vivaplex, 6, cobalt blue, 10 ml glass roll-on bottles with stainless steel roller balls - .5 ml dropper included vivaplex these high quality, cobalt blue glass roll-on bottles with stainless steel roller balls are perfect for use with essential oils, perfume oils, and other liquids. snap in the roller-ball by gently placing the roller-ball in the bottle and then firmly tighten the cap until the roller-ball snaps in. use the roll-on bottle to apply the perfect amount of product each time. remove the roller-ball by applying pressure with the cap. the beautiful, cobalt blue glass provides protection from potentially harmful light and the convenient size makes it perfect for travel.