<HTML>            List          There are different kinds of plastics that yield decidedly different results. For example I have used clear plexiglass in an acetone solution for years on Isaac,Ronsen and Steinway hammers. The plexiglass is not  nasty and unforgiving as the keytop/ acetone solution is and frankly almost never use it. As you said David keytop/acetone  it is not for building tone it's for quick evening out of tone usually in concert situations. Iwould not recommend plexiglass for building tone in the steinway hammer either. But would use it to even things out.   In fact If a hammer tends to be notoriously soft as many stwy hammers (and others) are the best tone building solution is an appropriately dilute solution of sanding sealer or clear laquer. Plexiglass will adequately build tone in hammers that are closer to what most of us would call acceptable tone without the danger of ruining or over polluting the hammer.  The whole idea of voicing is control over  felt stiffness appropriate for the impedance characteristics a particular soundboard system .    Dale Erwin</HTML>