The colachon is a special kind of lute developed as a bass line melody instrument. It has a much stronger and louder sound, is fully chromatic and gives the Basso continuo line in large halls, opera houses and churches the kind of impetus it needs to cut through and support the singers and higher instruments. There were Italian instruments, much smaller, used in the Comedia dell' arte. Our type here is found mostly in central European countries, Austria, Bohemia, Germany. It has a long scale. Chords can be played as well and depending on the tuning, it is very easy to transpose at sight into every key - a task almost impossible on a lute or guitar.
Johann Kuhnau, Bach predecessor in Leipzig asked for two colachon to be bought for both main churches. Telemann wrote a number of concertos for flutes and colachon. Johann Mattheson in Hamburg also asks for the colachon in orchestral music, since the lute, as nice as it may be in the chamber, just can't be heard in a larger setting.
As a Basso continuo player I'm always looking for new sounds and instruments that might have been lost along the way or escaped the standardization of the 'Baroque Orchestra' which pretty much reflects an ensemble typical for around 1730 - 1750. By then the Baroque was over. All the more interesting experimental settings are not on the screen of conductors, fixers, musicians or audiences.
I did quite a bit of research and asked Dieter Schossig to measure the Schorn instrument in Salzburg. He build the most wonderful instrument for me, which I like to use best in Salzburg music, like Biber's Mystery Sonatas, Muffats orchestra music or Telemann's concertos and cantatas. Still waiting to be asked for Bach and Handel.
An article of mine about the colachon was published in 2021. You find it further down.