Raman investigation of artificial patinas on recent bronze – Part I: climatic chamber exposure

Abstract

In humid air, copper and its high copper alloys (bronze) tend to form an oxide layer (patina). Natural patinas protect copper and its alloys from further corrosion processes. On the other hand, artists have frequently deliberately patinated bronze for visual effects. Thus, it is of great importance to study the patina changing mechanism to follow its chemical changes and to predict in advance the likely corrosion processes. Green chloride and green nitrate patinas, applied over the brown artist's patina, were tested, and also brown patina and the patina that develops on bare bronze. The Raman spectra were studied after chemical patination, and after exposing the patina samples in a climatic chamber, which can produce an environment that resembles an industrial atmosphere, for 12 weeks. The structures of the patinas and of the corrosion products were characterized by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. Cuprite and cuprous sulfite were found on the brown patina, atacamite on the green chloride patina, and a mixture of gerhardite and rouaite on the blue to green nitrate type patina. After 12 weeks of exposure to humidity, a controlled concentration of SO 2 , and salt spray mist, the corrosion products changed. In general, clinoatacamite and paratacamite are the end corrosion products, after an intermediate brochantite stage on the green chloride and green nitrate type patinas. The end products of each patina type are given.

Decorated plasterwork in the Alhambra investigated by Raman spectroscopy: comparative field and laboratory study

“…However, in the absence of Ni, Zn or Co cations, the mineral phase more likely to form is clinoatacamite rather than paratacamite. In fact, the Raman spectral features recorded in the samples from the Hall of the Kings with three characteristic bands at 3440, 3348 and 3309 cm −1 together with those at 142, 362, 511, 897, 933 and 967 cm −1 are strongly coincident with those reported for clinoatacamite . Clinoatacamite was probably formed as a result of the degradation of the original azurite pigment in the presence of chloride.…”

Raman investigation of artificial patinas on recent bronze protected by different azole type inhibitors in an outdoor environment

“…(c)], respectively, can also be found. The bands of atacamite appear at 3438, 3350, 980, 970, 910, 816, 678, 514, 441, 417, and 355 cm −1 , whereas modes of gerhardite (Cu 2 (OH) 3 NO 3 ) can be found at 3550, 3472, 1324, 1049, 815, 713, 507, 475, 456, 416, and 259 cm −1 .…”

“…(d)], only the bands arising from the patina could be noticed. The broader band, with several maxima in the region between 350 and 700 cm −1 , suggests the presence of Cu and Sn oxides, whereas the well‐defined bands at 218 and 146 cm −1 suggest the presence of cuprite . The weak band at 289 cm −1 could also indicate the presence of Cu 2 S …”

Copper and copper patina

“…Niektoré tími použili aj doplnkovú techniku na odlíšenie minerálov vytvorených na bronze v rôznych prostrediach [86]. Len málo štúdií uvádza Ramanovú spektroskópiu ako jedinú techniku pre charakterizáciu rôznych koróznych produktov na bronze [21,24,[86][87][88][89][90]. De la Roja et al študoval rozdielne zelené patiny, ktoré boli vytvorené na medi a jej zliatinách pomocou zelených pigmentov, tak zvanej medenky [87].…”

“…De la Roja et al študoval rozdielne zelené patiny, ktoré boli vytvorené na medi a jej zliatinách pomocou zelených pigmentov, tak zvanej medenky [87]. Existujú rôzne dáta z Ramanovej spektroskopie chloridov a minerálov medi [88,89] a Ramanove spektrá niektorých bežných fáz skorodovanej medi [90]. Ale je pomerne málo štúdií o Ramanových spektrách týkajúcich sa rôznych patín na medi a jej zliatinách [21,24].…”