Mercury Glass. Mercury glass window curtain drapery medallion holdback tie back. Mercury glass medallion measures 3 1/4 inch in diameter; Base measures 1 7/8 inch in diameter.Projection from wall is 4 3/4 inch. Mounting hardware included. The drapery medallion holdbacks are great to use as a traditional holdback. You can also use them instead of a curtain rod to attach a curtain valance or curtain panel to the wall.