That looks like a contemporary take on a slightly older design they had, (or perhaps it's a design that is still going). The shape is certainly newer than the design.
This design has been seen with paper labels, quite often two paper labels, one with a handwritten set of numbers, but nobody knows what the numbers mean.
Earlier pieces in this design have much smaller deep purple splodges to create the black background. The silver salts are often "painted on" in a straightish line around the middle, with big loopy bits.
It's one I like, I have a few pieces, but in earlier shapes.
This is not a Michael Harris design, sadly, I don't know whose it is.