c. 1750—Italy

Circle Francesco Zuccarelli 1702–1788, Study of Angel Gabriel Blowing a Horn (see below; public domain).

c. 1750, a hornist in Dresden, Germany developed techniques for hand stopping that allowed for chromatic playing of the horn in the lower register, and this soon became a standard practice for horn players. 

Mid-1700s—solo pieces for alto trombone were written by Christoph Wagenseil, Johann Albrechtsberger, Michael Haydn, and Leopold Mozart.