Flattening pastels on parchment

I am looking for recent literature on flattening treatments of pastels
painted on parchment/vellum. The parchment is irregular in thickness,
which seems the cause for the distortions. Any advice is for a
colleague of mine.

Hans-Christoph von Imhoff
Conservator-Restaurer
paintings and painted surfaces
CR-SCR, FIIC, PA-AIC
Chemin des Rochettes 6
1752 Villars-sur-Glane
Switzerland
+41 26 401 07 77
Fax: +41 26 401 08 88

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                  Conservation DistList Instance 11:71
                 Distributed: Friday, February 20, 1998
                       Message Id: cdl-11-71-011
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