Conservation of pith paper

In response to Ingelise Nielsen's inquiry, treatment was completed
recently in the PMA paper lab of an album containing nine watercolor
paintings on "pith paper".  The paintings were adhered at the corners to
album pages made of flexible, poor quality paper.  Blue ribbon was
placed to overlap the pith edges, and adhered at the corners as a
decorative border.  Due to handling and flexing, the brittle pith sheets
were fractured and had many losses.

We removed the ribbons and pith sheets from the album pages
mechanically, with local moisture applications.  When slightly
moistened, the pith became tacky and butt joins could be made almost
invisibly by brushing dilute methyl cellulose on each side and drying
between soft blotters with light weight. Joins that no longer met were
bridged on the verso with lightweight Japanese tissue, also adhered with
methyl cellulose.  Moisture was kept to a minimum, to prevent
over-softening of the pith, which expanded readily and was easily
deformed.  We did not attempt to find new pith paper.  A few losses in
colored areas were filled with inserts made by laminating sheets of
Japanese tissue.

The inserts were toned with dry pigments bound with methyl cellulose,
cut to the exact size of the loss, and bridged on the verso as stated
above.  Losses outside the design areas were not filled, but would be
difficult to compensate successfully with anything other than pith
inserts.

After treatment, the paintings were rehoused in sink mats, with the blue
ribbon adhered to the top (window) mat to hold the painting in place.
The paintings were not adhered in any way. The sink mats were cut to the
same size as the original album, thus maintaining the original
presentation as much as possible.  The nine paintings are now in
separate sink mats with folder covers and are stored in a box with the
empty album, for study purposes.  Each painting can now be handled
easily and can be exhibited separately or as a group.

Approaches to the treatment of "pith paper" are also discussed by
members of the AIC Book & Paper Group in chapter four of the Paper
Conservation Catalog (Support Problems, page 102).

Julie Ream
Getty/NEA Fellow in Paper Conservation
Philadelphia Museum of Art
PO Box 7646
Philadelphia, PA 19101-7646
Fax: 215-236-4465

                                  ***
                  Conservation DistList Instance 8:67
                Distributed: Thursday, February 23, 1995
                        Message Id: cdl-8-67-003
                                  ***