Loss of Glaze on Crown Lynn tableware

A couple of our stored Crown Lynn pieces have a loss of glaze shininess. I have hand washed them but still there is this dullness around the rim as if the something has caused the glaze to dull. What causes this, is it just a Crown Lynn thing, can you do anything about it? And do people want this stuff in this condition? I can't get any photo to show it up but it is noticeable to the eye.

Some patterns are put on top of the glaze and when they are put into dishwashers the results are dire, as the pattern is almost completely bleached out and they end up looking disgusting.
Another reason for 'dullness' is from use. Knives scratch into the glaze and the shininess goes dull from wear and tear. There is always a market for hard to find patterns. Just include the fact that they have been well used in the auction.