Black Patina Research Articles

The statue of Karomama, a testimony of the skill of Egyptian metallurgists in polychrome bronze statuary

The statue of Karomama, Divine Adoratress of Amon during the XXII° Dynasty, is one of the masterpieces of the Department of Egyptian Antiquities, Louvre Museum. It has been recently restored, for the first time since the restoration by Alfred André done in 1896. That operation led to a description of the circumstances of the former restoration. It allowed to better understanding, through the detailed examination of the decoration, the techniques of polychromy on bronze pieces of art, as they were practiced by Egyptian metallurgist craftsmen. A comprehensive laboratory characterization of the different parts of the statue has been performed: X-ray radiography to evidence the mode of casting of the statue itself, of the assembled parts as the arms and the wig and of the base; analyses by non-destructive ion beam techniques on the particle accelerator AGLAE of the various inlays present on the statue and on the base. The results show an impressive juxtaposition of various metal alloys (gold, gold–silver and gold–copper) used to obtain a polychrome effect. The detailed examination and the analyses have evidenced for the first time the presence of an intentional patina on the inlays present in the wing quills of the statue and on the inlaid hieroglyphs of the base. This black patina, referred in the Egyptian texts as Hmty-km, was in general observed as a background on the Egyptian objects but is here reported for the first time on inlays. It is moreover demonstrated that several copper–gold alloys and perhaps several recipes are used to obtain a blackish coloration on various copper–gold alloys. Those observations are discussed in view of the existing literature about “black bronzes” or “black copper”.

San Francisco Monastery, Quito, Equador: characterisation of building materials, damage assessment and conservation considerations

Founded in 1535, the Monastery of San Francisco in Quito is one of the oldest monastic complexes in South America. Due to the large scale of the monument, this work is limited to the principal church and the first cloister, which are the oldest ones and most frequently visited. Samples were taken from the adobe, brick and stone structures and mortar joints and analysed by X-ray diffraction, optical microscopy, mercury intrusion porosimetry, calcimetry and scanning electron microscopy. The building materials were characterised, their decay mechanisms were studied and conservation strategies were proposed. Adobe samples exhibit the most severe weathering, while bricks and mortars suffer from water percolation and past conservation treatments, correspondingly. The andesitic façade is covered by a dark, red to black patina, consisting mainly of gypsum and apatite. Cleaning with dilute acid or laser cleaning would be effective techniques for the stone façade. In the case of adobe bricks though, consolidation treatment is more difficult to be executed, since they are usually painted.

ChemInform Abstract: The Formation of Black Patina on Copper in Humid Air Containing Traces of SO2.

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The Formation of Black Patina on Copper in Humid Air Containing Traces of SO 2

The formation of a black patina on copper in humid air containing traces of was investigated using on‐line analysis of and corrosion product characterization (x‐ray photoelectron spectroscopy, Fourier transform infrared absorption spectroscopy, x‐ray diffraction, and quantitative analysis of sulfite). In humid air (>75% RH) with 4 to 69 ppb , a dull black cuprite patina (200 to 300 nm thick) formed after 20 h exposure. However, when concentrations of were higher, copper remained shiny, as did samples exposed at low humidity. Sulfate was the dominant sulfur species on shiny as well as on black samples. At high concentrations copper is suggested to be passivated by a layer of chemisorbed sulfite on the thin air‐formed oxide film, while at low concentrations the film breaks down. Corrosion mechanisms are suggested for this active/passive transition on the copper surface. The formation of cuprite on the black samples resulted in a high corrosion rate, and an inverse correlation between concentration and corrosion was found. These results are in agreement with field studies on outdoor copper and bronze where the formation of a black cuprite patina and a high corrosion rate is observed in environments with low levels of .

Krustenbildung, ein schützender und zerstörender Vorgang: eine Fallstudie am "Reials Col.legis" (16. Jahrhundert, Katalanien, Spanien) / Patination as a Constructive and Destructive Process: The Case of "Reials Col.legis" (16th Century, Catalonia, Spain).

Abstract The "Reials Col.legis de Sant Jaume i Sant Maties" (Tortosa, Catalonia) is one of the masteφieces of the Renaissance style and was built in the 16th century with dolostones and calcarenites relatively well preserved and which are coated by an orange to black continuous patina. By studying samples obtained from different rock substrate and orientations the building stones and the layers forming the patina have been characterized by using several techniques (XRD, SEM/EDS, optical microscopy). The data obtained allowed us to establish a common sequence for this patina which consists of two layers: one micritic and one gypsum-rich layer in which, occasionally, there is bioactivity present living in and on the patina and the underlying rock. An hypothesis of the development of the layers of the patina is proposed on the basis of their mineralogical and petrographical features.

