Much attention has been focused in the last couple of years on the remarkable variety of registrational resources available to keyboard players in the late 18th Century in the German-speaking countries. One thinks of the most obvious example, pipe organs, but fortepianos and tangentenfluegeln also depended on these devices at that time for a large portion of their tonal variety. The early piano was not yet capable of the same degree of loud and soft expression as the clavichord, the tangi even less; particularly the latter depended on a surprising array of mechanical devices to provide variety of sound. Pianos we find rather often had unleathered hammers with a moderator stop to produce the softer sound with which we are more familiar.
But then what happened? The century turned and the instruments were changing; tangis drop from view and fortepianos virtually always now had leather covered hammers. Loud and soft expression was slowly increasing as pianos became larger and the actions more pliable. Viennese players continued to prefer the fast and light touch and tonal clarity of their own instruments, but the taste of the times continued to strive for additional variety and color possibilities. Instead of a rush to a heavier action and deeper touch to achieve more volume and loud-soft contrast, the Viennese makers for a couple of decades exploited the designed-in coloristic variety of their instruments, which could change from bass to treble as well as from heavier to lighter playing, and to this they considered it essential to add stops, veranderungen, as had their 18th Century predecessors.
We have much documentation for this: the little introduction to fortepianos and their playing by the firm Dieudonné and Schiedmayer in Stuttgart describes the various pedal possibilities at length, insisting that any good piano provides these and criticising the English instruments, for all their other virtues, for omitting most of them; though the Turkish music was generally frowned upon as being in bad taste and children¹s toys, many of the surviving instruments had this feature and there is documentary evidence of Beethoven himself being overheard furtively experimenting with this effect. Almost all the surviving instruments from 1808 to 1830 or so have numerous pedals, commonly not only damping and a moderator, which sometimes had two levels, but a bassoon stop, coupled to have the moderator play as well. Some of the finest had a true una corda. The Dieudonné and Schiedmeyer book describe this specifically and the Streicher instruments from this period all have both una and due, sometimes with a separate pedal for each. A very soft sound indeed is possible by combining these various pedals. References to the use of these stops is unfortunately rare in written music; we¹ve become used to Beethoven without stops though he¹s the one composer who actually indicates these in a few places in his piano music. To hear Schubert and von Weber with these effects is quite convincing however.
By mid-century, this line of musical expression was overwhelmed by the striving for greater volume; the modern piano has little else to offer.
"Briefly, the evidence is very slight, but e.g. the lute stop was commonly used in France, with the sustaining pedal(!). Dussek appears to advocate the use of the una corda in his manual. Beethoven's notation for the use of the una corda is well known, but the "senza sordino" at the beginning of the Moonlight Sonata is more likely to refer to "no moderator"(sordino) rather than "no dampers" (sordini) - this remark suggests that the moderator would commonly be expected in such a mocement otherwise. Beethoven's una corda usage can be for short phrases, and he requests grading from one to three strings. He also differentiates between una corda and "piano dolce alle saite", third and beginning of fourth movements of opus 101 - it's not just quieter, but he wants the difference in tone color! If he writes it there, it must have been an accepted variation in practice at the time, part of the language. (Not in Rowland)
Schubert marks "con sordini" in the slow movement of D748 Piano Sonata in a minor, obviously not "with dampers" but "with moderator" , just to confuse the terminology issue. He also uses "verschiebung(shift) in the Trio of D845, Piano Sonata in a minor. Clementi makes no mention of the una corda, but Cramer interestingly uses it for "Piano, Diminuendo and Pianissimo", for grading as well as block dynamic shifts. He also says "As this pedal is only used in soft passages it does not require any particular mark." - so of it is mot marked, expect it to be used! But Field used una corda rarely.
Kalkbrunner and Thalburg appear to have recommended the shift pedal extensively in their manuals, but by then the "una corda" was not to one string but to two. Chopin didn't appear to teach the use of the una corda, but used it as a tone color, not a dynamic reducer, quiter frequently. All those lovely drifting-off codas in the Nocturnes and Mazurkas!".