[alt-photo] Re: red spots in pt/pd

[Christina Anderson]

Thanks, Etienne! 
Chris

Christina Z. Anderson
christinaZanderson.com

On Jan 21, 2012, at 2:33 PM, etienne garbaux wrote:

> Keith wrote:
> 
>> Black spots. Red spots. Pink Pt/PD seemed to be the trouble at the time.
> 
> Both black and red spots are most often (IME) caused by tiny flakes of metal embedded in the paper from calendering rollers or other paper-handling machinery (or steel wool used to clean machinery) at the time of manufacture.  These metal bits are the main reason I soak papers for 10-15 minutes in ~3.5% HCL (then wash very, very well) before coating.  There were some papers 10-15 years ago that were horrible in this regard, and many comments on-list.  At the time I was able to use the same papers, with the HCl bath, with no problems.
> 
> Pink (not spots -- overall, or in patches) is generally (IME) a result of failed clearing.
> 
> As I said on another thread (re: clearing), but even more so with respect to actual metal bits, you need a mineral acid to dissolve the metal -- organic acids will not do (although Phosphoric acid sometimes turns them directly black/brown, not really much help...).
> 
> Best regards,
> 
> etienne
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