: I've seen a bit of Pyrex and none of it that I have seen has had any color to it. It's all waterwhite. As far as I know, tempering a piece of glass doesn't add any color to the glass. BTW, I just remembered that I saw a piece of tempered glass last weekend. Go grab a Polaroid sunglasses and the mirror (if the coating is off of it or you can otherwise see through it) and look at the glass through the Polaroid glasses with light from a windshield reflecting through the pyrex, light path is sun, windshield, pyrex, Polaroid and finally your eye. Rotate the Polaroid and you will see the image change. This is the quick and dirty test for Tempered glass. The image is very interesting. : Tempered glass needs to be annealed before grinding so consider that the local glass shop is going to heat it up for you. Thanx!