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Components of what may be an ancient battery. Iraq, first
century CE. At left is the clay jar in which the iron rod (center)
and copper cylinder (right) would have been placed. The dark
fragments are bitumen, which would have been used to hold
the three components together.
Image courtesy of Department of Antiquities, Iraq.
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Pourbaix diagram
showing plot of
natural aqueous
environments with
characteristics in
different regions
of Eh and pH.
Image courtesy of Schweizer 1994 and David A. Scott .
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Pourbaix diagram showing distribution of natural aqueous
environments, which can be seen to cover a considerable
range of Eh and pH
conditions. The dotted
area represents the
major concentrationof many thousands
of Eh and pH
measurements, while
the surroundingirregular box
represents the
boundary for all
measurements.
Image courtesy of Baas Becking, Kaplan, and Moore 1960 and David A. Scott.
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Image courtesy of David A. Scott.
Agencya
Soil type Years Corrosion(m/year) Maximum pitting(mm/year x 104)
BNFMRA 5 least corrosive 10 0.5 - 2.5 Uniform: no pits
BNFMRA 4 least corrosive 5 5.0 - 25 0.040
NBS 9 least corrosive 14 4.0 - 2.5 0.043
NBS 2 next mostcorrosive
14 25 130 0.033
BNFMRA Acid clay/acid peat 10 53 66 0.046
BNFMRA 2nd series: b cinders 5 66 0.32
NBS 3 most corrosive:rifle peat/tidal marsh
14 160 355 0.115
Analysis of corrosion of soils
a BNFMRA = British Non-Ferrous Metals Research Association (now defunct); NBS = National Bureau of Standards.b 2nd series = second attempt to derive accurate results for this set of data.
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Image courtesy David A. Scott.
Name Formula Concentration (ppb)
Ozone O3 50 200
Hydrogen peroxide H2O2 10 -30
Nitrogen dioxide NO2 10 45
Nitric acid HNO3 1 10
Hydrogen sulphide H2S 0.1 0.5
Carbonyl sulphide COS 0.5 0.6
Sulphur dioxide SO2 5 24
Carbon dioxide CO2 (3 6 ) x 105
Formic acid HCOOH 0.2 1
Acetic acid CH3COOH 0.2 1
Oxalic acid (COOH)2 Not detected
Formaldehyde HCHO 4 15
Acetaldehyde CH3CHO 1 8
Hydrogen chloride HCl 0.5 - 2
Typical Modern Concentrations Atmospheric Gases
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Image courtesy of David A. Scott.
Conversion factors for concentrations of some pollutantgases in parts per billion (ppb) and microgram/m3 (g/m3)
Name Conversion Factor a
ppb to g/m3 g/m3 to ppb
Acetic acid 2.45 0.41
Formic acid 1.88 0.53
Acetaldehyde 1.80 0.56
Formaldehyde 1.23 0.82
Hydrogen sulphide 1.39 0.72
Carbonyl sulphide 2.45 0.41
Ammonia 0.70 1.44
Sulphur dioxide 2.62 0.38
Nitrogen dioxide 1.88 0.53
Ozone 1.96 0.51
a The general expression is microgram/m3 x conversion factor = ppb. All measurements are at standard temperatureand pressure, with temperature assumed to be 25C.
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Stability diagram of thesystem Cu-SO4-H2O with
fog and rain areas shown
for urban atmospheres.
Area A = atacamite
stability; area B =
brochantite stability.
Although the diagram
over-simplifies the actual
situation, it does showthat brochantite should
form in outdoor exposure
an that antlerite may
form in more acidicconditions. Image courtesy of Graedel 1987 and David A. Scott.
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Building SO2
(ppm)
O3
(ppm)
NOX
(ppb)
NO
(ppm)
Dates
National Gallery, London 0.25
Victorian and Albert Museum, London 3 42 1983
Tate Gallery, London < 4 1980 83
Sainsbury Center, Norwich, U.K. 40 (max) 1981
National Archives and RecordsAdministration, Fort Worth, Texas
2 25 < 42 10 252
National Gallery, Washington, D.C. < 1 Low 7 50
Library of Congress, Washington, D.C. < 0.5 Low 4 145
Baxter Gallery, Pasadena, California 120 1982
Los Angeles County Museum of Art, LosAngeles, California
< 10 1982
Huntington Gallery, San Marino, Calif. < 10 1982
Scott Gallery, San Marino, California 31 92 32 1964
Huntington Library, San Marino, Calif. 75 37
Rijksmuseum, Amsterdam 1 5 1974
Concentration of air pollutants in museums and libraries
Image courtesy of Brimblecombe 1990 and David A. Scott.
