As promised, I replicated the DIY Martha Stewart project : Beautiful Bottles. I used a collection of blue glass Ball jars from my Grandma's collection... she had hundreds - all shapes and sizes.
#1 : Clean jars thoroughly. Any dirt spots will be magnified when the enamel is applied.
#2 : Pour white enamel into jars. For clear glass, you can use a tinted enamel to make a colored jar to match your palette.