Skill is definitely a prerequisite for any glass production. I've seen some molds that even in the same factory could only be made by a unique "shop" of men. Other molds have been moved from one factory to another and have proved to be too much of a challenge for one over another. LIkewise, the design of the molds is very important, not every mold shop is equal to others. Some molds if made wrong will not support decent production. I know, I own some =that I bought when some factories have closed. In addition, the person ion charge oif doing the batching and the melt is crucial. Making some of these phosphate and fluorine glasses can be difficult to me3lt for decent production.