Clean all glasses and vases you are painting on with white vinegar and a paper towel to remove any fingerprints, dirt or oily sticker residue on the glass. Ensure vases are not too tall to fit into your oven.
Draw the pattern you want to paint on the glasses and vases on paper using a marker. Place the paper on the inside of the glasses/vases with the design pressed against the inside of the vase. If you only want to color the glass, without creating a design, then a paper design is not necessary.
Paint the design or colors you want onto the outside of the glass using a fine paintbrush and bake-on glass paint. Wash the brush in hot water in between colors.
Dip a section of paper towel in hot water if you make a mistake and use it to remove the glass paint in the desired location. Leave the painted glass items to dry for 24 hours.
Set the glasses or vases on an oven tray and place the tray into the over before turning the oven on.
Read the glass paint instructions for the appropriate oven temperature and baking times, then set the oven to the right temperature and bake the glasses and vases for the recommended time.
Turn the oven off after the baking time has passed and leave the glasses and vases in the oven to cool down with the oven. Wash the glasses and vases in warm, soapy water once cold and leave to dry before using.