Felt is one element of the mechanics in a piano, but is it a small element or a big one…
The finest hammer felts produced for pianos are made from virgin wool. It is classed as virgin wool when it comes from the very first shearing of a sheep.
Virgin wool contains the longest fibre and greatest lanolin content, it can be removed from each sheep only once. This is the reason that it is very rare and very expensive.
Each shearing that takes place post the ‘virgin shearing’ produces a wool that is drier and more brittle, this is due to the Lanolin content being lower.
|What Is Lanolin
Lanolin also called wool wax or wool grease is a yellow waxy substance secreted by the sebaceous glands of wool-bearing animals. Most lanolin used by humans comes from domestic sheep breeds that are raised specifically for their wool. Lanolin is a wax. Historically, many pharmacopoeias have referred to lanolin as wool fat; however, as lanolin lacks glycerides, it is not a true fat.
Certain breeds of sheep produce large amounts of lanolin, the extraction can be performed by squeezing the sheep’s harvested wool between rollers. Most or all of the lanolin is removed from wool when it is processed into textiles, such as yarn or felt.
Hammer felt is categorised by weight in pounds; this is measured by weighing a square yard of the primed felt. So when you read about 18 pound hammers you will know that it refers to the weight of the square yard it was cut from rather than the weight of each individual hammer.
In the construction of a hammer there is a wooden base, the felt is mounted onto the wooden hammer under great pressure. Tension must exist in the hammer felt to offer a resilient bounce off the string after it has been struck. Too much tension or not enough is a negative and can stifle the tone production.
Frequently manufactures use a thin layer of colored felt that they attach to the wooden hammerhead before attaching the final white/cream coloured felt that touches the string. This felt is called the ‘under felt’
The theory behind ‘under felting’ is one that piano makers, sellers and players are still divided on. Some believe that it adds to the overall experience whilst others believe it is a gimmick and the process of under felting is not necessary.
All hammer felts have to be glued to stabilise the felt to the hammer, in most cases they are glued and stapled
So now at your next ‘piano party’ you can spread your knowledge about piano hammers!
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