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POLLUTED RAIN AND MONUMENTS
The pH of rainwater usually has a value of 5.5,
allowing the life of flora and fauna without damaging
resistant rocks like marble.
MARBLE
Thanks to the chemical and
mechanical resistance to
weathering, since ancient times
marble was used to decorate
prestigious buildings with
capitels, columns or even
statues and monuments.
However, the industrialization of the nineteenth
century led to the increase of gas in the atmosphere,
above all components as:
1. Dioxide and sulfur trioxide (SO2 and SO3)
2. Nitrogen dioxide (NO2)
3. Carbon dioxide (CO2)
T H E S E G A S E S R E A C T W I T H T H E H 2 O, G I V I N G T H E F O L L O W I N G A C I D S
1.SO2 + H2O ---> H2SO3 (sulphorous acid)
2.SO3 + H2O ---> H2SO4 (sulfuric acid)
3.2NO2 + H2O ---> HNO2 + HNO3 (Nitrous Acid and Nitric
Acid)
4.CO2 + H2O ---> H2CO3 (carbonic acid)
These reactions can lower the pH value up to 2,
resulting in a serious damage especially to the
marble changing it from calcium carbonate (CaCO3)
in gypsum (Calcium sulfate: CaSO4), more easily
damaged by atmosphere agent.
Rainwater removes the gypsum that has been
formed and so a new portion of the marble is
exposed to the action of acid rain with a consequent
progressive and continuous erosion of the building
or of the artifact artistic.
The blackening
and air pollution
I TA LY H A S T H E G R E AT E S T C O N C E N T R AT I O N O F H I S T O R I C A L A N D A R T I S T I C H E R I TA G E O F T H E W H O L E W O R L D
In the national territory, over 60,000 areas of
cultural interest have been registered in the risk
map (icr 1996).
In recent decades there has been a rapid
degradation due to pollution as the major cause.
The decay of a work of art begins immediately
after its completion and the speed depends on the
materials and external agents.
The speed of action is increased by the presence of
carbonaceous particles to which are attributed also
the blackening on stone surfaces of monument or
historic building.
Air pollution affects especially the degradation of
the artistic heritage as determines the change of the
gases and causes harmful chemical reactions.
Limiting greenhouse effects meets the protection of
art.
The index of biological contamination takes into
account the level of biological events on monuments.
THE ORGANISMS PRESENT ON THE WORKS OF ART CAN BE:
• Natural , i.e. lichens, mosses
1. These are deposited on the surface of monuments
2. Frost3. Salt Crystallisation4. Microclimate5. Thermal shock6. Chemical
• Anthropic ( caused by humans activities )
1. Pollution 2. Acid rains
We can infer the degree of microorganism
colonization by sampling the sediments and
calculating the amount of ATP (adenine-tri-
phosphate).
In 1995 the Ministry for Cultural and Environmental
Heritage promoted the Risk Map of Italian Cultural
Heritage.
It still protects our territory and provides its
members instruments for scientific and
administrative support.
The risk map also allows us to calculate the risk of
loss of all cultural heritage and to know their
distribution on the Italian territory
The first ever comprehensive evaluation of the
factors of degradation was made in Umbria which
proved to be effective in the dramatic occasion of the
earthquakes in Friuli.
THE MOST AGGRESSIVE SUBSTANCES FOR
MONUMENTS
CARBON DIOXIDE : it’s a natural component of the atmosphere.
In these years the concentration of CO2 has increased because of the fossil fuels adopted in
the domestic heating and in industrial processes.
Calcareous stone artefacts and calcareous
Sandstones are dissolved by slightly
acidulate water.
SULPHURE COMPOUNDS (SO X )
It’s principally present in the atmosphere as
sulphur dioxide (SO2), hydrogen sulphide (H2S)
and sulphates (SO4).
In combustion processes sulphure is oxidized
into sulphur dioxide(SO2).
The presence of sulphure oxides in the
atmosphere is the reason for the formation of
gypsum.
The latter concerns stone material and bronze.
This process causes the loss of the superficial
layer of the material.
