At the end of Disney’s Tangled, spoiler alert for a 13-year-old movie, Flynn uses a large mirror shard to cut Rapunzel’s hair to a much, much shorter length, down to about a quarter of the way down her neck, and not entirely uniformly. He grabs it, bunches it, and slices.
In real life, could this have been accomplished?
Not seen the movie but yes it should be relatively straightforward.
Humans have flaked flint, quartz and other silicious (glassy) minerals to produce sharp edges for millions of years. Most of them are not necessarily elegantly used, but there are good records of indigenous people in the past couple of centuries using bottle and window glass for shaving and hair cutting and other delicate procedures. The main complication is that flat sheet or cylindrical glass tends to break squarish, when you need a very tapering profile.
Also, naturally occurring obsidian is a type of glass and is about 1.78 gazillion times sharper than regular glass. Modern obsidian scalpels are used in eye surgery because its much sharper than metal equivalents and as sharp as diamond scalpels.
actually, you can cut hair with a broken pop bottle …as I found out the hard way…I had long hair and wasn’t totally out of the car and my hair was in the way when the door closed and mom was already in the store … so my dumb ass brother broke a pop bottle and cut my hair with it …
Many years ago I tried to repurpose a large double pane picture window for a greenhouse. It was maybe 4’ x 8’ and was very heavy. We twisted it slightly while loading it on the truck and it shattered. One large chunk sheared the entire side off my shoe. It did not touch my foot. I still think about it every so often.
Glass can be honed to an incredibly sharp edge and can certainly occur that way as a result of breaking. I have a two inch scar on the back of my hand where broken glass cut cleanly through my skin and severed a tendon. I’m sure it would have cut hair.
If hair is pulled reasonably taut, it doesn’t take much sharpness to cut it, I think. Barbers use sharp instruments to avoid the pain caused when a dull blade pulls the hair, but it still would be cut.