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

[etienne garbaux]

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