Re: ferri sesquichlorati

[Katharine Thayer <kthayer@pacifier.com>]

On Oct 18, 2006, at 9:28 AM, Halvor Bjørngård wrote:

> If you have Mike Wares Cyanotype book, have a look on the pellet  
> process. It
> contains gum, ferric and tartaric acid. It is mentioned somewhere  
> in there
> that Prussian blue can harden colloids, but have again not found  
> any closer
> explanations.

If by "Prussian blue" you mean what I mean by Prussian blue, the  
pigment PB 27 (hydrous ferric ferrocyanide, or sometimes  
ferriammonium ferrocyanide) then it definitely doesn't harden gum  
arabic, because I use it for a pigment in the gum process all the  
time; it's become my favorite blue.  Here's a test print made with  
Prussian blue.  It's not a perfect print; there's something weird  
with the coating or the sizing in one corner that flawed the print,  
but you should be able to tell from the rest of the print that  
Prussian blue acts just like any other pigment in the gum process.

http://www.pacifier.com/~kthayer/html/Prussian.html

I'm working on a page about bitmaps where you can see a better  
example, but I'm not finished with that yet.
Katharine Thayer