Your demonstration starts by showing both sides of the mirror.
A silk is shown to the audience and is used to clean the mirror.
As the magician is wiping the mirror the handkerchief begins to penetrate the center of the glass.
Halfway through, the mirror can be turned around and shown on both sides with the handkerchief sticking out.
The mirror is faced towards the audience once again and the silk is pulled through.
There are no visible holes.
The penetration takes place right before the eyes of the audience.
Both before and after the effect the audience sees a solid mirror, which the magician can tap to show how solid it is!