The G856BL is a 4 oz cobalt blue glass boston round bottle with 24-400 neck finish. The boston round bottle is distinctive in its classic shape. Characteristic of the boston round are its rounded shoulders and rounded base. Glass has high clarity, can be colored, has high chemical-resistance levels, and has extremely high resistance to heat and cold. It is great for storing essential oils. This container is cobalt blue, an electric and vivid blue. In the case of glass, cobalt blue is made by mixing cobalt oxide into the base glass. Plastics are colored by using pigments. This cobalt blue color provides some UV protection for light-sensitive products. This item has a 24-400 neck finish. The first number refers to the diameter (in mm), and the second refers to the closure depth, style and thread. This container can be paired with a closure with this matching finish (see Matching Items below).