... 3.high light transparency. colored borosilicate glass tubingUsuage:1.solar vacuum tube.2. lighting.3. glass blowing.4. glass arts&crafts.5.glassware ... healthy, contain no heavy metal.3.very hard.4.high light transparency.5.low C.O.E: 3.3 colored borosilicate ... glass tubing Features:1) Available colors: clear , dark blue, light blue, amber, light yellow, green, pink, purple, red and opaque black ,opaque ...