Modified after the talk presented at AITA2013 - http://ronchi.isti.cnr.it/AITA2013 The talk was mentioned for the "Ermanno Grinzato" Under 35 Best Paper Award (http://ronchi.isti.cnr.it/AITA2013/award.html) The talk was based on the paper Conservation of historical frescoes by timed infrared imaging analysis by G. Cadelano, P. Bison, A. Bortolin, G. Ferrarini, , M.Girotto, F. Peron, M. Volinia, AITA2013 Abstract Book, p 61-64, 2013

1. G. Cadelano, P. Bison, A. Bortolin, G. Ferrarini, M.Girotto, F. Peron, M. Volinia
Conservation of historical frescoes by timed
infrared imaging analysis
Istituto Tecnologie della Costruzione
Consiglio Nazionale delle Ricerche
Università IUAV
di Venezia
AITA 201312th International Workshop on
Advanced Infrared Technology and
Applications
Politecnico
di Torino

2. Introduction | Case study | Experimental procedure| Data collection | Conclusions
Water presence is considered the primary
threat to the cultural heritage
conservation.
The salt efflorescence/subflorescence is the
effect of the crystallization of solvated salt
occourring after the evaporation of the
solvent (water).
This phenomenon is associated with the
presence of recurrent cycles of wet and dry
inside the walls.(=solvatation and
crystallization)
water damage to mural paintings

3. Introduction | Case study | Experimental procedure| Data collection | Conclusions
The conservation of cultural heritage requires the monitoring of the
phenomena involved in the process of decay of artworks.
In most circumstances quantitative local methods are not appropriate, and
often are prohibited, to be applied to cultural heritages due to their invasive or
destructive characteristics.
Literature shows that quantitative thermography is an outstanding instrument
for accurate thermal analyses of buildings, also in historical architectures, in
order to monitor indoor and outdoor surfaces and to evaluate the distribution
of moisture.
This work represents an attempt to combine some data acquisition and signal
processing methods typical of the NDE applications with an advanced infrared
acquisition system.
IR thermography and wall moisture

4. Introduction | Case study | Experimental procedure| Data collection | Conclusions
St. Eldrad’s chapel is an isolated structure of the Abbey of Novalesa complex, located
about 60 Km west of Turin, Italy.
The building measures 8 x 5.8 meters inside and dates back to the 11th century and is
preceded by an atrium built in the second half of the 17th century.
St. Eldrad’s chapel
The internal walls and ceiling are completely decorated with fresco paintings that date
back to the second half of the 11th century, depict the iconographic cycles of St.
Nicholas and St. Eldrad.

5. Introduction | Case study | Experimental procedure| Data collection | Conclusions
No conservation problems for
many centuries, until recent
times.
Serious damages started to
be evident soon after
restoration works, which
included:
• the removal of the outer
plaster layer;
• the closure of a window in
the South side;
• a trench was escavated
along the northern
external wall.
degraded wall paintings
NORTH
SOUTH

6. Introduction | Case study | Experimental procedure| Data collection | Conclusions
The stimulus in this active thermography application is the solar radiation that
can be considered as a periodic stimulus with period equal to one day. The
corresponding physical phenomenon is a thermal wave that propagates from
the outer surface of the building toward the inside of the chapel.
Observing the temperature of the wall from inside, assuming evenly space
distributed solar radiation, and wall thickness and stratigraphy as
homogeneous, the water content of the wall is expected to have a main role
in eventual thermal anomalies.
active thermography technique
day 11
day 10
day 9
day 8
day 7
day 6
day 5
day 4
day 3day 2
day 1
North
South
East
West
T [ C]
t
Indoor air temperature

7. Introduction | Case study | Experimental procedure| Data collection | Conclusions
The inner surface temperature oscillates with the same period of the heat flux.
The amplitude of the oscillation depends on the thermophysical properties of
the wall; its phase is delayed by wall thickness and characteristics.
T [ C]
tday 10 day 11
detrend(Tblue,Tgreen)
active thermography technique

8. 0 24 48
Introduction | Case study | Experimental procedure| Data collection | Conclusions
dry vs wet
material λ [W m-1 K-1] ρ [Kg m-3] Cp [J Kg-1 K-1]
Clay bricks 0.5 1800 840
Marble 2.8 2600 800
Pietra Serena 2.45 2540 811
Concrete 1.0 2100 880
Water 0.6 1000 4182
m =
1
k
wet
wet
wet
C )(

 
total
void
V
V
f  T(x,t)µ A( f )e-kx
cos(wt -kx)
0 24 48
0 24 48
24 hrs period
t
t
t
Wet wall
Heat flux
IR camera
)cos( t
OHdrywet
f 2
 
OHdrywet
CfCC 2
)()()(  
drydrydry
C,, 
Dry wall
Dk = kdry -kwet
T
T
kdry =
w
2adry
kwet =
w
2awet
adry =
ldry
(rC)dry
Thermal diffusivity
Penetration depth
Phase shift
OUTSIDE INSIDE

9. Introduction | Case study | Experimental procedure| Data collection | Conclusions
aIRview is a robotic monitoring system that consists of optical sensors for the detection
of heat flows and special sights designed to be used in the infrared range.
aIRview can be used to automatically acquire and process thermal images of wide areas
in short time, with 1 pixel=1 cm resolution.
Geometrically correct reconstruction of surface temperatures is obtained through the
correction of optical distortions and automatic mosaiking process.
robotized thermographic system

10. Introduction | Case study | Experimental procedure| Data collection | Conclusions
aIRview can be remotely programmed and controlled.
The processed data are automatically uploaded in the internet and are downloadable by
the users as ready to use results in real time through the aIRview website.
aIRview has been used to monitor three inside walls of St. Eldrad’s chapel (South, West
and North), every 15 minutes for 11 days.
remote monitoring

11. signal processing
TEMPERATURE[C]
NORTHSOUTH WEST
Introduction | Case study | Experimental procedure| Data collection | Conclusions
The algorithm applied to the sequences of thermal images has been a Fast Fourier Transform.
Analyzing the function from the time domain, shown in red, to the frequency domain, in blue,
the component frequencies, spread across the frequency spectrum, are represented as peaks in the
frequency domain.

12. Introduction | Case study | Experimental procedure| Data collection | Conclusions
image processing results
NORTHWESTSOUTH
PHASEAMPLITUDEVISIBLE

13. Introduction | Case study | Experimental procedure| Data collection | Conclusions
South wall results
VISIBLEPHASE

14. Introduction | Case study | Experimental procedure| Data collection | Conclusions
The chosen case study has been particularly challenging due to its peculiar
context that required special hardware.
Analyzing the damaged South wall with FFT amplitude and phase, has been
possible to attempt to explain the decay mechanism related to moisture
presence, as effect of wet/dry cycles that cause alternate salt solubility and
crystallization.
The particular shape of the boundaries of the deteriorated areas and the strong
presence of salt efflorescence is conducible to wall moisture phenomena, such
as the capillary action from the ground and the rain infiltrations.
goals

15. Introduction | Case study | Experimental procedure| Data collection | Conclusions
Seasonal measurements (changes in the pattern of moist areas, test
repeatability)
Comparison with software modeling (input data)
Microclimate analysis (moisture contribution from tourists and air humidity
variations, air flows)
extras

16. Thank you for your attention
contact: gianluca.cadelano@itc.cnr.it
Novalesa Abbey