Probably the most neglected aspect of piano service is "voicing," that is, controlling the quality of the tone the instrument projects. It's easy to get the concepts of voicing and tuning confused. Piano tuning is adjusting the tension of the strings to set them at the proper pitch. Voicing is working on the texture and density of the hammer felt and on the hammers' fit to the strings to create the most beautiful sound. I get some calls every year from clients who are not satisfied with someone's piano tuning. When I hear the pianos it is sometimes clear that the piano tuning is ok, but the voicingof the piano has been neglected. The clients say their piano sounds tinny, uneven, thin, or even squidgy! I can help them by voicing the instrument.
Piano sound is half tuning and half voicing. Many of my clients call and ask to make an appointment for "piano tuning and voicing" because they have learned how vital voicing is to their needs. The most important part of voicing is communicating with the players. I listen to the pianists play, watch their techniques and discuss the tone before making any decisions. Some players prefer a bright singing tone, other a subtle, warm sound. Most good pianos are capable of either.
In practice, I start voicing even before I begin tuning the piano. During the course of a voicing job I level the strings with a small bubble gauge, tune, deep needle the shoulders of the hammers, shallow needle the strike points, and file the hammers to fit the strings. The final result is even, clear tone that suits your musical taste, with or without the una corda pedal in use.
Lacquer or shellac can be used to harden hammers that are too soft. Most of today's hammers are too hard so it is seldom necessary to add such hardeners. Steinway hammers are the exception. The addition of lacquer is factory practice. I don't like to argue with people who say the use of lacquer is undesirable. Steinway pianos can sound just fine.