Alcoa spectrochemical standards are intended primarily for use in methods employing point-to-plane spark excitation and chill-cast sample disks as described in certain ASTM procedures. Because of the effects of macro and micro segregation and structure on spectral response in these methods, metal in any other form (ingot, sheet, extrusion, castings, etc.) should be remelted and cast in disk form prior to analysis. Some exceptions to this rule may be made in determining minor impurities or in any analysis where errors arising from structural or segregation effects can be tolerated. Alcoa recognizes that the compositional uniformity and accuracy of certification may make these standards useful in the calibration and control of other analytical methods including classical wet chemical approaches, inductively coupled plasma, X-ray fluorescence spectrometry, etc. To support these methods, all standards included in the catalog are available as lathe turnings in 100 gram bottles. Regardless of the methods employed, it is recommended that the zone lying within a 12 mm radius of the center of the specimen be avoided because of the slight segregation that occurs (rather rarely) in that zone.