Jewelry Glossary - U

• Ultralap
  A plastic lap embedded with abrasive or polishing agents.
  
• Ultrasonic Cleaners
  Machines filled with cleaning solution which vibrate at high frequencies.
  
• Ultrasonic Drill
  A high-tech, fast-vibrating drill with electronically supplied abrasives.
  
• Undercut
  The property of some fibrous or granular gems to develop small pits during sanding and/or polishing.
  
• Uniaxial
  Stones with one optic axis.