My idea was to use a printed fabric for a mermaid's tail, embellishing it with fancy thread through a layer of batting and the interfacing. I am hoping that when the interfacing dissolves, the extra batting will "puff" out around the stitches, giving extra dimensions to the details.
My main concern is that the interfacing, being fairly thick, will not dissolve entirely. The background will be deep blues, and any white bits will distract.
I guess I should make some samples and see what this stuff will and will not do.