[Alt-photo] ferrous vs. ferric

Christina Z. Anderson christinazanderson at gmail.com
Tue Mar 22 14:23:40 UTC 2016


Thanks, Diana and Gilles,
Ahhh, Gilles, this is good. I can understand bright green and amber yellow.
For some odd reason I have never mixed the ferric from powder, yet, I have always used my own palladium mixed from powder. Now, from what you say below, it’s a no-brainer.
I’m now a convert.
How easy to store bulk powder and never have to worry about running out (for me but even moreso for my students I can keep a supply on hand and not worry about it going bad).
Chris
PS I love the “story” which always puts a name in context.

On Mar 22, 2016, at 8:17 AM, Gilles Lorin <gilles at gilleslorin.com> wrote:

> Hello again Christina, 
> 
> This is another hot topic for me right now! 
> 
> To make a long story short, I just moved to Germany from the U.S. In the U.S. I would always buy my ferric from B&S in solution. Arrived in Germany 6 months ago, there is no ferric in solution available anywhere in Europe. The only source is in France but it has to be prepared over 5 days with oxalic acid and hydrogen peroxide. Judging from the kryptonite green, it’s very rich in acid oxalic, which I read is not the best solution. Nonetheless, I’ve been making some very nice prints with it. But keeping consistency from one batch to another has been challenging. Which means that overtime I prepare a new batch, I have to redefine the density range and linearize. 
> 
> Last month, I ordered some powdered ferric from B&S, and it has simplified my life. It’s very easy to mix: heat water at 180F, put 25g of powder for 100ml of water; mix for 30 seconds and let dissolved. It’s very easy and night and day. The color is more an amber yellow, which indicates a low content in oxalic acid. 
> 
> As far as the shelf like of the powder is concerned, Melody Bostick said years. 
> 
> Sorry for the story, but i thought it would respond in part to your question. 
> 
> Best wishes, 
> 
> Gilles 
> 
> Gilles Lorin
> Atelier Gilles Lorin
> Moltkestrasse 8b
> 79379 Müllheim-Baden
> Germany
> 
> m. +49 160 127 3448
> e. gilles at gilleslorin.com
> 
> www.gilleslorin.com
> 
> 
> 
> 
> 
> 
> 
> 
> On Mar 22, 2016, at 2:55 PM, Christina Z. Anderson via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org> wrote:
> 
> Chemistry question here:
> 
> I apologize that I did not follow the discussion of the last several months about hard-to-dissolve ferric oxalate because I always buy mine ready-mixed from Bostick following a discussion years ago about this very issue. I’ve never used it dry. Their solution lasts a couple years and if I buy a large quantity I store it in the fridge and it has never gone bad on me.
> 
> I am wondering though whether buying it in the powder form is a) a good idea and b) has a longer shelf life?
> 
> Am I correct in assuming ferric can change to ferrous with age?
> 
> And that ferrous is harder to dissolve than ferric?
> 
> And that if your “ferric oxalate” powder is hard to dissolve/never dissolves that means it  has changed to the ferrous form?
> 
> I guess I am just trying to ascertain whether there is any benefit to buying and storing the powder and how long the shelf life is. I assume people mostly do this for the cost savings if they are uber-platinum printers doing it on a daily basis (like I buy gum by the gallon).
> 
> Chris
> 
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