Verdigris
Important Prerequisite Information
Piano action parts pivot on a hinge-like pin, called a center pin. This metal pin is held inside of a felt or cloth bushing, which has been properly sized so that an ideal amount of friction exists at this fulcrum point. One of the chief goals in action construction is that there is a controlled amount of friction at each center pin. Each key should respond similarly and consistently if the same amount of force is applied. Too little friction and the pianist will find the piano inconsistent and difficult to control. Too much friction and the piano will be tiresome and cumbersome to play. If friction is extremely excessive, parts can be slow to react, or completely seize up and become unmovable.​
Yamaha hammer assembly with a healthy, verdigris-free center pin.
1920s Steinway whippen with a verdigris-infected flange center pin.
What is Verdigris?
Beginning in the early 1900s, many American piano factories treated their wooden action and damper back action components with a moisture-proofing paraffin solution, in an attempt to prevent these parts from becoming brittle as they aged. Steinway’s New York factory implemented this procedure from the early 1900s to the mid-late 1940s, although other brands such as Knabe and Everett were also known to do this.
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As time went on, these manufacturers realized that the solution used to treat the wooden components would seep into and contaminate the center pin bushings, causing a green sludge-like oxidation of the center pin, called verdigris. Verdigris drastically increases the friction at these critical pivot points, negatively impacting the piano’s playability and responsiveness. To make matters worse, some verdigris has been known to contain toxic copper compounds.
Most piano manufacturers ceased treating their action components with the paraffin solution before 1950. Thus, verdigris has not been a problem in the majority of pianos manufactured since then. In rare scenarios, certain chemicals used during the piano refinishing process have been found to cause verdigris. If you are considering having your piano refinished, ensure that you hire an experienced specialist.
The Remedy for Verdigris
There is no known cure for verdigris-infected components. For almost a century, piano technicians have experimented and continue to experiment with chemical treatments, lubricants, and various other methods to reduce or eliminate verdigris. While some methods have occasionally had temporary success, the only permanent and effective solution for verdigris contamination is to replace the action components entirely. A colleague in Northern California has an excellent webpage on verdigris, complete with step-by-step photos of the problem, and the process of replacing the action parts.
1920s Steinway hammer assembly with a verdigris-infected center pin.
If you are considering purchase of an American piano made between 1900-1950, particularly a Steinway, it is important to consult with your piano technician and have them perform a technical inspection of the piano prior to your purchase. The technician can check the piano for signs of verdigris so you are aware if it is present before you purchase. If you already own a piano with verdigris, contact a reputable piano technician or piano rebuilder to inspect your instrument and advise accordingly.
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