[alt-photo] Re: Don't take the brown FAC!

[Peter Friedrichsen]

Trevor,

As far as altering it to change it to the green variety, I had no 
success with this by adding additional ammonia and citric acid. It 
appears that above and beyond the ratios of iron, ammonia, and 
citrate, the way in which it is made also affects its final 
properties. I know this because I make my own green variety from scratch.

Essentially it is made by adding ammonia (or use ammonium 
bicarbonate) and citric acid to iron hydroxide ( a messy red mud)  If 
you add the citric acid first,  to make ferric citrate, then add 
ammonium citrate to make FAC, it will make the brown variety. Now, if 
you add ammonium citrate + citric acid, both together to this mud, 
then the green variety forms. So it seems that as the ferric 
hydroxide dissolves, it must have the ammonia component available, or 
else you will just get the brown variety, and it will stay brown even 
if you attempt to re-balance the ratios.

At least this is my experience.

Peter Friedrichsen



At 09:49 AM 05/04/2010, you wrote:
>Hey gang,
>
>Well, after a long wait, I finally have chemistry for gum and 
>cyanotype...or so I think. I opened my FAC and discovered that it 
>looked VERY brown. After mixing according to the traditional 
>cyanotype in alternativephotography.com, it doesn't have that 
>iridescence I remember, and the dried emulsion is brown. I haven't 
>exposed one yet because my sun decided to hide for the rest of the 
>day's useful light. In the Unblinking Eye, there's mention that the 
>brown FAC is less sensitive and has a lower tonal range than the 
>green. Should I be making an effort to reduce contrast? Any 
>suggestions as to how I might alter the solutions to compensate? 
>Something tells me I'm going to have to really dial in a specific 
>curve for this ride.
>
>Trevor
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