HAZARDOUS PHYSICS DEMO:open flame, sharp edges (SHOW MORE) Beer bottle in a microwave oven. IT MELTS. Blow-torch is required, goggles required, gloves NOT required (but don't touch white hot melted glass.) This demo is for teens and up, same hazards as for power tools. Blow torches and sharp broken glass: not for little kids!
Yes, you can safely touch these beer bottles, usually. Microwaves won't heat glass unless it's already melting. Because of boiled water and plasma, that one beer bottle was slightly too warm to comfortably grab with fingers. Notice that the melted wine glass at 3:40 could be touched just fine, even though the top was glowing white hot.
Does it harm the oven? Well, that's my original "garage test" oven from 1994 "Unwise Experiments" website, it's still working fine (but with paint a bit burned.) Whenever you see charred spots in your oven ceiling, you know that someone's been making plasma balls again. Very old pre-1970s ovens may have fragile magnetron tubes which won't tolerate an empty oven chamber. Best is to buy a "basement experimentation" oven for $10 at a garage sale.