CONSERVATION OF THE ‘PILAR DE LOS ALAMOS’ MONUMENT

The 'Pilar de, los Alamos', which is typical of the Andalusian Renaissance style, is one of the most characteristic monuments in Alcala la Real (Jaen, Spain). It ,was built in 1531 by the architect, sculptor and painter Jacopo Florentin, who was a companion of Michelangelo Buonarroti in their youth. Diego de SHoe designed its use as a fountain in 1552 [1]. After a severe deterioration over the last century. became apparent, as observed from old photographic documentation and by a study of the current state of preservation, it was necessary to per. form an urgent treatment which, offering a maximum of safety, would allow the restoration of the original state of the bioclastic calcarenite. Environmental conditions had affected this limestone of high porosity (17-27%) and low hardness, scarcely superior to that of travertine [2], as discerned after performing thin-sections, X-ray analyses and SEM-EDX microanalysis. Three X-ray diffractographs' have shown the existence of epsomite (MgS047H20), gypsum (CaS042H20), natron (Na2C0310H20) and halite (NaCI), present in samples of the crust, concretion and efflorescence of soluble·salts on the stone surfaces. After measuring the pH the following values were obtained: 6.05 in the jet, 6.81 in the pool and 7.63 on the gray crust. A study of the climate and the biological agents was also accomplished. The organisms present include bacteria, fungi, cyanobacteria, algae, bryophytes and vascular plants of the families'l:rasulaceae, Resedaceae, Compositae, Brasicaceae and Scrophulariaceae. The state of preservation is the result of the action of physical, chemical and biological agents [3] ~Rain, wind, sunlight, crystalline microfracture, differential thermal expansion, adsorption pressure and, gelifraction are the physical agents. The main chemiCal agents are the comp9nents of airborne poliution: S02' S03' N02 and C12, which convert to strong acids producing a great dissolution of the stone and precipitation of sal~s [4]. The deterioration of this relief was characterized mainly by the presence of a sulphated crust, 'saline 'efflorescences, mortar disaggregation, pollution concretions, alveolization, a black patina of carbonaceous particles and biological colonization. Previous treatments were studied to discriminate completely the alteration morphology. The conservation treatment was carried, out in collaboration with the Escuela Taller for heritage restoration' in Alcala la Real

コバルト塩水溶液噴霧による溶融Zn-Al系合金めっき鋼板の黒変化抑制機構

コバルト塩水溶液噴霧による溶融Zn-Al系合金めっき鋼板の黒変化抑制機構

The technical examination of bidri ware

Bidri vessels have been manufactured in India from at least the seventeenth century until the present day and are known to be made of a zinc alloy, decorated with inlays of silver, brass or, occasionally, gold. The inlays contrast strikingly with the matt black patina of the vessel. It is this patina, easily damaged by standard cleaning techniques used on the silver inlays, which prompted the investigation. A number of vessels were analyzed and all were found to be alloys of zinc with between 2% and 10% copper (i.e. falling within the f:+11 phase field of the binary copper-zinc equilibrium diagram). Some have lead, tin or iron also present in the alloy. The compound or compounds forming the patina have not been identified. However, XRF analysis and replication experiments have proved that the copper content of the alloy is critical for the patina formation. The black patina forms instantaneously on immersion of the alloy in a warm solution of potassium nitrate (one part) and ammonium chloride (four parts). Standard brasses, as used for the inlay, are unaffected by the solution which induces only a whitish-grey patina on pure zinc. The ammonium chloride preferentially dissolves the zinc from the bidri alloy. The rest of the process is unproven but it is suggested that the resulting copper-enriched surface is oxidized by potassium nitrate.

Zn-Al系合金溶融めつき鋼板の黒変皮膜

Zn-Al系合金溶融めつき鋼板の黒変皮膜

Desert varnish as an age indicator for Aboriginal rock engravings: a review of problems and prospects

ments. In presently more arid areas, some rock surfaces display a dark reddish-brown to black patina or varnish, which may have a dull or or shiny appearance. The colour of the varnish is due to the presence of iron and manganese oxides; varnish may be manganese-rich (black) or iron-rich (reddish), but whichever oxide is dominant, both are usually present in the varnish. Various attempts have been made to establish either relative or ab-

A Portrait of Tiberius

The bronze head of the Emperor Tiberius, here reproduced (pl. vl) from new photographs, was found in 1759 near Mahon, in the island of Minorca. The exact spot is not recorded; but as the Duc de Crillon damaged the megalithic buildings at Trapuco, two kilometers from Mahon, while erecting a defensive wall round his guns, that may have been the finding-place. The head was acquired by the Marquis de Lannion, the Governor of the island; after his death it was bought by the Comte de Caylus, who gave it to the French king. It is now in the Cabinet des Médailles of the Bibliothèque Nationale.The bronze is covered with a black patina, and is well preserved. The eyes are made of sheet-silver. The head is life-size, 38 cms. high.