The Celtic harp is what most people think of when they think of a folk harp. It is a very ancient instrument; harps of one sort or another have been in constant use since about 1500 BC. The Romans are thought to have introduced the harp to Britain in around 50 BC, and by around 400 AD the harp had spread across the British Isles in a variety of forms which are recognisably the forerunners of the modern Celtic harp.
All Celtic harps have certain features in common. Firstly, they are tuned diatonically, in other words the strings sound the same as the white notes of a piano. This is fine until you want to play in a key other than C major or A minor, when you need the semitones - the ‘black notes’. This is the second feature common to Celtic harps; they all have some way of raising the pitch of individual strings to the next highest semitone. If you raise all the F strings so that they sound F sharp, for instance, you can play in G major and E minor. In theory it would be possible simply to retune, but in practice it would take far too long to do this, and in any case many tunes use ‘out-of-scale’ notes, or accidentals, right in the middle of a passage.
The solution is to fit sharping levers. They sit just below the bridge pin on each string, and when raised each lever raises the pitch of its string by exactly the right amount. The levers that I fit to my harps are solid brass. They are made by hand in the workshop to a design worked out over many years by my father. I normally fit a lever to every string, as this gives the maximum possible flexibility to the instrument.