Use Disk Image to rescue an unmountable drive partition (OS X)

From MacOSX Hints

macosxhints - A possible way to save a corrupted drive or partition

An unhappy event happened to a cheese-maker friend -- he hadn't made any back-ups of his old G3 tower, and naturally the hard disk went down along with all the recipes of his award-winning cheeses. I tried all the usual -- TechTool, DiskWarrior, Disk Utility -- but they all just threw up their (figurative) hands in horror and simply gave up. (Disk Utility would see the disk, but not mount it).

In a fit of desparation, I told Disk Utility to make an image of the seen but un-mountable partitions. And quite surprisingly, it worked!