Welcome to the Prismatarium

The Prismatarium mural during treatment, approximately halfway through grime removal.

This brightly colored room can be found in the western end of the Bathhouse Building (aka the Maritime Museum) of the San Francisco Maritime National Historic Park. Hilaire Hiler, the man behind the spectrum, referred to the space as the Prismatarium: he wanted visitors’ experience within the room to be similar to that within a planetarium, that is, an educational transportation to his world of color. Hiler was a psychologist and color theoretician, and in the late 1930s he was hired by the WPA as the chief artist for the Maritime Museum. From gorgeous murals and mosaics to maritime-themed doorhandles, the building is an exquisitely designed public tribute to the San Francisco bay and to American artisans. The Prismatarium is a circular room with floor-to-ceiling windows looking out to the bay. Its ceiling is a mural of Hiler’s own 30-step color wheel, which he developed by defining sensational, rather than mathematical, differences in hue.

During the 70+ years since its creation, the Prismatarium developed some major condition issues, the most visually disturbing being a heavy build-up of environmental grime from the busy surrounding city. This, combined with light exposure and a yellowed coating, left the once vibrant ceiling as a dismal version of its original presentation. The National Park Service decided it was time to do something about this problem and hired San Francisco-based conservator Anne Rosenthal to care for the artwork. Anne, in turn, took on my classmate Samantha and I as interns for two weeks to help her with grime removal.

70+ years of grime — gone, with the stroke of a gel-soaked sponge!

Cleaning a painting is rarely simple (and should only be attempted by qualified personnel!). In this case, solubility tests revealed that water removed color along with the grime. However, solvents that could remove grime without disturbing the paint layer were not appropriate for use in a public space due to their toxicity. This is where a conservator’s training in chemistry comes into play. At the appropriate pH (acidity), polymeric acrylic acids cross-link to form a gel that is capable of suspending water without altering its chemical properties. This gel can then be brought briefly to a sensitive surface, such as that of the Prismatarium, and the suspended water draws the dirt away without ever interacting with the paint! It’s like magic… or science.

After two weeks of mixing gels by the gallon, driving scissor lifts in circles, and cleaning the ceiling while simultaneously toning our triceps, the Prismatarium revealed the gorgeous colors that had been hidden for so long. Although we exceeded our goals for the two weeks, Samantha and I had to leave before the entire project was complete, so I can’t dazzle you with a full “after treatment” image yet. The good news is: the Maritime Museum has free admission, so next time you’re in San Francisco, stop by and check out this profound example of WPA craft and design in person!


The main exhibit hall of the Maritime Museum, with more murals by Hiler.

The balcony of the museum which faces the San Francisco bay.


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