The easiest way to do this is to turn off the visibility of all the layers on the layer palette, so that only the two cutout layers are showing. Then turn the bottom layer back on. Now let's add our glass. Create a new layer and drag it down on the layer palette to just under the cutout layer we just completed. With the ellipse still selected, select the cutout filter once again.
Real glass has a highlight.
Any other tutorial that I found always had you airbrush in a highlight. Here's what I came up with to gives us a good looking highlight, that followed the contour of our glass. Plus it gives us a little extra sheen that really adds to the effect. Go to the layer palette and click the layer with the black cutouts that we merged earlier, to make that the active layer. With this technique, you can make a glassy button or add a frame to your image or whatever else your imagination can come up with.