Originally Posted by: jgraigWhy on a song like Smoke On The Water does the C dorian mode work?[/QUOTE]Because the song is in the key of G minor. The relative major is B-flat major & the 2nd mode of B-flat is C dorian. So, all those notes are part of the same home key.

B-flat major (ionian)
Bb-C-D-Eb-F-G-A

C dorian
C-D-Eb-F-G-A-Bb

D phrygian
D-Eb-F-G-A-Bb-C

E-flat lydian
Eb-F-G-A-Bb-C-D

F mixolydian
F-G-A-Bb-C-D-Eb

G aeolian (relative minor scale)
G-A-Bb-C-D-Eb-F

A locrian
A-Bb-C-D-Eb-F-G

Make sense?

In this case, it's just a matter of playing the notes of G minor in a different location on the guitar. At that point in the solo, playing in that position makes it sound as if he is "rooted in C". So, it can be useful to also say he is in C dorian at that point. It doesn't mean Blackmore was necessarily thinking that when decided to play that lick.
[QUOTE=jgraig]Is it safe to play these combinations on any root based blues?

Most blues tunes are based on major scale harmonies with minor scale ornamentations (dominant 7th chords with minor & major pentatonics). This tune is based on a minor scale rock sound with bluesy type riffs & licks. So, it's not exactly the same thing. However, the larger answer is that you can play anything you like the sound of. Then, use your knowledge of theory (scales, modes, chords) to understand what works & doesn't for your purposes.

These tutorials explain the modes; how to practice, understand & use them.

http://www.guitartricks.com/tutorial.php?input=370
http://www.guitartricks.com/tutorial.php?input=770

These tutorials cover how to play blues licks in pentatonic positions using major scale notes.

http://www.guitartricks.com/tutorial.php?input=217
http://www.guitartricks.com/tutorial.php?input=232
http://www.guitartricks.com/tutorial.php?input=826
http://www.guitartricks.com/tutorial.php?input=244

Finally, this tutorial covers his style:

http://www.guitartricks.com/tutorial.php?input=1473

Hope this helps!