Caring for Brass & Bronze (Part I)

Article for MCHS newsletter, Vol. 22, No. 4, 2009.

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Imagine the panic. After decades of use, over half a century from my family alone, our beloved 1903 Segerstrom upright piano developed green spots on the pedals, seemingly overnight. Made of brass or brass-plated steel, a relatively stable and hard-wearing material, the pedals appeared in great shape until those dreaded green spots appeared. While there, unfortunately, is not a good metal fairy who can waive her magic wand and make the damage disappear, an abundance of resources are available regarding the care and preservation of metals. Thankfully, with some basic maintenance, stable brass and bronze objects can retain their good health and integrity.

The three main causes of damage to metal objects are corrosion, mishandling and poor environment. The environment in which a brass or bronze piece is used or stored plays a significant role in its health and longevity. Moisture can be particularly destructive, making most basements a less than ideal surrounding. Keeping humidity levels below fifty-five percent and avoiding rapid fluctuations in temperature is essential. Temperature changes cause metals to contract and expand, weakening the surface and encouraging protective coatings to fail. Air pollution, such as car exhaust, cigarette smoke, dust and debris, are also destructive. These can accumulate on the surface, attracting moisture and encouraging corrosion. If a brass or bronze piece is to be stored, choose metal cabinets and shelving over wood as wood produces harmful vapors and acidic gasses. Avoid using newsprint and cardboard boxes, both of which are acidic, for packing materials. Purchase acid-free, lignin-free paper and boxes or other inert packing materials, such as expanded polyethylene or Ethafoam. For a simple and economical packing material, use clean soft cotton cloth.

Mishandling of a brass or bronze object can cause denting, breakage, bending or cracking. Avoid lifting the object by extended areas, such as a spout, lip or handle. Also avoid skin contact. Oils and acids from human skin will invariably be left on metal surfaces, causing corrosion and pitting. Wear clean cotton gloves or use a clean soft cotton cloth when handling. If objects do come into contact with bare skin, be sure to clean carefully after each use.

For stable brass or bronze objects, a few simple cleaning procedures are key to maintaining their health. Vacuum regularly using a nozzle attachment with a brush to remove dust and dirt particles. A soft artist’s brush or toothbrush will help with crevices and hard to reach areas. Surface grime can be removed with a two to three percent solution of plain soap or mild detergent, such as Orvus, and deionized or distilled water. Orvus can be found at most veterinary supply or farm stores. Rinse carefully with deionized or distilled water and dry completely with unbleached cotton flannel or other soft cotton lint-free cloth. If the surface dirt is particularly greasy, use a three percent solution of Vulpex, a liquid soap sold by most conservation suppliers, in mineral spirits and rinse with straight mineral spirits. Calcareous (lime or hard water) deposits can often be treated successfully with a ten percent solution of regular Calgon (sodium hexametaphosphate) in distilled or deionized water. Allow the solution to soak in and then carefully rub with a stiff brush to remove. Rinse thoroughly in distilled water.

Each time a metal object is cleaned, some of the original metal is lost and the surface may be scratched or abraded, causing damage to any decorative detail. Always exercise caution when cleaning a brass or bronze piece and weigh the benefits before proceeding. Collection Connection: Caring for Brass and Bronze (Part 2) will cover how best to polish your piece and remove active corrosion. It will also reveal which “procedure” was chosen for the Segerstrom piano pedals and if the benefits outweighed any resulting harm.

By Ann Marie Johnson
Copyright 2009, Morrison County Historical Society

Sources:

“Appendix O. Curatorial Care of Metal Objects.” Museum Handbook: Part 1 – Museum Collections. Washington, D.C.: National Park Service, 1990.

“Caring For Your Treasures: Metal Objects – How To Protect Your Metal Objects.” American Institute for Conservation of Historic and Artistic Works (http://www.conservation-us.org).

Deck, Clara, Senior Conservator. “The Care and Preservation of Historical Brass and Bronze.” The Henry Ford (http://www.thehenryford.org).

Long, Jane S. and Richard W. Caring for Your Family Treasures. New York: Harry N. Abrams, Inc., 2000.

The National Trust Manual of Housekeeping. Oxford, UK: Butterworth-Heinemann. 2006.

Williams, Don and Louisa Jaggar. Saving Stuff: How to Care for and Preserve Your Collectibles, Heirlooms, and Other Prized Possessions. New York: Simon & Schuster, 2005.