[...] I am now beginning preparations—for honour's sake—for the performance of Parsifal. We were unlucky with our English dragon, and we must see whether we cannot do better with the Grail bells.
After discussing with experts the best way of representing the chimes, it was agreed that they were best imitated by Chinese gongs. Well then, in what market was the best choice in quantity and quality of these gongs to be found? In London, it is suggested. Good! Who will undertake the choice? Dannreuther, of course! Well, dearest friend, see if you can scrape together four gongs giving—as near as possible—the following peal: [...]
Note that, to elicit a deep bell note, these instruments should be struck very gently on the rim, whereas if they are struck sharply in the middle they give a ringing and quite useless note. Well then, see what you can do! [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 723