Digital BW, The Print

Clayton Jones wrote:
>
> ...
> While doing some cleaning I found a stack of old work prints from approximately 6 years ago.  Some of them were printed on Museo Silver Rag ...
> There are 5 SR prints, small prints with about 1/2" to 3/4" borders.  They were in the middle of about a 5 inch stack of prints on a variety of matte papers.  All five have yellowed borders.  The yellowing extends inward from all four edges from 1/8 to 1/4 inch and feathers into white (no hard edges), so whatever caused the yellowing appears to have worked its way in from the edges while in the stack. The yellowing appears on both the front and back.  I'm not a smoker and this room is air conditioned most of the time (I'm in South Florida, so even with A/C there is some humidity).  None of the matte prints in the stack had any yellowing.
> ...



Clayton was good enough to send me a couple of samples of the yellowed Museo Silver Rag.  I don't have the chemistry background or tools to know what caused it, but here are my observations:


The spectro measures the outside 1/4 inch of the front paper margin as
having a Lab B of from about 4.5 to 5.1.  The inside of the 3/4" paper
margin, closest to the image and furthest away from the edge of the
paper, has a Lab B of 2.1 to 2.4.  The back side of the paper shows a
similar pattern, although the Lab B values range from 3.3 at the edge
to 1.2 in the interior.  So the effect is on both surfaces, but worst
on the front.

The yellowing looks a lot like what I saw on the backs of some stored
silver prints (fiber paper), that, I believe had been attacked by
airborne acids, possibly put out by other paper in the metal cabinet.

I used my pH test pen on the samples and found that the surfaces of
the Museo were probably somewhat acidic -- definitely not buffered.
The interior paper of the Museo did appear to still have a good amount
of buffering in it.  The surfaces of the matte papers were well
buffered.  I then tested the surfaces of newer Museo I had.  These
newer ones did appear to be buffered or otherwise tested as having a
surface with a relatively high pH.

All of this does not prove that we're dealing with acid attack, but it
is consistent with that hypothesis.

I'm not sure what would be on the surfaces of the paper that would
yellow.  We usually think of the yellowing being of the paper
cellulose fibers being attacked by acids.  With these glossy "papers,"
the paper is actually in the interior and separated from the surfaces,
usually by polyethylene. In the case of the Museo, the interior paper
appeared to be well buffered and quite different than the surfaces.

It appears polyethylene can also yellow.  It looks like inappropriate
materials combined with oxides of nitrogen in the air are
possibilities.  See
http://www.tencate.com/8776/TenCate/TenCate-Grass/Region-EMEA/English/en-Grass/Products-amp-Services/Product-advisory/Gas-fading

I suspect these more "advanced" "baryta" glossy papers are still a
form of RC paper.  Something is certainly separating the well-buffered
interior paper from the front and back surfaces, and I'd guess it is
the usual polyethylene or a close relative of it. 

Again, I can't say what caused the yellowing, but it is clearly there, and its pattern suggests an airborne chemical played a part in the process.

Paul
www.PaulRoark.com