By Rebecca Johnson, Preservation Technician
After years of lugging mail by train, by automobile, and over the shoulders of postal workers, more than one hundred and twenty five bags in the museum’s collection are receiving much-deserved attention in the preservation department. To give museum visitors a peek behind the scenes, we recently brought a dozen of the most interesting mailbags onto the museum floor and shared the preservation techniques necessary to make sure these fascinating bags, pouches, sacks, and portmanteaus last forever.
Rebecca Johnson explaining preservation techniques to museum visitors.
One of the things I enjoy most about my job is working with different mediums; whether it’s leather, cloth, plastics, ceramics, stone, metals, etc. Of course, I have some materials that I like more than others, but the variance is enjoyable. The collection that allows me to work with the widest array of materials is the mailbag collection. When I was deciding what mailbags to select for viewing by the public, I focused on the three most challenging materials: leather, canvas, and plastic. I wanted to show the public how much thought goes into caring for each specific material based almost solely on its composition.
A leather mailbag in the museum's collection.
In the preservation department we use many varied materials to provide long term care for the museum’s collection. The materials I used in the mailbag project were: corrugated board, unbuffered tissue, buffered tissue, PVA (poly vinyl acetate) glue, twill tape, charcoal lined paper and labels. We use whatever material is most appropriate for the object composition and needs. So now, let’s focus on the three materials I mentioned above.
Leather is one of the most complex materials we work with. The first step to re-housing leather is to build a custom box out of blueboard adhered together with PVA glue and twill tape. The blueboard is a buffered material that has an alkaline “buffer” that prevents other acids and harmful materials from entering or exiting the box, providing a layer of protection for the leather object. Then we add a thin layer of charcoal liner on the inside of the box. The charcoal constantly cleans the air in the box keeping pollutants away from the object. Finally, since leather is protein based it responds badly to the alkaline buffer in the blue board, we place a layer of unbuffered tissue paper between the object and the box.
Canvas is a much easier material to work with. Being cellulose based, unlike the leather which is protein based, it has no harmful reaction to buffered material. Since canvas is meant to be a pliable material, we often do not build custom boxes. We place them in clean drawers layered with buffered tissue paper. As long as they are kept unfolded in a cool, dry environment, they are easy to maintain.
Plastic is a relatively new material. Having only become common in the 1950s the museum preservation and conservation professionals are still waiting to see what is the best long term method to care for plastic. However, we do know that heat rapidly speeds up degradation so we are careful to keep the plastic bags in a cool, dry environment. Since most plastics are either petroleum or starch based we separate the plastic bags with buffered tissue. Sometime plastic becomes very brittle and in that case we have to build them their own custom trays or boxes.
NPM Collections Department members, Rebecca Johnson, Patricia Raynor and Caitlin Badowski.
These are the basics of what we have to consider when preserving the objects in our collection, and the protocol changes based on what we are working with. I hope that I was able to give you some insight into the world of museum preservation. After working behind the scenes so much it’s great to bring this to the public’s attention.
If you have any questions or would like more information, check out the preservation page on our website or contact the preservation department at NPMPreservation@si.edu.