Speaking of cyanotypes, I just came across an article in an old journal
(1915) reviewing a new process patented by John Lewisohn, of New York.
Briefly:
A negative of a colored object is made on an orthochromatic film with a
yellow filter. From this neg an ordinary blueprint is made. This blueprint
is then colored either wholly or in part with dye or paint, but preferably
by applying eosin for the magenta and aurantia for the yellow, or a mixture
of the two to modify the blue to form any of the spectrum colors. Should it
be desired to make all or any material portion of the print either red or
yellow, or any other color in which blue is not used the blue of the
blueprint is either wholly or partially dissolved by a weak solution of
nitrate of silver, which will fix the colors, and at the same time will
gradually bleach the blue. Further, the blue print may be washed with this
solution if it is desired to merely weaken the blue color of the object,
after the eosin or aurantia has been applied.
Should it be desired to restore the blue locally or entirely, or to darken
the blue color, the blueprint is respectively touched up or bathed with a
solution of ferric chloride, and this may be applied in stronger solution
or in succession until that part of the object is practically black.
Luis Nadeau
NADEAUL@NBNET.NB.CA
Fredericton, New Brunswick, Canada
http://www3.nbnet.nb.ca/nadeaul/