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It's standard that the front face of black keys on the piano are sloped away from the musician. Why is that?

The manufacture would seem simpler and cheaper if the black keys were square-cut like the white keys, and there are other designs, such as a rounded top-front edge, that would be more comfortable (than a square edge) to play.

How did the sloped face come to be, and why?

(N.B.: Looking at some harpsichord photos, it seems clear that the design preceded the invention of the piano.)

Cristofori keyboard (Source: Metropolitan Museum of Art)

1720 pianoforte with sloped key faces

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  • Are you assuming that a simpler/cheaper fabrication should have precedence? The purpose of an instrument is its sound and playability. Besides aesthetics, most instruments have physical aspects based on either acoustic and/or technique requirements, and, as with any evolution, what matters is the "successful" capacity considering those priorities, including inherited aspects (that's why even most modern keyboarded electronic instruments still follow similar shapes, as pianos did after harpsichords and organs). [Note: I'm not criticizing the question, just an apparent bias of its exposition].
    – musicamante
    Commented 11 hours ago
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    @musicamante What my post is saying is that clearly simpler and cheaper was not the motivation, so what was?
    – Aaron
    Commented 11 hours ago
  • Ok, I probably didn't read it that way, my fault. That said, I'm curious, as you probably are, not specifically about the "why" (I could give many relatively valid reasons, also enforced by colleagues more qualified than me), because it seems relatively obvious to me that the current design is probably one of the most effective (and it certainly is against drastically different ones, even ignoring established conventions), but if there's a canonical and reliable reference about that "evolutionary choice". For instance, there are many cases in keyboard based electronic instruments that »
    – musicamante
    Commented 11 hours ago
  • » are commonly (even though unofficially) known as "bad design". Most of the times it's about established conventions for keyboard players (used to piano keyboards), but sometimes it's just about pure practicality. I, for myself, do not like completely rounded edges, because it clearly lacks the physical perception of the "black" keys boundaries. OTOH, the relatively squared shape of "white" keys is relatively obvious in my opinion: based on the position of the hands and their fingers relative to the key geometry, using a slope wouldn't provide any real benefit.
    – musicamante
    Commented 10 hours ago

3 Answers 3

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When a keyboard key is pressed down it doesn’t move completely vertically, it rotates about the fulcrum.

If the corner of a black key wasn’t bevelled, the front face of the key would protrude slightly forwards when depressed; it would jam into the back of the notch of the adjacent white keys.

Simplified geometry of a piano key rotating about the fulcrum. As the key is pressed down the front edge leans forward slightly.

This could be overcome by leaving a larger gap between the keys when unpressed, but that wouldn’t look very nice.

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  • This was also my thought, until I started looking at harpsichord keyboards. Some were clearly beveled, but others appeared to be square. Here's an image of a dual-manual piano that appears to have square key-fronts: istockphoto.com/photo/…. However, it's hard to find images in which it's clear that the keys are square and not just very slightly beveled. I suspect there's an aspect of playing comfort or other consideration beyond just the matter of geometry (and aesthetics).
    – Aaron
    Commented 9 hours ago
  • FWIW, another way to think of the geometry issue is that the fulcrum, lower-front key edge, and upper-front key edge for a right triangle. The rotation over the fulcrum creates to arcs — one for each edge — but the radius of the upper key edge, being one end of the triangle's hypotenuse, is longer than that of the lower edge. Your image shows the same idea in a very elegant way.
    – Aaron
    Commented 8 hours ago
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    While the effect described in this answer is real, it's small, as the piano key length to the pivot point is much longer than its vertical dimension, and its range of motion. I don't believe it explains why the edges of black keys are sloped as much as they typically are in a piano.
    – user1079505
    Commented 8 hours ago
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    @JimM You can see the effect on the white keys, but there is nothing in front of them to jam up against.
    – Elements In Space ♦
    Commented 4 hours ago
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    @Aaron there's a substantial gap in front of the "black" (actually white) keys in that photo, which confirms the statement "This could be overcome by leaving a larger gap between the keys when unpressed"
    – fdomn-m
    Commented 46 mins ago
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Quite possibly not the actual reason, but a good by-product. It makes it easier, smoother, to slide from a black key to the next white key - something I seem to do fairly often. If the edge was perpendicular, this would be not as easy.

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Catching a fingernail on a right-angled edge of a black key while playing a fortissimo passage would seem like an unpleasant experience. Also a sharp edge will dull out much faster. This will look shabby particularly if the color is mainly from dyeing rather than a natural hue.

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