Technical Library

TROPICS III: Metalwork

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Galvanic string corrosion 57K jpeg
Galvanic string corrosion


Strings and tuning pins are particularly susceptible to corrosion with high humidity, and this can be worse in dusty or acidic environment where it can be observed that the corrosion tends to form on the upper surface of metal parts, rather than all around.

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Where two different metals contact it only takes constant high humidity for galvanic corrosion to occur: This is the principle of the electric battery, and higher temperatures accelerates the problem.

Of course, iron strings can generally rust, and as well as being unsightly, the tone is eventually affected along with the lifespan of the wire. Some ferrous wire is plated to delay the onset of corrosion.

Galvanic string corrosion 57K jpeg
String corrosion at contact with unsealed beech nut

Acidic woods
Another commonly-seen problem is caused by the acidic nature of most woods. Again, high humidity can cause string corrosion where the strings run across unsealed bridges or nuts. Brass-strung instruments are particularly susceptible, and the treble strings pop first because of their smaller diameter.

The cure is permanent: The strings are removed, the upper surfaces of the bridges and nuts sealed with shellac, and the instrument freshly restrung.

Galvanic string corrosion 57K jpeg
Corroded balancepins

Other hardware
Tuning pins and balancepins are also subject to increased corrosion with high humidity.

When balancepins reach this stage, they are obviously contributing to general keyboard sluggishness. They can be polished with fine steel wool and the balance mortise is again frictionless.

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Bullfrog emitter cup for corrosion inhibition

Prevention & treatment
We offer the Bullfrog corrosion inhibitor emitter cups. These inexpensive sealed containers last a year in an enclosed space, gradually dispersing vapor which coats metals and helps to protect iron strings and tuning pins from rusting. The cups are of limited use for the galvanic corrosion, or bridge contact corrosion problems.

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