E6000 is a very strong adhesive that is commonly used for attaching rhinestones and sew on crystals. It has a strong but flexible bond and is water resistant (once fully dried). 

Usage for attaching sew on crystals: 

1. Put a large blob of glue on the back of the sew on crystal. 
2. Place the crystal onto the leotard (be carefull not glueing the back and front of the leotard together. A sheet of parchement paper inside the leotard will prevent this.)
3. The glue should flow out from underneath the crystal just a little bit. This secures the crystal and prevents it from falling off. 
4. Didn't use enough glue? No problem: just lift the crystal and put a little bit more glue on the back of the crystal and stick it back on the leotard. 
5. Too much glue? Quickly get a q-tip or a tissue and remove the glue. Please be aware that removing E6000 is quite difficult even when it's still wet. 
6. Let dry for at least 24 hours before usage. The glue will cure best when your leotard is lying on a flat surface. 
7. After 24 hours the glue hsa cured and your leotard is ready to be worn!