Describing accents

Today, I found myself describing someone's accent as being "like cut glass," because that's the expression that first came to mind when I heard her accent. Then I realized that I don't actually know what the expression means. I've heard it before, as applied to accents, but I couldn't tell you what kind of accent it was being applied to. It occurred to me today when hearing someone speak, but I have no idea whether or not my interpretation of the expression is the same as the common meaning. It's all very intangible. I don't even know what cut glass has to do with the particular accent (like the sound of cutting glass? like the appearance of cut glass? like the sound of cut glass stemware tinkling against each other?), and yet the simile came to mind unbidden. I know what "plummy" means in describing accents, but I have no idea what that actually has to do with plums.