In the early 20th century, thousands of boys were employed in glass making industries. Glass making was a dangerous and tough job especially without the current technologies. The process of making glass includes intense heat to melt glass (3133 °F). When the boys are at work, they are exposed to this heat. This could cause eye trouble, lung ailments, heat exhaustion, cut, and burns. Since workers were paid by the piece, they had to work productively for hours without a break. Since furnaces had to be constantly burning, there were night shifts from 5:00 pm to 3:00 am. Many factory owners preferred boys under 16 years of age.