It is noticeable when studying Henry Purcell's use of lipped notes on natural trumpets that there was a preoccupation with the diatonic filling-in of gaps between the lower, triadic natural harmonics until 1693, after which interest in them waned and attention was directed at previously avoided higher natural-harmonics.
Movements 5-7 of Matteis's Concerto di Trombe include written-out mordents and turns on the triadic natural harmonics 4-6.(13) The embellishments have been viewed by Holman, Pinnock and Wood as evidence of additional string/woodwind parts that originally existed for the work but were not printed by Matteis.
The cello part is perhaps the most demanding of the four: to vary the natural harmonic
notes at his disposal, Amy calls for scordatura, retuning the C and C strings a half step lower.
The natural harmonics, and especially the "out-of-tune" 11th and 13th(or 14th) partials, should be explained to audiences, at least in the programme notes, so they do not conclude that the soloist is playing out of tune.
The flat 7th in bar 7 is preferred by some to be in tune, necessitating the same treatment as above (opening the hand), but I prefer it as flat as it is on the natural harmonic. Aim very low, as being the next harmonic from the open g will come easily if you don't aim too high, which could easily result in the note flipping up to the c".
the horn must use natural harmonics, which sometimes misleads listeners to blame the soloist for playing out of tune...
(18) Stephen Pettitt writes that it was Brain himself who originally suggested the use of natural harmonics for these two solo movements in the Serenade, (19) and Frank Lloyd speculates that Britten's notation could in fact be closer to what Brain played than we are giving him credit for: