Impregnation

Nitro thinner or synthetic, depending on the case... the second is better as it doesn't spread the color of the under-felt...

But I don't understand what experiments can be done on current European hammer heads, which is rare, if not inadvisable, to have to impregnate since they are hammers that are already born quite compressed and tense.

What is obtained by impregnating this type of hammer, in very diluted doses because otherwise the impregnating substance cannot even penetrate, is nothing other than a decompression of the felt, due to the fact that the thinner, being liquid, acts by swelling the felt before evaporating...

The substance that remains, whether it be nitro clear varnish (or zaponlack) or collodion (nitrocellulose), contributes to generating a brighter attack because it "glues" the fibers together more than they already are, but not to build tone since the hammer felt is already born compressed, precisely, and it is the decompression that makes it sound, whether this is obtained through puncturing (and subsequent shaving) or with nitro.

Different is the case of a very soft hammer felt, in natural felt, where the impregnant can penetrate deeply even in low diluted doses, and with successive applications that are progressively more diluted to build body and attack... as in the case of the American Steinway hammer....

Then there are those who use very diluted impregnant distributed uniformly on the felt, and those who use a denser one but only on the shoulders with the aim of tensioning the felt more...

In my opinion, today one must start from proper hammer voicing/regulation, setting aside (outdated) impregnation techniques, limiting them only to the treble wedges if necessary.

No of course, regarding the European hammer it doesn't seem like the case, it's a separate idea for later, USA....