Nov_Dec_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 0 2 8 gate, saw turquoise corrosion at the top and a black waxy film towards the bot- tom. XRF registered levels close to Mo- nel, but with a few strange anomalies. Iron was elevated at 4.2% on the tur- quoise part of the grille, while sulfur also was 2.7-3.7%. Both acetone and naphtha raised iron further, suggest- ing a potential ferric patination com- pound, but the presence of aluminum may indicate aberrations with the de- vice or environmental contamination. Ferric chloride is known to be part of a green patination recipe for cast bronze, with a mixture of either copper nitrate, zinc nitrate, and hydrogen peroxide, or copper sulfate and water, both for gray brown or black brown bronze [6] . Initial XRD investigation was inconclu- sive, but Raman spectroscopy revealed antlerite, which was then discovered as a minor phase in XRD alongside a major retgersite phase with minor bunsenite. Retgersite, a hydrated nickel sulfate, is emerald green in color and was first discussed by Vernon in the 1920s. Ver- non described the formation in nickel of nickel sulfate NiSO 4 0.26H 2 SO 4 that sub- sequently turns into a basic nickel sul- fate NiSO 4 0.33Ni(OH) 2 that cannot be removed without abrasion [3] . The nota- ble absence of cuprite and rare natural antlerite formation in temperate climes reinforced the patination theory [7,8] . Investigation of the exterior sur- faces included the railing in the tower of Glencairn on the ninth floor, which had entirely different coloring. While large- ly brown, the decorative scrolls, joints, and weldings showed a clear outbreak of black and yellow green mottled cor- rosion product. Firmly encrusted, the black was raised from the now yellowed surface and was most noticeable next to hammered tenon joints through the balustrade, which was entirely matte gray with no corrosion whatsoever. The majority of brown areas, along with the tenon joint, registered Monel. The yel- low and black area, however, registered 49% nickel and 41% copper, with sol- vents raising the copper reading as high as 54% and sulfur from 2.3% to 3.8%. XRD for these areas revealed over 30% brochantite, 15% bunsenite, and slight- ly less cuprite. Organic analysis revealed bees- wax on the interior grille. As with Hill, it may have kept the formation of the tur- quoise corrosion product at bay. XRD’s Fig. 3 — Visual and technical identification of the James N. Hill gate at Woodlawn cemetery.