[alt-photo] Re: The Illusive Black Cyanotype - Any Insight?

[Ryuji Suzuki]

I doubt salicylic acid would tone prussian blue pigment. The iron in the blue 
pigment is tightly bound to cyano ligands and salicylic acid is way too weak to 
undo that.

Salicylic acid was useful in poisoning the redox catalyst activity of free 
ferrous/ferric ions in ascorbate developers, but that was a very different aim. 
Even then, I wouldn't be surprised if there were multiple mechanisms involved 
(e.g., free radical scavenging actions) as I don't think iron-salicylate complex 
is very stable in alkaline solutions.

In the protocol you described, nitric acid is probably used to decompose 
prussian blue to free up iron for further reactions. But you don't want the 
image to become blurry (and lose density) by allowing the iron to freely diffuse 
in the material, so carbonate solution is used in between. But Mike Ware is the 
expert to ask on this topic.

If the objective is to convert prussian blue pigment to brown black, another way 
to do it would be to use a weak solution of sodium sulfide or ammonium sulfide 
(pH around 6).

-- 
Ryuji Suzuki
"Don't play what's there, play what's not there." (Miles Davis)




Gordon Holtslander wrote:
> Ryuji Suzuki uses salicylic acid in some of his developers to sequester iron.
> http://www.digitaltruth.com/data/ds-10.php
>
> I wonder if a salicylic acid could be used to clear iron  in toning cyanotype?
>
> Salicylic acid is a phenolic acid like tannic acid.  It may tone cyanotypes as well.
>
> Gord
>
>
> ----- Original Message -----
> From: Francesco Fragomeni<fdfragomeni at gmail.com>
> Date: Tuesday, September 20, 2011 4:07 pm
> Subject: [alt-photo] Re: The Illusive Black Cyanotype - Any Insight?
> To: The alternative photographic processes mailing list<alt-photo-process-list at lists.altphotolist.org>
>
>> In regard to the gallic acid toning procedure, can anyone
>> confirm what the
>> nitric acid does? My assumption is that it is a clearing agent
>> intended to
>> aggressively neutralize or remove excess iron residue before
>> bleaching in
>> sodium carbonate and then toning in the gallic acid. Can anyone
>> confirmthis?
>>
>> -Francesco



>>>>> On Mon, Sep 19, 2011 at 9:05 PM, Gordon J. Holtslander
>> <gjh at shaw.ca>>>  wrote:
>>>>>> Have you tried this:
>>>>>>
>>>>>> To convert Cyano to black tones:
>>>>>> Place print in solution of 3 drops Nitric Acid added to 1
>> litre water
>>>> for
>>>>>> two minutes transfer to bath of 14g Sodium Carbonate +
>> 160cc water -
>>>> leave
>>>>>> till image disappears and then reappears with an orange
>> tone transfer
>>>> print
>>>>>> to third solution of 14g Gallic Acid + 160cc water - black
>> tones will
>>>> appear
>>>>>> wash 30 min.
>>>>>>
>>>>>> perhaps the ferrogallic process would work;
>>>>>> (from Photographic Facts and Formulas 1940)
>>>>>>
>>>>>> ferric
>> chloride         50g
>>>>>> ferric suplphate
>> (basic)        25g
>>>>>> tartaric
>> acid                   45g
>> water                           500 ml
>>>>>> Dissolve and add
>>>>>>
>>>>>>
>> gelatin                         25g
>> water                           250cc
>>>>>> soak gelatin for 30 minutes and dissolve
>>>>>>
>>>>>> Development details are not given though
>>>>>>
>>>>>> Gord