Samantha Springer Assistant Conservator of Objects
Colleen Snyder Assistant Conservator of Objects
Tall-Case Clock (Regulateur) 1744. Jean-Pierre Latz (French, 1691–1754). Movement maker: Stollewerck (French). Boulle marquetry with gilt bronze mounts; 261.6 x 69.9 x 41.9 cm. John L. Severance Fund 1949.200
When it came to the preservation of this 18th-century French clock, not only the magnificent case with brass and tortoiseshell Boulle marquetry and elaborate gilt bronze mounts required study and treatment. The movement and face also deserved equal attention as a part of the overall project. To provide optimal care for each of these components, the clock was disassembled and worked on in three different labs across the country. Conservators at the J. Paul Getty Museum specializing in French furniture attended to the case, while a horological conservator, or an expert in the manufacture and care of timepieces, focused on the movement. During the final step, all the parts returned to Cleveland, where we treated the clock face prior to reassembly.
To treat the case, including extensive documentation, stabilization of the marquetry, and overall cleaning, the Getty conservators employed both state-of-the-art and updated traditional techniques. For instance, a newly adapted gel based on the chemical composition and physical properties of Silly Putty targeted the removal of tenacious varnish residues. Following this, corrosion on the unvarnished brass was reduced with an animal glue peel—an established practice with new modifications. Like a “spa treatment” for the metal, the glue and additives cause a chemical reduction that minimizes corrosion blemishes on its surface.
During Treatment Small areas of the marquetry were held under pressure with an adaptation of a Japanese-style clamping system called shinbari while the adhesive used for stabilization dried.
One of the most innovative and exciting techniques in the conservation process was used to clean the clock’s numerous brass mounts. Instead of polishing, conservators used “CO2 snow”—micron-size particles of solid carbon dioxide shaved from blocks of dry ice—to evenly reduce pitting corrosion. CO2 snow should not be confused with commercial dry-ice blasting, which produces pellets that are millimeters in size. Instead, this novel treatment method passes a fine and controllable stream over the surface. This technique was especially useful for the mounts’ finely textured surfaces because it removed green corrosion product in recesses without altering the patina and surface color, thereby allowing the surface to look more like originally intended.
Test Cleaning The bright brass at the center of the image is a test cleaning spot. Once cleaning of the marquetry was complete, it was allowed to oxidize evenly and darken slightly to an acceptable level before a protective varnish coating was applied to arrest the oxidation process.
While work progressed on the case at the Getty in Los Angeles, the Stollewerck movement was across the country in Boston for an equally extensive investigation and treatment. The purpose of this work was twofold: first, to clean and decommission the mechanism; and second, to take advantage of the complete disassembly to fully document its unusual construction. One curiosity of the movement surrounds the use of a weight and a mainspring. Typically a clock is run by one or the other, but not both. In this example, a steel mainspring runs the strike train which sounds the hour bell. The spring is housed in a stationary barrel so it does not interfere with the pendulum’s movement. However, the time train which moves the hour, minute, and second hands is still run by an older technology weight. It is arranged so that it moves toward the front of the clock and away from the pendulum as it descends to minimize interference.
The Movement It keeps track of not only the time to the second, but also the day of the month, day of the lunar month, and phase of the moon. Here you can see the 11 bells of the carillon, each with two hammers, and the hour bell below.
The eccentricity does not end there. This clock is not just a regulator of time, chiming on the hour and half hour, but also a small music player with a carillon—a set of bells played by an automatic mechanism. The carillon plays 11 tunes, one each hour approximately 30 seconds after the hour bell strikes. Having 11 tunes alleviates the monotony of listening to the same song at each hour; a lever provides the option to silence the music when desired. By diagramming the movement and counting every tooth, we discovered that the clock could run for 45 days on only one winding! This far outran most other clocks of the era, which required winding every week.
Back in Cleveland, attention focused on the clock face, which had a degraded cellulose nitrate coating. Though cellulose nitrate is still used today as a protective varnish, most commonly on silver, its lifetime is limited and requires replacement. After we removed the coating, a chemical solution reduced the uneven and darkened gray appearance of the silver. The solution was used instead of a slurry of precipitated chalk in water, which could remove too much of the thin layer of silvering.
The Face The numerals, especially those on the top calendar dial, were difficult to see because of the tarnished silver around them. Degradation of the old coating allowed dark areas of tarnish to develop, such as the one above the Roman numeral XI on the dial. After cleaning, the coating was methodically replaced to ensure all surfaces were covered and to slow the future development of tarnish.
After so much work on the case and face, why not restore the movement so that it runs? The clocks in the CMA collection are displayed in a state of suspension rather than functionality for their long-term preservation, which is standard practice for art museums. Rather than replace original parts and put the mechanism at risk of future damage, we decided to bring the clock back to life by recording its functions with audio and video. Our work on the clock will not end there. So that our visitors can fully enjoy the aural components, we are collaborating with the department of music at Case Western Reserve University to identify the tunes and make them a part of the ArtLens app.
Special Thanks to Dr. and Mrs. Richard Distad and Mr. and Dr. Elizabeth Fesler for their support of the restoration project.
Cleveland Art, September/October 2014