Gold–plated Pig Guts

In the "Electrostatic History" section of the MartinLogan owner's manual:

Bell Laboratory's electrostat was something to behold. This enormous bipolar speaker was as big as a door. The diaphragm, which was beginning to rot, was made of a pig intestine that was covered with fine gold leaf to conduct the audio signal.

This was around 1923. I didn't know electrostatic speakers had been around for so long.