From: Peter Marshall (petermarshall@cix.co.uk)
Date: 07/31/02-03:27:00 AM Z
> Hello,
>
> Pigment photographs use the action of light on diChromates (Cr2O4) to
> make colloids (albumina, gum...) insoluble, thus retaining the pigment
> in the picture.
>
> The problem is that diChromates are very toxic.
>
> The periodic elements table shows that Molybdenum (Mo) and Tungsten (W)
> are on the same column than Chromium (Cr). The big advantage is that
> these products are not toxic compared to Cr.
>
> Did anyone heard about the use of (di)Molybdates or (di)Tungstates
> instead of diChromates on pigment photographies ?
>
> If yes, what is the recipie ? Apparently, these Mo/W-ates are
> photosensitives to UV but may not be sensitive enough to natural light
> to take pictures... any information ?
>
> Is there an easy process to take photographs without the use of toxic
> products. This process should be handled by children from A to Z using
> a hand made pin hole camera (even is exposure is taking hours). That is
> why toxic products are definitely not allowed.
>
> Best regards
>
> Frederic
>
> _________________________________________________________________
> Discutez en ligne avec vos amis ! http://messenger.msn.fr
>
>
Cyanotype has traditionally been used for this purpose, although it is
very slow. The traditional process uses ferric ammonium citrate, potassium
ferricyanide and water.
Potassium ferricyanide is not absolutely harmless, but a LD50 of 2970 mg
kg-1 (on mice) suggests it relatively safe, and it is probably largely
excreted rapidly and unchanged if ingested. There is quite a lot of detail
on it in:
http://ntp-server.niehs.nih.gov/htdocs/Chem_Background/ExSumPdf/PotassiumF
erriCyanide.pdf
(join the two lines of the address)
the evidence seems to suggest it is relatively harmless.
Similarly ferric ammonium citrate has an LD50 of 1000mg kg-1 for mice and
is generally regarded as safe. I think it has been used as a food additive
and in iron tablets.
You will find MSDS on both on the web. The dangers of water are too well
known for me to need to write more.
Peter Marshall
Photography Guide at About http://photography.about.com/
email: photography.guide@about.com
_________________________________________________________________
My London Diary http://mylondondiary.co.uk/
London's Industrial Heritage: http://petermarshallphotos.co.uk/
The Buildings of London etc: http://londonphotographs.co.uk/
and elsewhere......
This archive was generated by hypermail 2.1.5 : 09/19/02-11:11:01 AM Z CST