You're welcome
I was wondering if the polarity of the copper cups had something to do with this working. It looks like the polarity is such that the excess electrons are on the inside of the jar. As he carefully removes the inside cup, the electrons are trapped inside the jar by the electric field from the charge difference relative to the outside cup, amplified by the glass dielectric.
The polarity is not the key as we are not storing electrons like apples in a basket. The electrons are not stored in the jar but are on the surface of the glass.
I was wondering if the ordering of the action was the same and the polarity reversed, the charge would leave the glass with the outside cup as it is disassembled, the electrons are self repulsive and distribute to the outside, making the demo fail. He is showing he can have a jar of electrons.
I don't think so.
He must also be standing on an insulating mat.
He may be, but that is of little concern. One side of the glass has too many electrons and the other side of the glass has too few electrons. A completed circuit would let the charge imbalance try to equalize the two sides. It has very little to do with the floor.
The reason I say very little is that the charge separation across the glass can cause side effects. An illustration:
Positive Pete is standing on one side of a fence and Negative Norton is on the other. Due to prior events, Pete is covered with holes due a deficit of electrons. Norton is covered with an excess of electrons. The charge imbalance each has balances the other across the fence.
Wearing rubber boots, a neutral monkey named Balanced Barry approaches Pete and notices that electrons begin piling up on his face while his tail develops holes. Curious indeed.
Then Barry goes to the other side of the fence and approaches Norton and notices that holes appear on his face and electrons begin piling up on his tail. If Barry only knew he was being polarized, he might take caution with his tail.
Barry lets his tail touch the ground and some of the extra electrons on his tail begin to spill onto the ground. When Barry is right next to Norton, he picks up his tail. Barry now has a net positive charge. He begins the journey back to Pete's side of the fence and somewhere along the way lets his tail touch the ground and gets a static shock.
On the other side of the fence again, Barry approaches Pete and again notices that electrons begin piling up on his face while his tail develops holes. Barry lets his tail touch the ground and some electrons begin to leave the ground and disperse themselves somewhere along his frame. When Barry is right next to Pete, he picks up his tail. Barry now has a net negative charge. Now bored with the whole thing, Barry leaves the scene but lets his tail touch the ground and gets another static shock as the atoms in his body restore equilibrium. We suspect Barry does not thank Mother Earth for the charge donations.