That makes sense since a solid piece is much sturdier when compared to a bunch of pieces glued together.
After that, they are heat-set hence they retain their shape. However, the center of crystal jewelry, you cannot find a related certificate. https://www.pressadvantage.com/story/65432-contractors-state-license-center-leads-the-way-in-zoom-classes-for-contractor-licensing-in-los-angel