Bird quill is unquestionably the authentic material for plucking harpsichord strings. The sound is marginally different compared to Delrin, apparently emphasising the fundamental; the differences will be more easily noticed on the front 8' or 4' register, especially of an iron-strung instrument. Furthermore the touch of quill is noticeably better than Delrin, with more sense of contact with the string and control of the plectrum until the moment of plucking, although this aspect is seldom mentioned.

However, quill has the reputation of being sensitive to changes of temperature and humidity. This problem appears to be mainly due to the choice of quill material. I have found swan feathers to yield durable quills, just as Martin Skowroneck has already reported, and senstivity to humidity and temperature has not been a problem.

More disquieting for daily use in the initial phase is that the plucking strength of quill often suddenly becomes much harder. This has hindered many from using quill plectra in favour of Delrin. My recent investigation of the changing touch has shown that it is possible to maintain an even plucking strength over the entire initial phase if the quill is treated only on the underside with a suitable oil. Furthermore, the wear on the quill is much reduced. Applying oil to the top surface produces different and inferior results. Thus, a strategy is available to eliminate one of the major disadvantages of bird quill plectra.

For the essential facts about quill performance and maintainance strategies the harpsichordist can employ read here     or    download

For more information about the causes of variable touch, the effects of different treatments, oils and their testing  read here   or    download

Reference: Martin Skowroneck. Cembalobau (Bochinsky, Bergkirchen, 2003), pp. 89-94 (in German), pp. 226-228 (in English)