Army Painter Mixing Balls
From the manufacturer:
Heavy pigment, old paint or a combination thereof: the Mixing Balls will make your paints perfect again. The 5.5mm stainless steel high-grade Mixing Balls will blend medium and pigment perfectly together, with a few shakes of your paint bottle.
Perfect For Warpaints Bottle!
5.5 mm Diameter Stainless Steel
100 Mixing Balls!