George M. Lawrence provides scholarly examination of the plates.
George M. Lawrence, Report of a Physical Study of the Kinderhook Plate Number 5 (Princeton, N.J: n.p., 1966), 2–3.
The plate is about 2-7/8" high, weighs 17.65 grams and has an area of 28 sq. cm. The diameter of the hole in the top is 0.126" and is round within 0.001". The metal around the hole bulges, suggesting that the hole was punched. . . . The metal of the plate is fine grained and homogeneous as are modern metals. It has no spring when flexed, line annealed copper. Except for scratches, the surface is smooth as if the plate had been rolled or ground rather than hammered or cast. There is no evidence of corrosion except for the nickel-sized etch blotch on the "reverse" side. . . . I conclude from local flatness, the small thickness variation, the basic surface smoothness, and the taper, that the plate was cut from sheet which had been rolled, probably in a direction perpendicular to the length of the plate. . . . The plate is neither pure copper nor ordinary brass. It may be a low zinc brass or a bronze. The dimensions, tolerances, composition and workmanship are consistent with the facilities of an 1843 blacksmith shop and with the fraud stories of the original participants. The characteristics of the inscription grooves can be reproduced in great detail using the simple acid-wax technique, contrary to the judgement of the engravers.