These are heavy 2 oz. glass jars with black lids. They are great for loosening up paints that have become stiff in the tube – just mix the paint with a small amount of Walnut Oil or Oil of Spike Lavender. These jars are also perfect for holding custom mixes of paint, and for covering paint on the palette overnight. Just use a Q-tip to rub the inside of the jar with a small amount of Oil of Clove, and it will keep the paint fresh for the next day.