Re: treating paper with oxalic acid

[Judy Seigel <jseigel@panix.com>]

On Tue, 21 Aug 2001, shannon stoney wrote:

> Speaking of Dmax:  I just read an article in View Camera (I read it in the
> store and didn't buy it so I can't say who the author was) about treating
> Rives BFK with oxalic acid to make it more amenable to pt/pd printing, so
> that the blacks would be blacker and the scale in general longer.  (The
> author then prints over the pt/pd print with gum, I think.)  I wonder if
> this would work for other processes also, like cyanotype and vandyke?  I
> think Judy wrote in Post Factory that she didn't like Rives BFK for
> cyanotype, but I wonder if treating it with acid this way would solve
> whatever problems it has. It certainly is a beautiful paper in other
> respects.

In Post-Factory #5 (printed August 2000) on bottom of page 35 I show 4
21-steps, given precoats respectively of nothing, glacial acetic acid,
aluminum potassium sulfate, and 1% oxalic acid. The increase in tone and
D-max was appreciable, especially the oxalic acid. No doubt other acids
would also do something.

I didn't write an entire article about this -- I leave that to the
glossies (Post-Factory can't spare the space !!!). What made me think of
it was observing that the cyanotype formula that has the oxalic acid in it
did show greater density when it was fresh, tho the effect wore off in a
week or less after mixing, whereupon formula lost its "edge," & began to
stain highlights.  I figured that just putting the acid on the paper might
work without the long-term trouble... and it did. Other acids might also
be worth trying.

However, I did not compare the effect of the acid precoat to simple double
coating, and/or an acid bath as first wash, which is said to intensify
cyanotype. I wonder if the article about the coating for pt/pd did that?

Judy

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