In Britain key tops were traditionally glued on with -- you might have
guessed! -- gesso, the creamy mix of non-crystallising animal glue,
whiting and just a touch of tallow.

Not only is this a very white adhesive which, showing through, won't
spoil the colour of the key tops, but most importantly it provides a
thin but total interlayer which stops any distracting finger tapping
during playing.

It also allows natural differential movement between the wood and
covering, though if the piano is well and truly cooked even gesso
can lose its adhesion.

Using gesso, clamps should be used, though heating them is unnecessary.
Gesso cools somewhat slower than simple hot glue and warms the wood
making a good bond.

I might add that I have little objection to using modern materials
and adhesives, always providing that they are absolutely properly used,
and that no permanent bonds are made, e.g., with epoxy or industrial
strength cyanoacrylates where parts must in future be dismantled.

Professional-quality silicone adhesives with a short tack time, for
instance, correctly used are very effective in some applications and
can easily be eliminated if the substrates are correctly prepared,
or with a harmless chemical remover.

Despite the traditionalists' insistence on hot glue (which I adopt when
truly appropriate), how many use it correctly, employing hot cauls,
hotplates and hot-cupboards like the original manufacturers to heat
parts thoroughly for assembly?  I've encountered too many cold joints
which have crystallised and have little strength to be easily
impressed.

Patrick Handscombe
Wivenhoe, Essex
UK