Tunings suitable for Celtic Harmonica

My explanations are for the key of G - other keys maintain the same patterns. I have picked this as a very popular key and because it gives more trouble than D.

RICHTER or BLUES HARP Standard 10 hole Diatonic - middle octave being holes 4 to 7
 
Blow G B D G B D G B D G
Hole 1 2 3 4 5 6 7 8 9 10
Draw A D F# A C E F# A C E

This is the commonest 10 hole harmonica, it was developed for playing melody in the middle octave and chords. The bottom octave repeats the D and misses 2 notes , C and E. You can play many tunes in the middle and upper octaves. There is also a Low D tuning that can be used in the upper section for some tunes and there are techniques good players use to partially overcome the missing notes. But this still leaves some great tunes mortals just can not play satisfactorily. The missing low E is the most problematic.

PADDY RICHTER - Brendan Power's solution is to change one of the repeated D's to E. He choose to raise the 3 blow. He has written an instruction book on using this tuning and sells these harmonicas.

Blow G B E G B D G B D G
Hole 1 2 3 4 5 6 7 8 9 10
Draw A D F# A C E F# A C E

This makes most of the tunes playable. Once mastered it leads to a very expressive sound and enables fast playing where required. The main problem for some people is it changes the suck/blow pattern in the low octave. This will be most noticeable for people who have played standard Richter tuning for years or button accordions. This tuning is available from Brendan and also from Seydel.
Brendan uses retuned Hohner special 20's and also the half-valved Suzuki Promaster. This is highly responsive and is what he uses on some of his CDs.

SOLO TUNED - The same layout as a chromatic with the slide out, it repeats the same pattern as the middle octave of a Richter

Blow G B D G G B D G G B
Hole 1 2 3 4 5 6 7 8 9 10
Draw A C E F# A C E F# A C

As standard harmonicas they are usually only in the key of C in 10 or 12 hole.  Seydel, Hohner, and Huang make them. Brendan Power and others supply customized  versions in other keys.

CHROMATICS - You can get them in all keys. Great for slow airs and tunes with accidentals. The sound is not to everyone's taste. They do require more air and if you are a wet player the wind savers may stick.
Seydel make them in C and G without wind savers.