Freckles are brown spots that show on the skin, especially on areas most confronted with the sun's rays. The face, chest and shoulders are most common locations where freckles develop. They are quite harmless but they can be be extremely unsightly should they give full attention to specific areas about the face, especially about the cheekbone as well as the nose area. This is particularly true with light-skinned people for the reason that brownish spots look like stains in an otherwise smooth and milky white skin. Brown-skinned or dark-skinned folks have it better since they have built-in protection with melatonin, as well as the realization they can readily hide their dark brown spots. When a mixture of different substances is rotated at extremely high speeds within a closed path (in your case a closed container), substances of higher mass often go on to the outermost path and lighter particles experience the nearest to rotating axis. The same principle can be used in centrifuge oil cleaning.