Everyone is wasting you time sir. Welding glass is a great was to view the eclipse. Do not go below Shade 11. I don't know how the absorption rate increases when stacked. You can buy 4 1/2" by 5 1/4" glass from Air Gas for $3.20. I am have Shade 12 mounted to my binoculars. Everyone else who is poking a hole in a box or black out curtains that is fine. But spend a few pennies and at lease get the paper shade glasses at 7-11 to see the real thing. This is near a once in a lifetime event don't just watch the reflection.