I am doing some research for a book and I wondered if anybody knew the approximate processing times for autochrome plates? Specifically during the Edwardian Era (although I wouldn't expect anyone to know first hand!). I can find a lot of information about the process, just very little about the time taken and whether it would have been a matter of minutes or hours.
It would be similar to other glass plates processing time. Processed thing is a panchromatic BW Emulsion and not takes more than few minutes and after all with fixer in few minutes.
One book, off the top of my head, that has complete information regarding the processing of Autochromes is EJ Wall's "History of Three-Color Photography". It should give you a number of processing instructions.
It's a reversal process, but it won't be exceptionally long. 30 minutes maybe?
I have got no Autochrome process shedule at hand, but all films with combined screens (including Lumiere Filmcolor) take about 30min+drying for processing.
There is no hint whatsoever that in "Edwardian Times" processing was significantly different.
Ok I have an antique lab manual for processing autochromes from 1920. This is an overview of the instructions.
A test batch of first developer is as follows
Metol 1 gram
Sodium Sulphite dry 50grams
Sodium Carbonate dry 35grams
Potasium Bromide 5 grams
Potassium Thiocynate 9 grams
Water to make 1000cc
the developer temperature times are as follows
65F - 5 minutes
72F - 4 minutes
75F - 3 minutes
In small tank development agitation should be 5 seconds ever 30 seconds.
Wash film in running water for 2 minutes. (water MUST be tempered to match the developer temperature)
water to make 1000cc
Potasium Bichromate 5grams
Sulphuric Acid 98% 10cc
(Mix above chemicals slowly in order given)
Bleach time is 4minutes tempered to the same as previous baths.
NOTE:bleaching must be done with constant agitation and after the first 2 minutes the following two can be done in white light by inspection.
After Bleaching the plates image should be clearly visible with no traces of black silver left and the emulsion should have a creamy white appearance.
Wash in running water for 4 minutes. tempered to same as previous baths
Sodium Hydrosulphite 10grams
Sodium Bisulphite 14 grams
water to make 1000cc
The time for this bath is 1 minute.
FIX USING HARDNER
STEP 7 wash for 15 minutes.
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So anyway if u have autochrome and they were somehow magically preserved in mint useable condition thats the forumla for making small volumes of chemistry
for autochrome lab test conditions. The formula autochrome accredited processing labs of the day used was identical the amounts were just increased.
Hope that helps.
Thanks for posting that Stephen; I find it really interesting that they use a sodium hydrosulphite reversal/fog. Wouldn't that give a sepia toned image, or am I thinking of sodium sulfide...?
Sodium hydrosulfite, more correctly termed sodium dithionite CAS 7775-14-6, produces a black silver image. I once tried it for making prints. It works but smells really bad. However the color of the silver image in an autichrome slide is immaterial since its purpose is only to block light from certain colored starch grains.
That's interesting that it uses a fogging reversal bath rather than a second developer.
Thanks for the clarification Gerald. If it were to form a brown image however, that could introduce some weirdness since technically the silver wouldn't be acting as a neutral filter anymore; it'd be letting in a bit too much yellow/red.
Yeah, quite curious about the fogging bath, but makes sense I guess from a quick processing standpoint.