Piano keys:
Depressing the key starts the lever system on the piano which ends up with the hammer striking the string.

Covering:
Keys were normally covered with African Ivory though cheaper pianos used a celulose plastic covering and from about 1920 plastic was increasingly used. Ivory is very uncommon from about 1960 onwards.

The first photo is a piano key seen from the side	The same key from above

Introduction:
The piano key is an essential part of the piano and mostly you only see the plastic/ivory part of the key. After the ivory ban in about 1989 manufacturers turned to plastic keys in order to continue production, hence pianos produced with ivory keys after the ban are virtually non-existent. However ivory has a distinct feel and is preferred by most pianists.

Grand vs Upright keys:
On an upright piano the key length of key is shorter than on a grand. On a grand, more length equals more leverage and ease of touch than on an upright. The action of a grand piano faces upwards so as to hit the strings, on an upright the hammers fall horizontally. The benefit of playing a grand piano is that you have control of the playing movement until it touches the string whereas on the upright action you can only control the hammer until about 2/3 of its journey.

Design:
The key acts a lever to transfer pressure from the pianists hand, activating the action, which throws the hammers towards the strings and makes a sound.

1. Key Depth (or 'dip'): this is the distance that the key can drop when played. This distance is normally between 10 and 12 millemetres and can be altered according to the desired touch of the pianist.
2. The length of key affects the amount of pressure that is needed to produce a certain amount of volume of sound. Many mini pianos have extremely short keys so the contol is severly limited. In contrast a concert grand by Steinway or Yamaha has a very long key and superb control.
3. Fitting: The key is held in place by two pins on the inside of the key, one acts as a pivot in the middle (the 'balance pin') and one at the front to keep the key from wobbling when played. This is called a 'cricket bat'.
4. Point of contact: The key has a tall metal screw at the rear called a capstan. This contacts the action and transfers the movement throught the lever to the hammers and onto the strings.
5. Weights: The piano contains lead weights (seen on the side of the key) this is to ensure that the keyboard has an even touch weight. Keys will be individually weighed on more expensive pianos once inside the keybed. Less expensive pianos may not include weights and most will not check the balance of weight after fitting the keys.