>>8692892You can get smooth results from 3D printers as well, and not all of the gems I have seen were done that way. Many of them were sculpted with clay, or made with foam and/or thermoplastics. But that is beside the point.
If your gem is transparent, then no matter what you use to adhere it to your clothing, it will show through. Any sort of glue will show through as a dark smudge as it will stain the fabric. That leaves physical fasteners, and they will obviously also show through. The OTHER option would be a magnet on the inside of your shirt and a metal backing to the gem, but again, that will be seen through the gem, or at the very least, make it much darker.
Also, if you do anything to permanently adhere the gem to your clothes, then it will be far more difficult to wash your costume.
Your options here are either live with the fasteners or whatever being seen through the gem, or make a less transparent gem.
