How do I remove a glaze from a window pane of stained glass?

by Alyse Carter
(Maryland, USA)

Q:I recently bought a window pane of stained glass at a local antiques store.

The colors on the window are fantastic, the only problem is the previous owner must have thought it was too colorful and covered parts of the window in a swirling motion of black glaze.

Some parts are more heavily coated than others. I've tried water, paint thinner, and a small razor. None have helped make a lot of leeway in getting rid of the glaze.

The piece looks rather old and I don't want to crack the glass.

Do you recommend any other methods of removing the glaze?