You can use your stained glassware as a candleholder or even a vase, but keep in mind that if you don’t bake your glass long enough, then the color may not be waterproof (Mod Podge is water-based). To play it safe you can paint on the outside instead, just make sure to use the Mod Podge that has a glossy finish!
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DIY: cement star votives
color glass jars with mod podge and food coloring. Like this even better than the paint method...great jewel tones.