When I was asked by Philip Glass to have a look at his Metamorphosis (originally written for solo piano) I was concerned it might not work very well on the harp.
One reason was that when you watch pianists perform these pieces there are sections where the right hand crosses over the left hand, in order to reach the bass notes. On the harp this is quite impossible, because of having the instrument in the way. So I had to think of a way to change the middle voicing, changing them back and forth between the left and right hand. This way I could catch the middle voice with my right hand, while I was playing the bass notes with my left hand. The tricky part was to leave the middle voice as flowing as possible, not hearing the switching of the hands.
The Hours was even more of a challenge, I wasn’t sure for a long time if this would work on the harp. I studied the orchestral score and the piano transcriptions and tried it out. What was more difficult in these pieces was the chromatic character of some of the movements, where I had to switch pedals very quickly. I had to adjust some notes, not in the pitch, but in the choice of which string to play it with.
You see, on the harp we can sometimes play the same note on two different strings. For example a C# can also be played as a Db, on the piano these are the same key, but on the harp these are two different strings. Another thing is that harpist only play with four fingers per hand, with fast scales that are played with five fingers on the piano, we need to adjust the fingerings for that on the harp.
On the other hand, having the orchestral score to be inspired by, I couldn’t resist to make a few adjust to imitate for examples the bells in the orchestra using flageolets on the harp (damping half of the string and playing the upper part, the result is a bell-like sound).