The Postmaster General’s Collection: Case Studies in Conservation Treatment

By Scott W. Devine, Museum Conservator

The National Postal Museum is responsible for the preservation of over 6,000 works of art that are on loan from the United States Postal Service, Postmaster General’s Collection. The art represents a broad range of mixed media works used to create United States postage stamps from the 1950s to the present day. Objects from the Postmaster General’s Collection are frequently requested for loan and exhibition and are often included as an integral component of philatelic exhibitions at the National Postal Museum. The fragility of the artwork and its ongoing use in exhibition and research make long term preservation of the collection a high priority for the museum.

The museum recently processed 90 original works of art on paper, oil paintings, and three-dimensional objects from the Postmaster General’s Collection. The processing of new objects involves coordinating an annual transfer from the United States Postal Service, reviewing each object to assess its conservation needs, and creating a detailed object record in the museum’s database. The new object record includes an image and a description of the object, including its dimensions and material components (e.g., pastel on paper, oil on canvas, etc.). Understanding the material components of the object is essential in order to evaluate its condition and select the proper housing, which may include simple acid free paper folders or more specialized custom-designed storage boxes. Basic stabilization and rehousing of each object are completed during the initial stages of processing while more complex conservation treatments are scheduled to be completed before the next annual transfer. Stabilizing and repairing objects as they are received guarantees that the collection will be available for exhibition and research when needed.

This post outlines the steps taken to preserve original art used to create three iconic stamp series issued in 2012. Each stamp series was designed by a different artist and represents its own unique preservation challenges regarding materials and techniques. Viewed as a collection of case studies, these artworks offer compelling insights into best practices for repairing and stabilizing modern works of art on paper.

Great Film Directors Forever Stamp Series

The Great Film Directors Forever Stamp Series honors four filmmakers: Frank Capra, John Ford, John Huston, and Billy Wilder. The stamp art combines a portrait of each man with a scene from one of his most iconic works. The art was created by award winning artist Gary Kelly using unfixed pastel on heavy cotton paper. The unfixed pastel is heavily applied, resulting in remarkable depth and texture. In each artwork, the paper support had been taped to a rigid backing board. The masking tape used to attach the paper had become yellow and was beginning to discolor the original paper support.

Masking tape, which can result in permanent stains and embrittlement of paper if left in place too long, was removed from the surface of the artwork using a combination of heat and low-level mechanical pressure to avoid tearing the paper. A Zephytronics® air pencil was used to provide controlled heat, just enough to soften the masking tape adhesive without melting the tape carrier or scorching the paper substrate. Using heat for tape removal is a slow process that requires careful testing and constant monitoring. The last remnants of the sticky adhesive residue were removed using a crepe eraser.

Once conservation treatment was completed, the artwork was re-mounted onto acid free matboard with non-adhesive corner mounts and placed in custom designed boxes which allow for easy display and secure long-term storage. Minimizing movement and vibration of unfixed pastel is essential for long term preservation of these fragile objects: spacers inside the new box ensure that the artwork will not shift when the box is closed.

A total of six unfixed pastels were treated as a part of the project. Once treatment was completed and the objects were photographed, the art will be housed in a climate-controlled vault at the National Postal Museum until it is needed for research or exhibition.

Innovative Choreographers Forever Stamp Series

The Innovative Choreographers Forever Stamp Series pays tribute to four legendary choreographers: Isadora Duncan, Katherine Dunham, Bob Fosse, and José Limón. Designed to look like posters advertising a performance, the stamps capture the nuances of each performer’s individual style. Art director Ethel Kessler designed the stamps with illustrations by James McMullan, widely known for his work for Lincoln Center Theater in New York City. McMullan’s use of vibrant watercolor paint is exceptional and gives each work an intense energy. The watercolor paper is taped to a backing board with, in some cases, multiple layers of tape which must be removed using a range of techniques.

The Postmaster General’s Collection is particularly useful for research as it sometimes includes multiple versions of a stamp, including designs not chosen for the final stamp. One of the watercolors not chosen for the Isadora Duncan stamp was in the best condition, with only one layer of white pressure sensitive tape holding the watercolor paper to the backing board. Preliminary testing revealed that the white tape could be removed mechanically without the use of heat or solvents.

Removal of the white tape represents a successful preventive treatment. Once removed, it was clear that the acidic adhesive had already begun to yellow and deteriorate after less than ten years. Leaving the tape in place for a few more years would have led to acid migration from the tape to the watercolor paper substrate, discoloring the paper and leaving stains that would have been significantly more difficult to remove.

The artwork selected for the Isadora Duncan stamp was in overall good condition and included a plastic overlay containing the graphic design elements of the final stamp. Removing the plastic overlay, which was attached with clear pressure sensitive tape, allowed for closer inspection of the watercolor. Two layers of tape were used to secure the watercolor to the backing board: white pressure sensitive tape and remnants of a brown tape applied with a water-soluble adhesive which would have to be removed with moisture rather than heat.

Unlike pressure sensitive tapes which use acrylic or other thermoplastic adhesives which can be removed with heat, many older tapes use water soluble adhesives such as animal hide skin glue or starch pastes. These adhesives are removed with the application of moisture or, in more difficult cases, the use of enzymatic solutions. In this case, removal of the brown tape adhesive was accomplished with a thin poultice of methyl cellulose, a common conservation adhesive and traditional poultice. When placed directly on top of the area being treated, the moisture from a relatively thick 5% solution of methyl cellulose in deionized water slowly permeates the tape adhesive, allowing it to be carefully scraped away.

