Jim Flick,Golf Digest Teaching Professional,
schreibt in Golf Digest, May, 2008
 

Get out of sand easy
 
To use the club’s bounce, open the face more.
ENHANCE THE BOUNCE: AS YOU ADDRESS A SAND SHOT, VISUALIZE THE FLANGE OF THE CLUB UNDER THE FACE.

 
OPEN POLICY:
To use the club’s bounce in soft sand, exaggerate opening the clubface. Swing down and through.

Photos By Dom Furore May 2008
 
As I’ve watched great bunker players over the years, namely Julius Boros and Sam Snead, I’ve noticed they play sand shots with a very open clubface. This exposes the club’s bounce to keep it from digging.
 
My colleague Rick Smith once designed a sand wedge made of Plexiglass. You could see the sole through the club so you were aware of how opening the face brought the flange’s trailing edge into play.
 
When executing a greenside bunker shot, many golfers are afraid to open the face. They think this will cause the shot to go to the right. Not true. Remember, the ball goes the direction the sand goes, which is along your swing path, regardless of where the face is aimed.
 

The more you open the face, the more bounce the club has. Now you can hit down into the sand behind the ball without fear that the club will dig. You have more margin for error. The softer the sand, the more you need to open the face. In hard-packed sand, open the face only a little, but lean your weight more to the left.