Alloy Imperfection. A poor mixture of metal prior to being blanked and struck into coins or medals. These imperfections include occluded gas (forming gas pockets in the metal), layering of metal (causing FLAKING, LAMINATIONS, or split planchets), dirt or impurities lodged in the alloy (causing BLISTERS or IMPRESSED ERROR pieces), or other imperfect mixture of metal. Some surface alloy imperfections, as bosses or pitts, noticed after striking may be removed – by chasing – before a medallic item is finished; others may escape inspection and not be noticed until later.