A basset-clarinet is an A-clarinet with an extension of a terts down. It is in fact related to the bassethorn in F of G. This instrument has been (almost?) exclusively used by Mozart for his famous clarinet concerto KV 622 and his clarinet quintet KV 452. Because Mozart's clarinet concerto is so important, the basset-clarinet is quite an interesting instrument in spite of its small applicability. For the concert the extension must be chromatic and the shape of the Viennese bassethorn is not suitable for this. It has long been unclear how this instrument might have looked.
In a library in Riga in 1992 programmes has been found of concerts which Anton Stadler (Mozarts favorite clarinettist) has played there in 1784. Two of those programmes show an engraving of Stadlers instrument (see image).
Following these engravings and existing instruments of the same model but not directly associated with Mozart and Vienna (for example of j.B.Eisenbrandt) I reconstructed the basset-clarinet with my Lotz A-klarinet as the starting point.