The third prototype is a late-eighteenth- or early-nineteenth-century unmarked bass clarinet (I-Firenze, 109) similar in body shape to the bass clarinet in Sonogno. It is in four sections: mouthpiece with a small socket, brass crook, cylindrical body stained brown with a wing joint attached, and straight brass bell. It is probably in C because of its overall length of 107.3 cm. There are six keys with square key heads mounted in brass saddles and a wooden ring: S, A, f/c, A/E, F/C, and E/B.²⁴ This instrument is more advanced than the prototype bass clarinets and equivalent to a contemporary five-key soprano clarinet. The six finger holes are placed vertically on the wing joint, a seventh finger hole for F/C is on the right side of the wing joint adjacent to the A/E touch, and a ring for a strap is on the back of the cylindrical body.²⁵ The mouthpiece construction is very similar to some eighteenth- and early-nineteenth-century clarinet d’amour mouthpieces, and its brass bell is like those used on basset horns. Because it is the only six-key bass clarinet extant in this shape, it seems doubtful that it was a successful playing instrument. Van der Meer suggests a plausible date around 1780, although the construction characteristics suggest 1790 to 1810.²⁶

Footnotes
²⁴. See the detailed drawing and measurements in Gai, Gli strumenti musicali della corte Medicea, 221–222, and the brief description and photo in Antichi strumenti: dalla raccolta dei Medici e dei Lorena alla formazione del Museo del Conservatorio di Firenze, 103, 114.
²⁵. The finger holes are clearly seen in the photos of this instrument in Kalina, “The structural development of the bass clarinet,” 13, fig. 4.
²⁶. Van der Meer, “Vivaldi’s esoteric instruments,” 138. Young questions the authenticity of these three prototype bass clarinets. See Young, The look of music, 197.

Rice, From the clarinet d’amour to the contra bass, 253.