Here's some great suggestions and links share by people from the Crazy Quilt List ...
Velvet
Embossing
I've found embossing on velvet works best on rayon (or mostly rayon)
... the heat seems to "melt" the fiber and there's a better imprint. Cotton
velvet seems to resist the heat and I've not gotten as definite an impression.
Here are some links shared from the CQ List:
Fabric Dying
Definitions