Tempera and gouache

Iam looking into painting techniques of Ben Shahn from the 1950's.
He combined tempera and gouache in works on paper resulting in some
very problematic flaking. Has anyone analyzed the tempera on his
works on paper or come across this combination from the same period?
I would love to hear from anyone with experience on this type of
work even when it did not display problems or was by another artist.
Thank you,

Daria Keynan
212-645-5245

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                  Conservation DistList Instance 9:55
                Distributed: Wednesday, January 17, 1996
                        Message Id: cdl-9-55-012
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