Tempered Windows Look Dirty To the Editor: Glass manufacturers are advertising their ability to produce large glass units with high insulation properties. I would like to share my unpleasant experience using this product in a design situation where the glass went down to the floor and required tempering (see specs below). I had 8x8-foot and 8x12-foot insulated glass units installed in a new house. After the installation, we cleaned the glass and found a cloudy color checkerboard pattern across all the glass. The supplier of the glass says this occurs in the tempering and is within industry acceptable tolerances. It doesn't sound right to me that the glass industry is spending all this money and the result is glass that looks like "dirty" windows. SPECS: