I'm not sure how well this would work with bottles, but what about using colored paint and swirling it around and then turning them upside down to dry so the excess paint drips out...
How to Paint Clear Glass Ornament Balls
Painted Ornaments
For small necked bottles, I'd get several eyedroppers or cut some drinking straws in half and use that to place the paint inside without smearing it so you can get the swirly effect nice and clean, but try it the regular way to see if it works with the bottles.
Using something like metallic gold or silver and dark purples, deep reds and the like should look really cool, they won't scratch off since the paint is all inside and you should be able to slide a rolled up scroll inside.
Or what about making the LABEL to be the invite info? That would be fun to write:
"TITLE of PARTY"
date time
Potion ingredients:
A small pinch of magic,
pointed hat and a broomstick
now we just need YOU
for the perfect brew!
Have a little oval aged paper label attached and have a little witch graphic, cauldron, or something as the center of the label, with the activities sort of circling the outsides. and the ingredent/address info on a backside label (so two labels, one front and one back, but would be a really cool invite)
