Historically speaking, stained glass paint was made using dry glass powder mixed with a binding agent like water, sugar and sometimes vinegar. Today's stained glass paint is made with manufactured chemicals designed to paint on glass, after which a waterproofing layer is applied to seal the glass. Removing stained glass paint from windows is an easy process as long as your stained glass window has a flat surface and you are comfortable working with a razor.
Fill a gallon-sized bucket with water and place any type of household bar soap into the bucket with the water.
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Stir the water until it appears soapy. Soapy water helps the razor to glide easier when applied to glass.
Wet a cloth in the soapy water and wipe the stained glass until it is thoroughly wet.
Warm 1 cup of vinegar in the microwave for 45 seconds. Rub the vinegar using a second cloth over the section you are about to attack with your razor. This will help further soften the paint.
Place your razor at a 20-degree angle against the glass surface, pointing your edge in the direction you plan on scraping.
Push the razor blade into the paint and guide your razor toward the window's edge. The paint should peel off. If there are several layers of paint, it will peel off in layers. If there is just one layer, with any luck it will all come off at once.