Re: Autochromes
nadeaul@nbnet.nb.ca
Mon, 18 Sep 1995 22:37:21 +0300
>I recall reading about the process. As far as I remember, you divide some
>potato starch grains in three equal amounts, and you dye them red, blue and
>green, such that the grains are still well separated. The dye must be
>water-soluble, but perfectly alcohol-insoluble. You mix the grains
>together, and some carbon powder too, to fill in the gaps between grains.
>The mixture is then mixed in a alcohol-based transparent paint, which is
>coated on some perfectly clean glass. A silver-based emulsion is laid on
>top. Both coats must be very thin, particularly the starch one which should
>be one-grain thick. Exposure takes place throught the glass and thus
>through the grains, to give the colour separation.
>
>I can't recall, but quick reasoning says you should develop, then bleach,
>then expose to white light, then develop again and fix to produce a
>positive. Is this right? Hope this helps- the whole process is supposedly
>quite tricky.
^^^^^^^^^^^^^^^^^^^
The understatement of the year;-) The process is *extremely* tricky, even
if you have access to the original formulas and trade secrets. Several
companies spent millions over decades to match the quality of the
Autochrome and never did succeed...
Most Autochrome lovers have never seen an original. They've only seen
reproductions in books and indeed they can be quite lovely. I suspect that
with a bit of work one could come up with a Photoshop filter that would
approximate the Autochrome effect.
Luis Nadeau VE9LN
NADEAUL@NBNET.NB.CA
Fredericton, New Brunswick, Canada