>Has anyone actually tried to make a blue (or purple) dye from a Murex or a Purpura in modern times? How would you do it?<

It depends on how much you want.  To get purple stains on your shirt, all you have to do is pick up any of the relevant species and let some of the drips get onto you (personal observation).  To get enough dye for an entire piece of cloth requires more effort and more snails.  The ancient Phoenecian approach was to crush the shells.  Simply annoying live shells into producing the dye and then letting them go is obviously ecologically friendlier, though probably more effort per yield.  Other purple-secreting mollusks would probably work, too, e.g. Janthina.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487-0345 USA
    [log in to unmask]

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa