Did you know –
The C# trill key can also be used to provide a more stable and colorful middle C# when activated while B-natural is fingered.
Trills
B-C# (first and second octaves): Finger B and trill the C# key.
C-C# (first and second octaves): Finger C and trill the C# key.
High F#-G#: Finger high F# and trill the C# key.
High G-Ab: Finger high G and trill the C# key.
High G-A: Finger high G and trill the C# trill key and D trill key in unison.
High Ab-Bb: Finger high Ab and trill the C# trill key, the D trill key, and the D# trill key in unison.
Tremolos
In the first octave, tremolo to C# from G, Ab, A, Bb, B, or C by trilling the C# trill key.
In the second octave, tremolo to C# from A, Bb, B or C by trilling the C# trill key.
In the first octave, tremolo to D from G, Ab, A, Bb, or B by trilling the C# trill key and the Db trill key simultaneously.
In the first octave, tremolo to D# from G, Ab, A, Bb, or B by trilling the C# trill key and the D# trill key simultaneously.
This fingering information is also shown on –
https://www.flutacious.com/Csharp-Trill-Key-Blog
Which includes this musical comment:
“Another famous use of the key was inspired by Claude Debussy’s “Prelude to the Afternoon of the Faun,” wherein the flutist fingers B and depresses the C# for more control and color on the opening C#.”
C# TRILL FINGERING CHART FOR THE PICCOLO
Yes! Keefe Piccolos of Boston have a C# trill key option for their piccolos.
This link shows you the trill fingering chart and some additional alternate fingerings with this key on your piccolo.