Hahnemuhle Photo Rag paper

Peter Geraty <pgeraty [at] praxisbindery__com> writes

>I am involved with a publisher who has printed a job on uncoated
>Hahnemuhle Photo Rag paper.  The paper contains Optical Brightening
>Agents (OBA).  It is the base paper which may later be coated to
>enable digital printing.  In this case the paper is uncoated and has
>been printed on a letterpress using a rubber based ink.  During the
>sewing of the books, we have noticed a yellowing effect occurring. I
>have seen the same effect on digital papers before, but they were
>coated papers.  On the Hahnemuhle paper, the yellowing is a pale
>acid-yellow.  On the coated digital papers I have seen, the
>yellowing has been the same acid-yellow but much stronger.

and Martin Juergens <post [at] martinjuergens__net> writes

>Every now and then a print or a batch of prints will yellow when
>kept in drawers or in folders, in any case when *not* exposed to a
>source of light. By simply leaving the prints out on a table top for
>a few days the yellowing disappears.

>Every now and then a print or a batch of prints will yellow when
>kept in drawers or in folders, in any case when *not* exposed to a
>source of light. By simply leaving the prints out on a table top for
>a few days the yellowing disappears.

I don't know if this is germane (I missed the beginning of this
string) but here's a different approach regarding the cause of the
yellowing.

I read once about the search for the agents responsible for
yellowing white tee shirts kept in storage. The investigation took
years--the culprit was finally found to be BHT from the plastic bags
used to protect the garments. (The BHT was used as an anti oxidant
in the otherwise benign polyethylene bags.) The BHT molecules
apparently migrated from the bags to the fabric, and then were
"broken" into short sections by airborne pollutants.

What brought this story to mind was the "fix". Garments were merely
exposed to bright light; the BHT chains became transparent again,
and the yellow patches disappeared. Could some similar method be at
work here?

Jerry Shiner
Microclimate Technologies International / Keepsafe Systems


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                  Conservation DistList Instance 21:9
                   Distributed: Friday, June 8, 2007
                        Message Id: cdl-21-9-009
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