I used to get so tripped up trying to figure this out. (Don't get me wrong, I still run across things that make me have to second guess myself). But here are a few tips to help you know the difference between crystal and etched glass.
What is Crystal?
It is glass with lead added to it.
According to an article I found in the Chicago Tribune , Crystal is glass with 24% or higher lead added. Back in the day, the EU got together and said not only must the lead content be 24% or higher but it must also have a density in excess of 2.90 and a reflective index of 1.545 to be considered Crystal. The US apparently never created specifications and typically goes by the EU standards.
The article then goes to explain that Waterford Crystal has a lead content of approximately 32 percent.
But aren't we suppose to stay away from lead? So, I am not sure I would let Grayson drink out of lead crystal but for the for short period you would use to store it, it is okay to use to drink. Same for decanters. I would use it all to serve and pour....not to store items.
The Prism Test
Here is the best tip, in my opinion, to tell the difference. If you hold the item up to a light source, do you see a prism? Only Crystal will prism. Glass will not.
Below I took a flashlight and put it through crystal and glass so you can see the prism difference:
See that ROY-G-BIV'n up in there at the top of the image?
See how the glass doesn't rainbow and prism like that?
The reason it does that? Yep. The lead oxide makes it sparkle and prism.
Lead will usually be heavier than glass (because of the lead).
Tap the item with your fingernail. If you hear a musical type tune, it is crystal.
Glasses have thicker rims than crystal.
The cuts made on crystal will be more rounded than the ones made on say an edged glass.
UV light on crystal will make it look purple and blue.
Do you use crystal to entertain?