Several watercolors in the Innovative Choreographers series were adhered with heavy brown tape on all sides, including various versions of stamp art featuring Katherine Dunham, Bob Fosse, and José Limón. The José Limón stamp art was the most challenging in terms of the amount of tape: heavy brown tape on three sides which would make it difficult to remove the adhesive with a traditional poultice without over humidifying and potentially cockling the paper substrate.

To provide a slow and controlled introduction of moisture, gellan gum was chosen as the delivery method rather than methyl cellulose. Gellan gum is a water-soluble polysaccharide produced by the bacterium Sphingomonas elodea which was discovered and isolated in 1978 from lily plant tissue. Gellan gum was initially identified as a substitute gelling agent for agar and is widely used in the food industry. Conservators have been using gellan gum for over a decade as a delivery mechanism for deionized water as well as a range of organic solvents used to reduce stains on paper. Gellan gum poultices are prepared according to specific recipes based on the quantity needed at the time.

Gellan gum is cooked and poured into a tray for cooling. The size of the tray determines the thickness of the gum: in this case, a 1cm thick sheet of gellan gum was formed and cut into strips that matched the size of the brown tape. Placing the gum on top of the tape and waiting for 30-40 minutes allowed moisture to slowly transfer through the tape to the tape adhesive. Once the adhesive was softened, the tape could be lifted away easily.

Residual traces of adhesive were removed with a microspatula, and the object was placed under light weights for three weeks to dry and to ensure that the watercolor paper remained flat. Drying under tension is critical in maintaining planarity and ensuring that the paper substrate does not cockle or stress the watercolor media. Once completely dry, the artwork and the plastic overlay were housed in separate acid free paper sleeves in an acid free folder in the museum’s climate-controlled storage vault.

As with all treatments performed in the conservation lab, a final written treatment report with detailed before, during, and after photography is added to the museum’s database. Treatment reports are particularly useful when components such as the original brown tape have been removed or when the object contains multiple parts such as the plastic overlay. Maintaining a record of the original object and how it was modified allows future researchers and museum staff to understand how and why conservation decisions were made and may help inform future decisions for similar objects.

Bonsai Forever Stamp Series

The Bonsai Forever Stamp Series, sold in booklets of 20, went on sale at post offices nationwide on January 23, 2012. For each stamp design, artist John Dawson of Hilo, Hawaii painted a particular style of bonsai under the direction of art director Ethel Kessler. Unlike other works received in the most recent transfer of USPS stamp art, the Bonsai stamp art was glued directly to backing boards to support the relatively thin paper substrate. Previous attempts to separate the paper substrate from the acidic backing board had resulted in tears and uneven delamination of the backing board but no damage to the artwork. Treatment included performing a mechanical backing removal to separate the art from the backing board and then reattaching the artwork to a more stable acid free matboard backing.

The first step in repairing the bonsai art was to remove and retain the damaged overlays which made it difficult to see the artwork. Retention of the overlays was important because they contain pencil annotations that need to be preserved. The pressure sensitive tape used to attach the overlays was relatively new and could be removed mechanically without the application of heat or solvents.

The original acidic backing board had to be removed in order to prevent the migration of acids onto the paper, which would have resulted in discoloration over time. Testing the adhesive used to apply the backing board indicated that it was water soluble, but application of moisture to the backing board could have resulted in water damage to the delicate artwork, so it was decided to remove the backing board mechanically, using a paper lifting knife to carefully separate the backing board from the paper substrate.

Proper storage and housing of art on paper is essential to protect fragile painted surfaces such as the ones created for Bonsai Forever Stamp Series. In this case, custom made MicroChamber paper corners were used to secure the artwork to an acid free backing board which will be housed in an acid free paper folder for long term storage. The new backing board is cut to the size of standard exhibition frames, making it easier to mount the object for exhibition when needed.

When rehousing works of art on paper, non-adhesive mounts like the photo corners used on the bonsai art are a good choice to avoid damaging original materials. If more permanent mounts are necessary, such as Japanese style paper hinges adhered directly to the object, the object would receive further review by the museum’s conservator.

CONCLUSION

Beyond the conservation treatment procedures outlined in this post, proper storage in a climate-controlled environment is an essential component in caring for collections and something that all collectors should consider. The National Postal Museum maintains a stable environment of 70°F and 45%RH in most storage areas and monitors these areas daily to address any fluctuations. Light damage is minimized by storing materials in acid free folders and boxes inside powder coated steel cabinets.

The same level of care is taken when objects are exhibited: selecting acid free matboard, professional quality metal frames, and exhibition glass that will filter ultraviolet light. Exhibition rotations are limited to no more than six months. When objects are on exhibition, gallery light levels are maintained at 5 footcandles or less with generally no ultraviolet light. Daily exhibition checks with light meters ensure that light levels remain stable. The same standards are required of borrowing institutions when objects are loaned for exhibition, and detailed facilities reports are required before loan contracts are drafted.

Systematic preventive care combined with an active program of conservation treatment guarantees that the Postmaster General’s Collection will be available for generations to come. Examples from this remarkable collection may be seen throughout the National Postal Museum, including permanent exhibitions in the National Stamp Salon and temporary exhibitions such as Baseball: America’s Home Run.

Images appear courtesy of the United States Postal Service. © USPS; all rights reserved.