OXIDES OF NITROGEN(NO X ) :
They are all the compounds between nitrogen and
oxygen in the different oxidation states.
Generally nitrogen oxides are oxidized in the atmosphere
by nitronic acid that corrodes the material surface.
ATMOSPHERIC PARTICULATE
They are carbon particles produced by the
combustion of fossil fuels wich settle on stone
artefacts, bronzes, paintings and frescoes damaging
them.
ATMOSPHERIC PARTICULATE
All the kinds of particles can be found in the black
crusts that cover monuments.
T H E PA RT I C U L AT E B E C O M E S A N I N T E G R A L PA RT O F T H E M AT E R I A L
T H AT F O R M S T H E M
The substances that can deteriorate a work of art may
be released from different sources like:
-COMBUSTION PROCESSES: like carbon dioxide,
sulphur dioxide and carbon particles;
-MEANS OF TRANSPORT: that produces carbon
nitrogen and sulphur oxides and particulate;
-PROCESSING ARTEFACTS: that introduce in the
atmosphere sulphuric anhydride , hydrochloric acid ,
nitrogen oxides and particulate
GOOD CONSERVTATION PRACTICES
The synergy of both physical and chemical factors determines the degradation of a work of art, which causes subsequent restoration and cleaning. The resulting cultural loss is difficult to estimate in monetary terms, because of the intrinsic value of many artistic artefacts. Restoration and consolidation practices are often neither decisive nor definitive and must be repeated at regular intervals.
GOOD CONSERVTATION PRACTICES
The key objectives to be achieved in the protection and
conservation of works of art can be listed as follows:
Slowing down of the
degradation and
consequent reduction in the
loss of the original material
Restitution and preservation of the aesthetic contents of the monument
I T I S E S T I M A T E D T H A T, O N A V E R A G E , T H E R E S T O R A T I O N O F A R C H I T E C T U R A L S U R F A C E S C O S T S F R O M 5 0 0 T O 7 5 0 €
P E R S Q U A R E M E T R E .
This cost must be added with
Security charges Design charges Charges for provisional
deeds
Therefore, we can consider that the cost of the
restoration reaches 1,000 - 1,500 € per square metre
of surface. For example in Rome, as a rule, the
restoration of surfaces, is performed at regular
intervals of 25-30 years, corresponding to the
Jubilees
The management system of geographic information
allows us to represent on the risk map the
relationship between territorial municipalities and
distribution of cultural heritage.
M I N I N G T O W N O F T U R I N A N D S U P E R I M P O S I T I O N O F C U L T U R A L B E L O N G I N G
M I N I N G T O W N O F N A P L E S A N D S U P E R I M P O S I T I O N O F C U LT U R A L
B E L O N G I N G
Scientific Experiment
To prove the truth of transformation of marble to gypsum, we
conducted an experiment in the school laboratory, by the reaction of hydrochloric acid and sulfuric acid on stones such as marble and travertine.
Scientific Experiment
Usually the sulfuric acids make these stones easy to damage but we did this experiment also with hydrochloric acid to accelerate this process.
To realize the experiment, we needed the following materials:
- A piece of marble; - A piece of travertine; - Hydrochloric acid; - Dropper; - Sulfuric acid.
Materials
Once positioned the piece of marble and travertine for the
experiment, we dropped some sulfuric acid on marble and travertine.
Step One
Marble Travertine
As soon as let the acid, it reacted making
bubbles.
Step One
Marble Travertine
We repeated the experiment substituting sulfuric acid with
hydrochloric acid to have a faster reaction although usually the surfaces are transformed by sulfuric acid.
Step Two
Marble Travertine
In fact, the reaction we obteined with the
hydrocloric acid, was more visible and immediate then the other.
Step Two
Marble Travertine
However, although hydrochloric acid had accelerating the
process, before the final result we had to wait a day to see that the surface on which the solution had been applied, had become gypsum.
Step Three
Thanks to this experiment we have seen how due to acid rain,
in the long run (because of the low concentration of sulfuric acid) the marble becomes gypsum and then more subject to degradation.
Conclusion