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Building SO2(ppm) O3(ppm) NOX(ppb)
NO(ppm)
Dates
Rijksarchief, The Hague < 1 < 1 30 1986
Rijksarchief, Arnhem 1 2 16 1986Rijksarchief, Leewwarden < 1 < 1 ~ 7 1986
Concentration of air pollutants in museums and libraries
Summer measurements
Building SO2(ppm) O3(ppm) NOX(ppb)
NO(ppm)
Dates
Rijksarchief, The Hague 1.5 49 1986
Rijksarchief, Arnhem 4.5 39 1986
Rijksarchief, Leewwarden < 1 ~ 46 1986
Winter measurements
Image courtesy of Brimblecombe 1990 and David A. Scott.
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Marine zone Environment Characteristic behavior of copper
Atmospheric Small sea-salt particles carried by wind.Corrosivity varies with height abovewater, dew cycle, bird droppings, wind,etc.
Partially sheltered surfaces maydeteriorate more rapidly than thoseexposed; top surfaces may be washed freeof salt by rain.
Splash Wet, well-aerated surface, no fouling. Most aggressive zone for may metals andfor protective coatings.
Tidal Marine fouling present to high water. Copper may act cathodically at tidal zone.
Shallow water Seawater saturated with oxygen;pollution, sediment, and fouling may all
be present.
Corrosion may be more rapid than inexposed marine zone areas; a layer of hardshell and biofouling may restrict corrosion.
Continental shelf No plant fouling; some decrease inoxygen, especially in the Pacific, and atlower temperatures.
Copper alloys may be well preserved.
Deep ocean Oxygen varies, lower here than atsurface; temperature near 0C; velocityand pH both lower than at surface.
Data for copper alloys sparse, butcorrosion is limited.
Mud Sulfate-reducing bacteria present;bottom sediments vary in origin,characteristics, and corrosion behavior.
Partially buried bronzes corroded most;submerged copper alloys may be severelyattacked.
Typical marine environments
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Mineralname
Formula Crystal system Color Mohshardness
Cuprite Cu2O Cubic Submetallic red 3.5 4
Tenorite CuO Monoclinic Metallic gray black 3.5
Spertiniite Cu(OH)2 Often amorphous Blue green 1 2 ?
Characteristics of some copper oxide and copperhydroxide minerals
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Pourbaix diagrams for the system Cu-CO3-H2O at various
carbon dioxide concentrations
44 ppm 440
ppm
4400 ppm 44000 ppm
Images courtesy of Pourbaix and David A. Scott.
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Illustration of natural
azurite and malachite
crystal forms
Image courtesy of Palache, Berman, and Frondel 1951 and David A. Scott.
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Mineral name Formula Crystalsystem
Color Mohshardness
Malachite CuCO3 . Cu(OH)2 Monoclinic Pale green 3.5 4
Azurite 2CuCO3 . Cu(OH)2 Monoclinic Vitreous blue 3.5 4
Georgeite CuCO3 . Cu(OH)2 Monoclinic Pale blue ?
Chalconatronite Na2Cu (CO3)2 . 3 H20 Monoclinic Greenish blue 3 -4
Rosasite (Cu, Zn)2CO3(OH)2 Monoclinic Bluish green 4.5
Aurichalcite (Cu, Zn)5(CO3)2(OH)6 Orthorhombic Pearly pale green 1 2
Claraite (Cu, Zn)3(CO3)(OH)4 .4H2O
Hexagonal Translucent blue 2
Characteristics of some basic carbonate minerals
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Shang Dynasty ding,
bronze, shown after
electrolytic stripping.
Image courtesy of Honolulu Academy of the Arts.
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Shang Dynasty ding,
bronze, middle Anyang
period.
Detail, Shang Dynasty
ding. Note black inlay.
Image courtesy of Honolulu Academy of the Arts.
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Shang Dynasty xian
steamer vessel, bronze.
Note black soot on
bottom.
Image courtesy of Honolulu Academy of the Arts.
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Western Zhou Fugeng Li
ding, bronze. 1100-1000
B.C.E.
Image courtesy of Arthur M. Sackler Gallery, Washington D.C.
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Early Western Zhou
Dynasty hu, bronze, 11th
to early 10th century
B.C.E. Photographed
before acquisition by the
Freer Gallery of Art.
Image courtesy of Freer Gallery of Art, Washington, D.C.
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Same Western Zhou
Dynasty hu, photographed
after acquisition by the
Freer Gallery of Art. Note
darker area of corrosion
products where lid joins
vessel.
