chromatic accordion was created in the 1850's by F. Walter,
when he rearranged the reeds of a Three Row Diatonic. It could
play a 46 note chromatic scale. The Chromatic Button Accordion
is not diatonic, and probably has the greatest range of treble
notes of any accordion available today. Their size ranges from
an accordion with 20 treble keys and 12 bass buttons, to the
modern Chromatic Button Accordions which have up to 6 rows of
treble buttons and 160 bass buttons.
The chromatic keyboard has more than one system. It can have
anywhere between three and six rows of small round (and sometimes
rectangular) keys. The fourth, fifth and sixth rows are repeats
of the first three rows, to increase fingering possibilities.
The two most common layouts are the B and C systems. The B system
is better for technically challenging works, whereas the C system
is easier to play chords and play melodic music. The six row
chromatic is used almost exclusively by Yugoslav players and
is also known as the Serbian accordion.
The bass system can be stradella, free bass or convertible between
the two, the free bass facility giving an overall range of up
to 11 octaves. This makes it possible to perform serious classical
or contemporary works.
The chromatic accordion is probably most widely used in Russia.
There it is called the Bayan, and the Piano Accordion is called
just the Accordion.