Mozart's variation sets for keyboard are often used to fill out programs or recordings of other Mozart works; the 77 minutes of solid variations here are unusual. Mozart's variations aren't, truth be told, among his most fascinating works. The form plays to neither of Mozart's greatest strengths: his sheer capacity for great tunes (he wrote only one, or perhaps none, of the themes of these sets), and the sophistication of his formal thinking. So this collection of six Mozart variation sets is more for the hardcore Mozart enthusiast than for the general fan. That said, Dutch fortepianist Ronald Brautigam offers skillful performances of these fairly obscure works. All are fairly substantial sets, with between eight and twelve variations apiece, but they vary considerably in mood and in level of technical demand. Mozart wrote some of them for his students, and others for himself. Some of the latter group may have roots in extemporaneous variations Mozart performed at the keyboard. The most ambitious of the lot, a set of Ten Variations on "Unser dummer Pöbel meint," by Christoph Willibald von Gluck, K. 455 from a little-known singspiel, met with Gluck's delighted approval. Early on in the set, Mozart atomizes the theme to an unusual degree, and also moves off into a minor key fairly early on. Another highlight is the opening 12 variations in C major on "Ah, vous dirai-je, Maman," K. 265, using the tune better known in English-speaking countries as "Twinkle, Twinkle, little star." Brautigam's fortepiano is a modern replica of a 1785 instrument from Vienna -- spot-on temporally for this music. It has a very harpsichord-like sound when struck with normal force but fills out nicely under greater power, and Brautigam exploits its dynamic range subtly but fully. As usual with the Dutch label Globe's historical-instrument releases, the sound is clearly and unobtrusively recorded. This disc is recommended for libraries and for listeners with large Mozart collections.