Hellllloooo! This is one of the coolest ideas I've seen in a long time. In related news, it looks like I better plan a trip to the thrift store STAT (you know... for some glassware I can experiment on just in case something goes horribly wrong)!
As you know, I love any and all DIY projects that make use of thrifted glassware (hello, mod dot drinking glasses!). This is a really fun idea you can apply not only to tumblers but any kind of glass dish -- bowls and vases would look awesome, too! So, hit up your favorite thrift store and let's make some pretty glasses!