story artefact: stones in the water

Here's an idea I like, but will probably never get around to using, so this is Creative Commons Share Alike. Use it freely if you want.

A lot of shops around coastal tourist spots sell these little souveniers that you may have seen. They're a clam, oyster or muscle shells that have been cleaned out of their original occupants. They're taped back together with a thin strip of paper. You drop it in a glass of water and the strip dissolves and the shell opens and a little flower made of paper and string floats up out of the shell.

In this story, an ancient Chinese (well, it doesn't need to be Chinese, any country that has been along to have ancient forgotten arts will do) craftsman made the most exquisite of these flowers, the most beautiful the world has ever seen. Only instead of making them out of shells, he disguised them as rocks. The rocks were completely convincing. There was no way to tell by looking at them that they were anything but rocks until they were dissolved in water, wherupon they would split

Today these rock sell for incredible prices, but the one thing that makes them valuable, the artwork inside them, can never be seen because actually dissolving them in water would destroy their value.