[alt-photo] Re: Alternative Exposure Unit (no pun intended)

[Peter Friderichsen]

Keep in mind that this unit as pictured uses spiral compact 
fluorescent lamps. These will not work nearly as well if your 
chemistry uses light sensitive iron salts rather than the 
dichromates. The dichromates are light sensitive over a wider range 
of the spectrum. They can be exposed with blue light and are still 
somewhat senstive to green. The iron salts such as ferric ammonium 
citrate (oxalate) have most sensitivity in the UVA regoin

I did an experiment that confirmed this. I cut up some  blue, green, 
yellow, and red lighting gels into squares and mounted them on a 
transparent sheet, then I shone a slide projector at very close range 
through the strip and onto a test strip of dichromate/gum, and a 
second strip of ferric ammonium citrate/potassium 
ferricyanide(cyanotype). The dichromate exposed considerably in blue 
moderately in green and slightly in yellow none in red. The cyanoype 
showed only a mild exposure under the blue square.

Peter Friedrichsen

At 04:58 PM 03/11/2010, you wrote:
>Christine, Group:
>
>I had been using a custom made BLB set up with 8-24" bulbs for over 15
>years. The bulbs are very expensive to replace and my exposures were 90
>seconds to 7 minutes. Last month Barry Schmetter brought in a Fotodiox unit
>for me to use for a gumprint demo at the Large Format and Alternative
>Photography Gathering (Metro Wash DC). Using my gum/pigment mix 1:1 with 15%
>ammonium dichromate sensitizer I was able to reduce my first emulsion from 7
>minutes to 70 seconds. It was perfect. The second emulsion was correct in 30
>seconds. This unit has completely changed the way I print.
>
>  http://www.fotodiox.com/catalog/product_info.php?products_id=78 fitted it
>with 16 Bright Effects (swirly type; 26 watts daylight or 6000K from Lowes).
>The unit is intended to sit on a lighting tripod but I added a clamp and
>attach it to a heavily loaded bookcase. The unit is currently going for $135
>+ shipping. Add $30 for a clamp if you can't rig up something, a builder
>pack of the bulbs, and you have a very fast, compact, and portable exposure
>device.
>
>Best,
>Carole
>
>
>
>On Thu, Mar 11, 2010 at 4:18 PM, Christina Anderson <zphoto at montana.net>wrote:
>
> > Has anyone bought one of these and used for alt or gum?
> > And what is the best URL for a plan to build one's own?  Apparently the
> > plan I hand out to students out of Nadeau's is incomplete, but since I am a
> > building failure, I can't explain why it is incomplete.  I wouldn't know a
> > magnetic ballast from a martini frankly.
> > Chris
> >
> >
> > http://www.silkscreeningsupplies.com/site/799934/product/RXP2024
> >
> > Christina Z. Anderson
> > christinaZanderson.com
> >
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