It’s sometimes hard at first glance to tell what a button is made of. For instance, one might wonder if this is Section 6 black glass or a Section 7 watch crystal (clear & colored glass). Let’s examine the button. If applied directly on a button surface, the rough texture of paint is typically visible. This button’s surface is totally smooth and the paint appears to be under clear glass, thus this button is a watch crystal. It is not black glass. See the back and the pitch in the image at bottom.