Hahnemuhle Photo Rag paper

Peter Geraty <pgeraty [at] praxisbindery__com> writes

>Through research I have obtained the following information:
>
>    *   The OBA's are causing this effect
>
>    *   The OBA's alter the reflection of ultraviolet light in such
>        a way as to make the paper appear cooler white
>
>    *   The yellowing occurs in paper which is stacked or contained
>        (apparently it has to do with out-gassing)
>
>    *   exposure to light and air will get rid of the yellowing
>
>What I am looking for is a better understanding of the cause and
>possible treatment.  There is a lot of money tied up in the project
>so reprinting is the least attractive option.  We would like to
>light bleach the pages and then proceed with the binding.  I have
>experimented with a UV light (I don't know if it is UVA or UVB) and
>it has gotten rid of some of the yellowing.  It is very slow and
>possibly I don't have the right UV bulb.  After exposing some of the
>pages to natural light the yellow has dimensioned more evenly and
>perhaps a bit better than with the UV bulb, but the edition is large
>and natural light would be difficult.   I have thought of grow
>lights for plants and sun-tanning lights as possibilities.  We can
>rig up florescent lights and put the right kind of bulb in, if we
>know which one to use.

This is indeed a very curious phenomenon that I have heard about
from a number of printers who print for artists on a large scale.
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.

This being said, I am not sure which mechanisms are at work here and
if the yellowing will reappear later. There is a publication of a
German study that has shown that as the OBAs in inkjet papers are
used up during exposure to light, the papers appear yellower, which
seems to make sense. However, it is stressed that measuring this
loss of blue (it's not really yellowing when you think about it) can
be quite difficult since the OBAs react differently to different
types of light, depending on UV content.

I realize this doesn't really help you with your problem. I would
recommend that you speak to a number of digital printmakers and ask
them if they have had this problem and what they have done to remedy
it. It would be good to get to the bottom of this problem that seems
to be quite common, especially in regards to the Hahnemuhle Photo
Rag paper, since so many artists and photographers are using this
paper. It is interesting to hear that the yellowing is apparently
not a function of the inkjet coating, since you mentioned that you
had used the paper base only.

Martin Juergens
Photograph Conservator
Margaretenstr. 29a
20357 Hamburg, Germany


                                  ***
                  Conservation DistList Instance 21:7
                   Distributed: Monday, May 28, 2007
                        Message Id: cdl-21-7-002
                                  ***