Glass and metal are two hard, non-porous surfaces that sometimes need to be adhered. Because glue does not easily stick to either surface, it is important to use a special adhesive that will strongly adhere the two items at the surface level. You also need to use a clear drying glue; glass is transparent, and using a glue that does not dry clear will leave you with an unattractive finish. One more factor to consider is the effect the glue has on the metal, because you want to create a strong adhesion without damaging the metal surface.
Gently scrub the metal surface to be glued with a piece of fine-grain steel wool.
Moisten the edge of a cloth with water, and wipe over both surfaces to remove any loose dirt.
Dry both surfaces with a clean cloth.
Apply a small amount of heavy duty clear-drying adhesive to one surface.
Spread the glue with a cotton swab to create a thin, even layer of glue.
Press the glass and metal surfaces together, and hold for 30 seconds.
Place a clamp, heavy book or similar item over the two surfaces to keep the metal and plastic tightly pressed together, and allow to sit overnight or until the glue has fully dried.