This presentation is aimed at providing to high school students, an introduction to green staining of copper on masonry structures observed in copper architecture. This is purely an educational activity, mainly prepared by two AP Chemistry Students (Yang Hui and Ashley Steele) from Luella High School, Locust Grove, Georgia. They intend to share this compilation for other students to benefit from, and explore the wonderful world of copper architecture.

1. Renuka Rajasekaran
Luella High School
Renuka.Rajasekaran@henry.k12.ga.us

2. About this presentation
This presentation is aimed at providing to high school students, an introduction to
copper architecture and its merits. This is purely an educational activity. We intend
to share this compilation for students and teachers of chemistry to benefit from so
that they would explore the wonderful world of copper architecture.
It is truly an excitement for students to see how the simple chemistry principles,
learned in the high school curriculum help understand the real world problems.
Copper architecture is full of very interesting and practical chemistry problems that
connect very aptly to chemistry curricula. Chemistry of copper architecture can
help make outstanding science fair projects. Teachers can design interesting lessons
and labs for chemistry courses. At our end, we took interest in investigating the
problem of green staining by copper on masonry structures. There is absolutely no
limit to how much one can explore in copper architecture.

3. Since 5,000 BC, copper has been an indispensable companion of human
civilization and its use has continuously expanded over time (this video
on copper is inspirational). Besides other uses, copper is being
increasingly considered for architectural applications and today, there is
hitherto unforeseen application of copper in building constructions.
There are various merits for copper, which make it an ideal candidate for
construction and architectural applications; for instance: superior
corrosion resistance, high fatigue resistance, very good electrical and
thermal conductivity, and ease of fabrication besides its natural beauty.
(Here is an excellent article on copper’s natural beauty and this video
speaks of the eco friendliness and sustainability of copper in architecture)
Talking of corrosion resistance, we need to understand that corrosion is
the process of the interaction of a metal or an alloy with its environment.
Corrosion deals with time-related changes to metal or alloy in its
environment. Such changes may be reductive (resulting in loss of mass),
additive (resulting in addition of mass, e.g. patina) or transformational
(resulting in chemical or physical changes of the surface after the additive
process).
Copper beautifully takes corrosion to its advantage: in the presence of
moisture, salt and high sulfur pollution, copper quickly begins to oxidize
and progresses through the weathering process. The natural green patina
we see on historical buildings is due to this weathering process of copper.
Watch this video on the Statue of Liberty. A few examples for outstanding
coper architecture are shown on the right.
Chateau hotel in Canada built in 1890; Picture
Courtesy: Google Free Images.
https://landlopers.com/2013/01/17/chateau-
frontenac
Copper Architecture has a Long and Rich History
Alexander Nevsky Cathedral, Sofia, 1904;
Picture Courtesy:
https://en.wikipedia.org/wiki/Alexander_N
evsky_Cathedral,_Sofia
Sun Tower (aka World Building in British
Columbia, 1912; Picture Courtesy:
https://en.wikipedia.org/wiki/Sun_Tower

4. It is quite interesting to observe the morphology of aged pennies
with naked eye, with magnifying glass, and with microscope. As the
resolution is increased more details are revealed.
The weathering of copper is an equilibrium process, and there are
several stages of maturation in this equilibrium. Evidently, there is a
range of chemical conversion processes accompanying the weathering
/aging od copper. Here is the copper weather chart published by the
Copper Development Association Inc.
https://www.copper.org/applications/architecture/arch_dhb/technical-
discussion/fundamentals/arch_considerations.html#weathering_chart (Picture Courtesy: Google
Free Images)
Although these colors represent a typical sequence, the course of weathering of any copper
structure exposed to atmosphere will depend on various environmental factors, including,
orientation, sophistication of the structure, and the dimensions.
Slow, Slower, Slowest: Color Progresses Steadily;
It is Meticulously Time Framed
Unexposed 4 Months 8 Months 1 Year
2 Years 3 Years 4 Years 5 Years
7 Years 10 Years 15 Years 25 – 30 Years
Students at Luella High School are examining the morphology of pennies

5. The initially formed copper oxide (cuprite [1]) is responsible for a gradually
progressively more brown-black surface appearance. Then on, the surface
green color undergoes several chemical reorganizations in composition to
get more coherent and integrated coating, with the underneath cuprous
oxide layer still remining intact.
The top layer is usually basic copper sulfates and or chlorides, which make
the surface greenish.
Basic copper(II) chlorides atacamite, paratacamite and
botallackite are more greenish than the basic sulfate. Copper
near coastal environments get greener quickly than those
inland.
The First Chemical Transformation is
Understood as the Formation of Cuprous Oxide
References:
1. Yolanda Hedberg and Inger Odnevall Wallinder
Journal of Environmental Protection, 2011, 2, 956-
959.
2. Geological Survey Professional Paper, Volumes 275-279;
https://books.google.com/books?id=hkJSAQAAMAAJ&dq=c
uprite+turns+into+chalcocite&source=gbs_navlinks_s
3. Allen Garrison, J. Phys. Chem., 1924, 28 (3), pp 279–284.
3. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of
the Elements (2nd ed.). Butterworth-Heinemann.
p. 1185. ISBN 0-08-037941-9.
4Cu + O2 → 2Cu2O
2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2
Cu2S + 2 Cu2O → 6 Cu + SO2
2Cu2O + O2 → 4CuO
2 Cu + S → 4CuS
2CuO + CO2 + H2O → Cu2CO3(OH)2
3CuO + 2CO2 + H2O → Cu3(CO3)2(OH)2
4CuO + SO3 +3H2O → Cu4SO4(OH)6
6 CuCl + 3/2 O2 + 3 H2O → 2 Cu3Cl2(OH)4 + CuCl2
Ageing of copper in nothing but minerology in action; several chemical reactions take place
during the ageing process. A sample of such reactions [2] are listed in the box below. This is
not an exhaustive listing. Which reactions dominate at a given time, depends on so many
environmental conditions and purity of the metal. Because of the unique combination of
facts and factors, chemical reactions not normally possible do conveniently take place on
the top of copper exposed to the natural atmospheres over a long period of time. Several
of these reactions are accelerated by the photosensitivity of cuprous oxide [3] and cuprous
chloride [4] as well as the dehydration, deliquescence, and efflorescence of several
compounds involved.
Whether or not water is directly involved in the reaction, presence of
water is an indispensable requisite as it aids several phase transfers
plus hydrate transformations; this will explain the influence of
humidity on patina formation on copper. Like water, the presence and
pressure of carbon dioxide in the environment influences the patina
formation.

