reproduce. You got one original, and that was that. Rather like slide film, in fact....

[Photo Engineer]

Ole is correct, there is no step 5.

1. Coat dyed starch grains + coal dust in a varnish and / or honey mixture and harden. This was on a glass plate.

2. Coat a panchromatic emulsion over this - losing a huge amount of speed.

3. Expose through the glass plate.

4. Reversal process in a normal B&W process.

5. View.

This complete process is described in detail in "History of Color Photography" by Friedman. It includes optimum grain size based on expected magnification and also describes Dufay and other similar processes.

Step 5 could be used in some lenticular processes where the lenticules were reproducible and could therefore be interchanged. It did take manipulation of the lenticular 'mask' in order to register the color separations properly, and so there was some adjustment necessary for each image if this method was used. It was not very popular, and integral lenticular screens were the main choice.

PE

[jd callow]

Very possible Ole. I have never seen one first hand and most of the sites I have viewed I have had to translated.

My item 5 and the digital step may be furthering a mis conception started by another or (less likely) a mis reading of a translation.

I have also read that the process started in 1907 and 1904 and ran until 1933 or 1937.

One translation was rather neat in that it stated the brothers 'light' invented the process and film.

[htmlguru4242]

Let's shift the focus here back to actually making the slides with current technology...

1. Coat dyed starch grains + coal dust in a varnish and / or honey mixture and harden. This was on a glass plate.

2. Coat a panchromatic emulsion over this - losing a huge amount of speed.

3. Expose through the glass plate.

4. Reversal process in a normal B&W process.

5. View.

Is definetely the correct process. There were a few steps in between those (such as one that flattened the startch grains), but that would be unecessary for testing purposes. Also, I believe that the original plates were slighty concave, allowing for easier coating of both emulsion and filter screen.

I'll work in printing onto film and making a screen. However, the question still exists as to what you can use for water insoluable dyes / pigments. I'm still in need of ideas...

[jd callow]

Why not shoot through the film as the original was shot through the plate? This way, I would imagine, you would have any number of ways to seal the colour and filter layer.

[htmlguru4242]

hmmm .... that is a good idea- a coating could easily be made on hte base of the film. hte only problem would be removing hte anti-halation backing that is present on almost all modern films. I do not know of any (with the exception of Kodak HIE, which isn't suited for this) that would work.

Does anyone know of films with no anti-halo coating and a relatively clear base, or of any way of removing the anti - halo base from films that have it before exposure?

[Photo Engineer]

I would suggest any good sulfonated azo dye for starters. There are some still used for Dye Transfers and their names are posted on the SIG web site for Dye Transfer enthusiasts. Some good food dyes might work if they are suitably immobilized by a mordant.

You may need a quaternary ammonium salt to function as a mordant on the starch, to hold the dyes in place in case they tend to wander. It depends on how mobile they are during coating and processing. That will have to be experimented with.

If you have a removable screen, you have the very difficult task of re-registration after processing, mentioned above, and which will cause color fringing and halos at best, and no suitable color image at worst.

Most films have antihalation that is removed only by processing or wetting which will ruin the film for this application.

That does not mean that this cannot be done, merely that a lot of searching for the correct materials will have to be done before a start can be made.

Remember that the number of grains and their size are determined by the size of the original transparency.

PE