The Book and Paper Group
The American Institute for Conservation

(Stabilized Humidity Control Package)

by Victoria Blyth-Hill

The following is a brief description of a sealed humidity package, which we call passepartout, used for works of art on paper prior to framing. The package is designed to stabilize the humidity within the framed package and is especially useful for sensitive works of art such as Indian and Persian miniature paintings, Japanese woodblock prints or any work on brittle paper or one with friable or sensitive media. It was designed as a low cost solution for the more sophisticated environmental chambers (used for panel paintings) and to stabilize works of art in transit or in unknown or uncontrolled environments.


Acid-free rag board matt (window matt and backboard) - stabilized to 50% RH
Ultra-violet filtering Plexiglas
Acid-free rag board (2-ply) - stabilized to 50% RH
3-M double-sided encapsulation tape
3-M Scotch 845 Book Tape or any stable trans-parent mylar-type tape (2")
Humidity indicator strip (Source: Multiform Desiccants Inc., Buffalo, N.Y. 14213)
Art-Sorb sheet (Fuji-Davison Chemical Ltd.) or SG 145 Desiccant Paper
(Multiform Dessicants)-stabilized to 50% RH.
2-5 mil Mylar
Acid-free corrigated cardboard (for backing)

Stabilizing RH of Materials:

All of the above materials can be stabilized to any relative humidity, and we generally prefer 50-55% RH. Stabilizing the boards, humidity sheets (Art-Sorb or Desiccant paper), humidity indicator strip and the art work is done by simply keeping them for several days in your controlled working environment and then assembling the art package in this same environment.

Assembling Art Package:

Hinge and matt your art in the normal manner. Attach a sheet of Art-Sorb/Desiccant paper (cut to the appropriate size - corresponding to the matt size) to the 2-ply rag board with double-sided tape. Leave room to attach the humidity indicator strip next to the desiccant paper (the strip has a self-adhesive backing). Cut the mylar to a slightly smaller size than the matt and 2-ply. Clean the plexiglas and place over matted art. Put 2-ply with desiccant sheet and indicator strip behind matt package, with desiccant sheet and indicator strip facing out or away from the art package. Place the mylar sheet behind the package and carefully tape the four borders of the package. Taping can be tricky and requires patience as the whole package is very slippery. I usually place a light weight on top of the plexiglas and slide the package (plexi, matted art, 2-ply and mylar#8211;see diagram) to the edge of a table then tape the sandwich. Be sure that the width of the tape on the surface of the plexiglas does not exceed the rabbet of the frame - as you don't want the tape to show through the frame opening. Now. you should have a completely sealed package!

As a final note, I like to protect the back of the package with acid-free corrugated cardboard, and cut a window into it, in order to see the humidity indicator strip, and monitor the internal humidity of the package

Place the package into the frame provided (note: remember when you order the frame, that the sealing tape will make the package slightly thicker).

This is the basic assembly, but it can be adapted to fit your specific needs. We have had great success with this package and use it frequently for traveling exhibitions. The reason I attach the silica gel material to 2-ply is so that we can recycle the assembly (we generally use standard size frames and matts) and store it for the next package. Note: Prior to attempting a passepartout with an art work, try making a mock-up first.



Victoria Blyth-Hill
Senior Paper Conservator
Los Angeles County Museum of Art

Publication History

Received: Fall 1991

This paper was submitted independently by the author, and was not delivered at the Book and Paper specialty group session of the AIC Annual Meeting. It has not received peer-review