Piano keys were originally made of ivory, not only because of its value and because of aesthetic quality, but also because its properties allow it to absorb perspiration. Thus, keys made of ivory, unlike those of plastic, would reduce the chances of the pianist’s fingers slipping. Due to animal protection laws, however, ivory has not been widely used in the production of piano keys since approximately 1950. If you own a piano that was manufactured in the last 50-odd years, it is highly improbable that it has ivory keys.
How to Determine if Piano Keys are Ivory: Hot Needle Test
Use a needle that has a very fine, sharp point. Hold the point of the needle over the flame of a lighter until it glows red hot.
Press the glowing-hot needle against a portion of the piano key that is least visible, in case of damage.
If the needle melts a tiny hole into the piano key, it is made of plastic or some other type of synthetic substance. Unlike plastic, an ivory key cannot be penetrated.
The Ultraviolet Light and Magnifying Glass Test
Hold an ultraviolet light above the piano keys. If they are made of ivory, the keys will luminesce either white or with a violet-blue color (See Ref. 1). If you do not have access to an ultraviolet light, skip to Step 2.
Piano keys were always made out of three separate pieces of ivory; two on the top surface, where the fingers are placed, and one covering the small, front section. Use a magnifying glass to look for a very fine line where the two sections on the top surface join together (See Ref. 3). If no line exists, the key is most likely made out of one piece of plastic or other material.
Use the magnifying glass to look even closer. Ivory contains Schreger Lines (See Ref. 1), which will appear as a tiny pattern within the ivory, not unlike a fingerprint.
Ivory will tend to yellow with age. If your piano keys have a yellowish look about them, they may be made of ivory.
Do not use the hot needle test if you adverse to lightly damaging your piano key.