Spiral tuning has the notes of the major scale alternating between the blow and draw notes. It provides draw bends and overblows from holes 1 to 10.
It also provides a lot of chords. You can add a major or minor seventh to many of the
chord triads shown here.
You can alter the tuning of a Standard Richter harmonica to Spiral Tuning.
Here is a visual aid to the modification:
Shown above are the offsets in semitones. You only need to lower the pitches. And you only need to modify 12 of the 20 reeds.
You can use solder. You can also use BluTak which is a very effective and stable way to lower the pitch of a reed by several semitones. It's the easiest method, too!
Second Position Spiral is another alternative where the tonic is the 2 draw.
The chords available are as follows:
Here are the modifications. You need to alter an extra reed:
