With the piano becoming so popular that every genteel drawing room had an upright, so did the demand for ivory, which had been used to cover the keys since the early 1700s.As time went on–and the Great Depression of the 1920s hit–many manufacturers began using plastic in place of ivory, as it was a less expensive alternative.
For example: "Hamilton" by Baldwin or "Cable Nelson" by Everett.
On the Piano History If you open the top of a piano and peer inside, you will often find one or more numbers in there.
Sometimes, they are harder to see, and may be underneath a grand.
Although it’s likely to have been a type of harpsichord rather than an instrument with hammer keys, the idea was born from there.
The piano didn’t really catch on as a popular instrument until the 1760s, aided by the rather prolific Bach family.