The tin scope is a shortwave (254 nm) UV light that is used to determine the tin side of float glass. This is an important step in order to achieve consistent fusing results. During the float glass manufacturing process, an invisible film of tin is deposited on one side of the glass sheet. To operate, just place the tin scope against the float glass at a 45 degree angle. The tin side of the float glass will produce a foggy or hazy appearance. Be sure to turn the light away from your eyes and wear protective UV spectacles when operating the tin scope.