Clean the glasses with mild detergent, rinse and rub them with a cloth dampened with rubbing alcohol to clean the surface further of any oil from your hands.
Sketch your design on paper first with colored pencils as a guide.
Use gloss acrylic indoor/outdoor enamel paints in multiple colors (available at craft supply stores or online) to apply your design to your glasses. If you don't like your design the first time, simply wash it off with a cloth dampened with rubbing alcohol and begin again.
Use flat or blunt end brushes for petals and leaves and fine point brushes for stems and fine detailed lines.
Dry your finished glasses for 48 hours.
Place the glasses carefully in a cool oven, making sure they are not touching each other.
Heat the oven slowly to 325 degrees and hold the temperature for 15 to 30 minutes, according to the instructions on your brand of enamel paint. Turn off the stove but do not open the door. Let the oven cool slowly to avoid cracking the glasses.
Rinse the finished glasses gently with cool water and the mild detergent. Allow to air dry.
Repeat the above step every time you wash your hand-painted glasses to maintain long lasting decorations.