6. COLORS OF AGEING – RESONATING WITH NATURAL RHYTHM
Red-Green Synchronization: Colorado River: Picture Courtesy:
Free Images from: ttps://pixabay.com/en/usa-colorado-river-
horseshoe-bend-2075213/
From left to right, pure water, solutions
of copper chloride 0.5 M, 0.75 M, 1 M,
2.5 M, 5 M, 7.5 M, 10 M, 12.5 M, 15 M,
and copper chloride dihydrate
Colors of Copper Oxide films in Gold-brown,
Violet-blue, Blue, Gold-green, Pink, and Pearl
have also been developed.
(Source:
https://www.researchgate.net/publication/234863
665_Transpassive_Dissolution_of_Copper_and_R
apid_Formation_of_Brilliant_Colored_Copper_Ox
ide_Films); Reproduced with permission from the
Journal of the Electrochemical Society
Red and Green Colors of Foliage: Picture Courtesy: Google Free
Images
Colors of Thin Films of Copper Sulfide on
Copper; Picture Courtesy:
http://www.microlabgallery.com/gallery/1%2
0thru%204%20orders%202.aspx
Reproduced with permission
Copper takes all the beautiful colors of
natural chemistry
In solution and solid state, we see all
colors in copper from red-orange to
Green with yellow missing. Copper
sulfide says, “Copper is also gold and
yellow.” Several copper alloys used in
construction
Colors of copper and various copper alloys used in
building structures.; Picture Courtesy:
https://en.wikipedia.org/wiki/Copper_in_architecture
CopperColorsblendwithcolorsof nature

7. In copper architecture, patina deserves a special significance, as it is being increasingly
used in buildings both for aesthetics and sustainability.
Copper patinas are used in all the three components of a building:
Roofs
Walls
Floors
In general, copper patinas are classified into three types:
(1) Acquired patinas
(2) Applied patinas
(3) In situ generated patinas
Acquired patinas are the surface color modifications due to natural weathering process.
Applied patinas are chemically induced on the metal; it is an accelerated patina. Many
modern copper buildings have applied patinas on metal/alloys cladded on them.
Using alloys of copper, patina colors normally not possible with copper alone can be
developed. On the right, some famous copper architectural pieces are provided. The Burt
Church is an acquired patina, naturally developed on the copper roofing. It has been partly
repatinated.
Picture Courtesy: http://www.edgeformmetals.ie/metals-page12767.html
Bon Secours Hospital at Galaway, Ireland won the RIAI
award for Best Health Building, 2007. The cladding on
this hospital is made from CuAl5-grade copper and
aluminum alloy . The original golden green color of the
surface goes through characteristic changes when
exposed to normal weathering. Picture Courtesy: Google
Free Images
Whites Hotel at Wexford in Ireland is an example
for applied copper patina architecture.
Picture Courtesy: Google Free Images
Burt Church, Donegal, called the ‘Building of
the Century’ has a recently applied bright
copper alongside the original naturally
patinated copper.
Picture Courtesy; Google Free Images.
ACQUIRED, APPLIED, AND IN-SITU PATINAS ON COPPER
There are simple chemical techniques to
create patinas on copper; here is one
demonstration

8. Copper Architecture Awards
• Around the world, several organizations exist to
promote copper in architecture. We are witnessing an
unprecedented growth in copper architecture.
Aesthetics, durability, ease of maintenance, etc. make
copper architecture a much sought after style.
• Copper Architecture awards are given to outstanding
buildings
• Tough competitions exist to win these awards.
• Some outstanding buildings with copper architecture are
shown here; Source for Pictures:
http://www.architecturaldigest.com/gallery/worlds-best-
copper-buildings-slideshow/all ; Picture Courtesy: Google
Free images

9. However, there is one problem
with copper architecture

10. Some Reports show Green Staining on Masonry in Some Structures: This
Problem Needs to be Addressed
https://www.youtube.com/watch?v=TzYNiZapcM4
Reproduced with permission
http://file.scirp.org/pdf/JEP20110700012_37240764.pdf
Reproduced with permission
Copper Staining on Masonry Structures:
(Top Left) A section of student audience at a presentation
on copper architecture at Luella High School, Georgia;
(Top Middle) A new Building with copper staining on
stucco during the first bloom; (Top Right) a 800-year old
building in Stockholm, with copper staining on bricks
(reported in 2011); (Bottom Left) Copper staining on a
historic building at Wacker Drive in Chicago found during
a restoration project (reported in 2005); (Bottom Right)
Copper stains on the floor from the copper run off from
copper roofing (reported in Washington Post in 2016).
http://www.masonrymagazine.com/9-05/cleaning.html
Picture Courtesy: Google Free Images
https://www.washingtonpost.com/lifestyle/home/
how-to-remove-copper-stains-from-
concrete/2016/01/29/70185a14-c070-11e5-83d4-
42e3bceea902_story.html
Picture Courtesy: Google Free Images