By Elly Stewart and Stephanie Guidera, summer conservation interns
The CMA’s galleries are dynamic and always changing. As the museum prepares for the reinstallation of the British galleries in November, objects are being carefully prepared for their new display cases and storage. One of the most impressive groups of objects in the collection are the ornate silver vessels. Learn more about the conservation process this collection undergoes in the essay below by summer conservation interns Elly Stewart and Stephanie Guidera, and check out the collection in person when the gallery reinstallation opens on November 24, and online in the CMA’s collection online.
Whether you have encountered your grandmother’s set of silverware or have seen silver tableware in a Downton Abbey dinner scene, it is clear that silver requires a lot of maintenance due to its propensity to darken, or tarnish, over time. These objects can also be very tricky to care for because artists applied various alloys, plating, and coatings to achieve the desired surface appearance. While most objects are solid silver, some are composed of other metals, mainly copper alloys, plated in silver. Decorative pieces also may have selective gold plating applied for a beautiful contrast between these metals. Finally, coatings can be applied to enhance or protect the metal surface. Due to these variations, the history and materiality of each piece must be observed to determine the best way to protect it. Art conservators spend many years learning the material science of art and artifacts in order to participate fully in the process of deciding the best solutions for the care and display of the collection.
Elly Stewart and Stephanie Guidera, summer interns in the objects conservation lab, are in two phases of art conservation education. Elly is completing the art history and chemistry pre-requisites necessary for admission into one of the nation’s four graduate programs in art conservation. Stephanie is a current student at one of these programs, the Garman Art Conservation Program at SUNY Buffalo State. Elly and Stephanie joined Amaris Sturm, Mellon Fellow and objects conservator, and CMA Objects Conservators Colleen Snyder and Beth Edelstein in assessing and conserving these objects. As silver care and polishing is a frequently requested topic, we decided to highlight our process within the beautiful silver collection.
Silver tends to tarnish quite easily due to the presence of sulfur in the air, causing corrosion through a chemical reaction. Although tarnish looks like something that accumulates on the surface, this corrosion is an internal breakdown of the exposed silver metal and its transformation into a dark silver sulfide. Sulfides are necessary for this tarnishing reaction, but over time even oxygen can cause objects to darken. High temperatures and humidity accelerate these reactions, as does contact with unstable materials. Certain materials emit chemicals that encourage corrosion; for example, wood, copper, and many types of fabric all will cause silver to tarnish more quickly. This may sound like a death sentence for silver; however, unlike rust, once the outer layers of silver are tarnished, the underlying layers are essentially sealed, which protects the silver from further damage.
Cleaning tarnish is simple in theory but can be quite difficult in practice. When removing tarnish from a silver object you are actually removing several microscopic outer layers of silver in the process. Some polishing techniques can even remove underlying untarnished layers or irreparably scratch the surface of the piece. It is also possible to over polish silver-plated objects, which reveals the base metal alloy underneath.
The silver objects in the collection do require occasional polishing by our objects conservation team. In the lab, we make a liquid solution of a very pure, conservation-grade calcium carbonate (chalk) powder and use soft, lint-free cloths that gently remove the tarnished layers without abrading underlying untarnished silver. Powdered calcium carbonate can be very dangerous if inhaled, so we make sure to wear respirators or dust masks to avoid breathing the powder. We also always make sure to wear the appropriate gloves in order to keep natural oils far from the silver and to protect our skin from the abrasives.
Art conservators do not use commercial polishing products for a number of reasons. Many products are much more aggressive than necessary, especially for silver-plated objects, increasing the risk of polishing away too much material or breaking through the plating. Overpolishing also runs the risk of removing engraved design or inscriptions over time. Most commercial polishing products also leave residues behind that make their way into the pores of the metal, causing permanent damage. Commercial products can also contain abrasives that claim to more easily remove tarnish but are simply too coarse, leaving deep scratches in silver that cannot be repaired and will cause tarnish to build up deep within the scratches.
Some silver objects are composite objects with different materials incorporated into their ornate designs. Gold is frequently added and it is important to note that gold does not tarnish and therefore should not be polished, but can be wiped to remove oils or residues. Extra care must be taken when polishing composite objects to ensure that no polish or residue comes in contact with the other materials, such as wood handles.
Many museums will coat silver with a clear lacquer to protect the surface from tarnishing. However, applying lacquers may result in a dulling of the shiny surface. At the CMA, we do not coat our silver pieces but design the display cases to protect the objects from environmental attack. Objects are sealed from pollutants in the open air, and the museum environment is humidity and temperature controlled. Lastly, the objects are displayed on fabrics that have passed scientific tests proving that they will not release any tarnish-accelerating chemicals. The silver objects not on view are similarly protected in our temperature-, light-, and humidity-controlled storage facilities.
From museum display to a family heirloom, the goal is the same: protect and retain the intricate metalwork and shine of these objects. We are grateful for the opportunity to share a bit about conservation and hopefully, it will inspire you to look closer at these immaculate objects in their cases.
Special thanks to Steph Guidera and Joan Neubecker for taking wonderful images for this blog post! And a big thank you to Ben Davis for the animated before-and-after gifs!