Glass

What it means

Under the heading glass, instruments are grouped in which glass bodies serve as sound generators. Best known is the glass harmonica: on a horizontal axis sit nested glass bowls of different sizes, set in rotation by a pedal; the player touches their rims with moistened fingers, and the friction produces a sustained tone. Beside it stand glass instruments made of individual goblets, which are tuned with water and likewise rubbed at the rim or struck, as well as glass-rod instruments played with mallets.

Musical use

The sound is poor in overtones, soft, and floating, without a distinct moment of attack; it seems bodiless and is hard to localize, which since the eighteenth century contributed to its reputation as unreal. After a heyday in the late eighteenth and early nineteenth centuries the glass harmonica largely fell out of use but was rediscovered in the twentieth century and received new repertoire. In the orchestra it appears rarely and usually with sparing accompaniment, because it is quiet and vanishes at once in a dense texture. For similar colours, composers today occasionally also reach for bowed crotales or the celesta.

Performance practice

Keep the fingers and the glass rims clean and moist; grease and dust prevent the friction and make the tone dull. The pressure must be very even — the volume arises from it, but too much produces a squeal. Expect a run-up time until the tone stands, and plan it musically. Damping happens by removing the fingers but acts sluggishly, which is why dense chord changes blur. With glass instruments tuned with water, check the fill level before every performance, since evaporation changes the pitch. Always transport the instruments packed shatterproof.

Remember that the sound is very quiet and easily vanishes in the concert: settle scoring and placement so that the instrument stands close to the audience and the accompaniment stays thin. With amplification, the miking is tricky, because incidental noises of the mechanism are picked up as well. Keep water and a cloth ready and avoid hand cream before playing, because residues reliably prevent the friction.