This particular shape is not shown, but in Mark Hills new book on Caithness glass, p 53 there is a pic of a design 4103 vase in clear colour cased in amethyst 6.5 inches tall. This is from the Glenislea range designed by Colin Terris approx 1981.
quote < Glenislea comprised single colours in Heather, Peat or Moss, and those also cased in amethyst>>
Is yours in this size range?
This is the only mention I can find of a clear colour cased in Amethyst, and the date would fit with the label on yours, which is an 80's label.
hope this is a clue in the right direction