Image courtesy of Freer Gallery of Art, Washington, D.C.
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Zhou Dynasty gui, bronze, shown during treatment with
cleaned section on the right.
Image courtesy of Freer Gallery of Art, Washington, D.C.
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A. Milne Calder, bronze
statue of William Penn,
cast 1889-91, City Hall
Tower, Philadelphia.
Image courtesy of Andrew Lins and Tracy Power
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BF x96 from the William Penn figure: a complex, multilayer
corrosion crust can develop on bronzes after long exposure to
urban-industrial atmospheres in this case 97-98 years. The
corrosion is approximately 200 microns thick and partly
follows
microstructuralfeatures, especially
casting pores
located near
the surface.
Image courtesy of Andrew Lins and Tracy Power
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BF x240 also from the William Penn figure, illustrates that
the delta phase is not as rapidly attacked as the alpha phase
at this particular site.
Image courtesy of Andrew Lins and Tracy Power
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BF x310 shows the irregular, porous nature of the mineral
formations within the crust.
Image courtesy of Andrew Lins and Tracy Power
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This three-dimensional plot shows the stability of different
copper minerals in water at 25C. Below are oxidized copper
species found in rain or natural waters. The x axis shows pH,
the y axis shows
sulfate ion activity,
and the z axisshows total CO2
activity (including
CO2(g), H2CO3,
HCO3-
, and CO3=
).Zone of conditions
favoring antlerite
formation is
shaded.
Image courtesy of Andrew Lins and Tracy Power
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Plot emphasizing the calculated lower limit of cupric ion
activities (aant v broch) which would allow antlerite rather than
brochantite to form,
based on the work
of Silman.
Image courtesy of Andrew Lins and Tracy Power
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Plot showing the solubility of different copper sulphate and
oxide species in dilute sulphuric acid solutions. Data basedon thermodynamic and
other calculations at 25C,
after Mattson and Graedel.
Zones for acid rain and fog
are displayed, overlaps
indicating which minerals
are likely at particular pH
levels and sulphate
concentrations. The leftside shows no stable
mineral forms, only
Cu++ in solution.
Image courtesy of Andrew Lins and Tracy Power
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The site of Francavilla, Southern Italy, 5th-6th C BC.
Bronze tripod legs of anthropomorphic form.Image courtesy of Bolletino dArte.
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The site of Francavilla
Image courtesy of Bolletino dArte.
From left to right,
top to bottom:
Extensive working and
annealing to shape,
followed by cold-working of
the surface.
Very small crystallized
grains. Copper sulfideinclusions are visible.
Variable grain size with
intergranular corrosion.
Typical corrosive
penetration along slip
planes in the bronze
crystals infilled with cuprite.Corrosion crust principally
of malachite.
Uneven intergranular
attack.
Overall view.
Recrystallized small grain
structure.
Sulphide and leadinclusions and very large
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Pourbaix diagrams for the system Cu-Cl-H2O at various
carbon dioxide concentrations
35 ppm 350
ppm
3550 ppm 35500 ppm
Images courtesy of Pourbaix and David A. Scott.
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Pourbaix diagram for
the system Cu-SO4-H2O.
Images courtesy of Pourbaix and David A. Scott.
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Pourbaix diagram for
the system Cu-S-H2O.
Image courtesy of Schweizer.
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Images courtesy of David A. Scott.
Surface corrosion
containing pustules of
copper and lead salts.
Surface of the Roman
bronze statue of Romaor Virtus showing
fibrous malachite
occurring as curled
crystals.
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Image courtesy of the Getty Museum.
Miniature Portrait Bust
of a Woman, Roman,25 BC - 25 AD. Bronzewith glass-paste inlays.
The bust is shown
before conservation,
illustrating pustularcorrosion with pitting
created by bronze
disease.
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Images courtesy of David A. Scott.
Two small penannular bronze nose ornaments from the site of La
Compania, Ecuador, dated to about the tenth century CE, showing the light
green, powdery eruptions typical of bronze disease.
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Measures for wet metallic objects: bronze, brass, lead and
silver can generally be allowed to dry out. Iron may be
better stored in oxygen-free environment, can use oxygen
scavengers in sealed jar or box, silica gel, or store in water
with sulphite added to mop up oxygen. Silica gel may not
be enough for heavily corroded iron.
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The monument of MarcusAurelius after restoration
Image courtesy of The Mr. and Mrs. Lawrence Fleischman.
Before
After
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Elemental distribution
maps for sulfur, lead, tin
and carbon, together with
secondary-electron and
backscattered electron
images (top).
Magnesium, copper,
chlorine and oxygen with
secondary-electron andbackscattered electron
images (bottom) for a de
Vries bronze statue.
