the surface of this kind of tube is smooth and the tube is colorless. the properties of the tube are: high purity(sio2>99.99%), abrasion resistance(any acid except hf acid ). fire resistance(softening point 1700 centigrade). low coefficient of thermal expansion(5.5x10-7/centigrade, heat the tube to around 1100 centigrade, then put it into ordinary temperature water, the tube won't crack, ); the surface can be done with gold plating. gently using sizes: single outer diameter x double outer diameter 8x17mm, 11x23mm, 15x33mm length 400-4000mm lianyungang granhtquartz factory