Compared to the mechanism that propels the hammer toward the string, the wool felt hammers themselves look like pretty simple parts, right?
But in order for that hammer to have the necessary resiliency, durability, uniformity and length of wool fibres to get volume and an orchestral range of tone out of your piano, there are many considerations. The first one is the raw material.
Only virgin wool will do, which means the sheep has never been sheared before. This virgin wool is longer and contains more lanolin, a kind of wax in wool, than non-virgin wool. With each shearing, the wool contains less lanolin, making it drier and more brittle. Lanolin is a key ingredient in the resiliency of the hammer, which plays a huge role in tone.
So the wool is top quality virgin wool, and where this comes from can change year to year, as well, depending on the weather -- a particularly rainy season can impact the quality of the wool, for example.
I recently attended the Canadian Association of Piano Technicians convention at UBC where Melanie Brooks of Brooks LTD., a long-established company selling piano hammers, took us on a virtual tour of a felt manufacturer in Europe. First the wool is cleaned. Cleaning wool traditionally was done through a process called carbonizing, using sulphuric acid. This washes away all the "dirt, sand, dust, mud, vegetarian parts," as Norbert Abel of Abel Hammers explains. Carbonizing can also remove lanolin, so new techniques are used by Abel, for example, to create a "Natural Felt" hammer in order to retain the lanolin. The resulting hammer is not as white, but who cares?
Once it's cleaned, the wool is willowed, carded, combed and then felted. Basically, you take a fluffy mountain of wool, turn it into a giant mattress-sized fluffy piece of wool and then compress it down to a slab of felt the size of an atlas (remember those? Pre-Google-map).
The piano is such an amazing instrument that involves so many different skilled craftspeople and materials, and beauty-queen sheep. "What I can't bring to you," Melanie said after the final photo of the factory tour, "is the smell." And what is that? "A wet, wool sweater times a million in a factory full of heat and steam, day after day, after day," she laughs.
Once the slabs of felt are made, they are cut into triangular prisms with gradually increasing mass from one end to the other. This prism is the material for one set of 88 hammers, the higher mass end destined to become the bass hammers, and the lower mass end for treble.
Then on to pressing the hammers! I'll do a post just about that next.
I'm working with Ken right now to rebuild the action on a 9-foot Baldwin concert grand here on the Sunshine Coast. To decide what hammers to put on this piano, Ken must consider the size of the piano (those long strings need bigger hammers to get volume), the geometry of the action (to ensure we maintain the action leverage -- or, if the leverage was too high or too low to begin with, what kind of hammer we need to improve the leverage), and the design of the other parts (the hammers and shanks need to fit the wippens we'll be using, for example). I'll be posting a story about that, too, so you can see the before and after.