Images courtesy of David A. Scott.
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Elemental distribution
maps for a bronze
statue of Alexander
Hamilton, New York,
erected 1890:
Copper(top left)
Tin (top center)
Chlorine (top right)
Oxygen (bottom left)
Zinc (bottom center)Images courtesy of David A. Scott.
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Image courtesy of David A. Scott.
Togati pustule
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Image courtesy of David A. Scott.
Togati pustule
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Votive bronze leaf
Narrow leaf formed of thin sheet
bronze, with a prominent central rib.
Bottom: view of a section of leaf
showing voids that suggest selective
corrosion of the alloy due to
differential composition.
Image courtesy of David A. Scott.
Magnificationx100, crossed
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Bronze flower rosette.
Six joining frr preserving much
of rosette. Rosette with at
least eight petals, and
perhaps originally as many as
eleven. Hole in center; nopreserved rivet
Image courtesy of Bolletino DArte: the Archaic Votive Metal Objects.
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Right: Overall view of rosette, unetched,
showing cracking and inter-granularcorrosion.
Bottom right: View of etched section
showing small twinned grains and inter-
crystalline corrosion.
Bottom: etched in ammonia peroxide
showing strain lines in the surface areas.
Magnification x50
Image courtesy of Bolletino DArte: the Archaic Votive Metal Objects.
Magnification
x250
Magnification
x100
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Bronze votive floral sprays.
Two joining flowers, plus
miniscule flower, preserving
complete rod, with portions of
terminals at both ends. Bent,
as shown. Somewhatcorroded.
Image courtesy of Bolletino DArte: the Archaic Votive Metal Objects.
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Right: View of votive floral spray
showing the corrosion crust tat
displays extensive Liesegang-type
phenomena in a cuprite and
malachite crust.
Bottom right: Etched view
showing twinned grains with
corrosion through strain lines.
Magnification
x12.5
Image courtesy of Bolletino DArte: the Archaic Votive Metal Objects.
Magnification
x100
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Preserve unique version of
Greek language.
Made in pure copper
Corrosion considered odd
Thought to be a forgery by
some German scientists
Need to confirm their
authenticity as very important
for the history of language.
One plaque in Johan von
Wagner Museum: Stuttgart,
another two in Norway, one
lost in a private collection.
Image courtesy of West Semitic Research.
Copper plaque.
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Greek Copper Plaques
Image courtesy of West Semitic Research.
Copper plaque.
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Radiographic examination used
to read inscribed text on backand front without further
cleaning.
Chemical analysis
X-ray fluorescence studies X-ray diffraction studies
Metallographic studies
Here the hammering marks in
the x-ray image are importantas same on all three plaques.
Text is from 8th-9th century BC
Greek evolving from Phoenician
at this time. Get digamma and
qoppa used.Image courtesy of West Semitic Research. Copper plaque, X-radiograph.
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Corrosion on one very
heavily chloride-
containing.
This was atacamite and
paratacamite, two of the
copper trihydroxychlorides
Cu2(OH)3Cl.
German argument was
that this is not acceptable.
Argument based on usual
predominance of
malachite and carbonates
in soil burial corrosion.
Image courtesy of West Semitic Research.
Copper plaque.
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Detailed surface examination showed inscribed letters
preserved within corrosion, not metallic substrate.
Image courtesy of West Semitic Research.
Copper
plaque,
detail of
inscription
s.
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ESEM studies showed pseudomorphic preservation of wood
cellular structure within copper corrosion products of malachite.
Note spiral thickening of cell wall and some pits.
Image courtesy of West Semitic Research.Copper plaque. Copper corrosion has replaced the wood
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Minute wood and some charcoal fragments preserved within
corrosion crust.
Image courtesy of West Semitic Research.Copper plaque with attached
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More examples of pseudomorphic preservation of cellular
wood structure.
Images courtesy of David A. Scott.
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Metallographic examination reveals coherent cuprite layer
beneath thick green corrosion crust contiguous with metal
Image courtesy of West Semitic Research.Copper plaque microstructure.
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Mineralogical complexity to this corrosion crust
Image courtesy of West Semitic Research.Copper plaque microstructure.
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Argument for authenticity too
strong: Surface preserved within corrosion.
Coherent cuprite layer
Pseudomorphic replacement of
wood
Hammering marks of the plaques
Knowledge that pure copper was
used for other artefacts
Corrosion acceptable
Conclusion: previous view thatplaques are fake is totally incorrect.
Based on a superficial view that
patinas primarily of copper
chlorides do not exist, which is
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