1 Chemistry Central Journal 2012 Vol: 6(1):145. DOI: 10.1186/1752-153X-6-145

Microclimate monitoring of Ariadne’s house (Pompeii, Italy) for preventive conservation of fresco paintings

Ariadne’s house, located at the city center of ancient Pompeii, is of great archaeological value due to the fresco paintings decorating several rooms. In order to assess the risks for long-term conservation affecting the valuable mural paintings, 26 temperature data-loggers and 26 relative humidity data-loggers were located in four rooms of the house for the monitoring of ambient conditions. Data recorded during 372 days were analyzed by means of graphical descriptive methods and analysis of variance (ANOVA). Results revealed an effect of the roof type and number of walls of the room. Excessive temperatures were observed during the summer in rooms covered with transparent roofs, and corrective actions were taken. Moreover, higher humidity values were recorded by sensors on the floor level. The present work provides guidelines about the type, number, calibration and position of thermohygrometric sensors recommended for the microclimate monitoring of mural paintings in outdoor or semi-confined environments.

Mentions
Figures
Figure 1: Plan of Ariadne’s house. Lodgings marked as 1 to 4 are the only roofed ones (parallel tilted lines delimit the covered area). Data-logger #1 was located on the top of an outside wall next to room 3 at 3 m from the ground level and it was covered with a ceramic tile. Figure 2: Calibration of RH and temperature sensors. Difference between RH and temperature recorded by each probe with respect to the average from all probes in two different calibration periods: first, from 18th to 21st July 2008 (a: RH; b: temperature) or second, from July 31st to August 28th 2009 (c: RH, d: temperature). Trajectories were smoothed using a moving average with a window size of one day. Figure 3: Smoothed time series of RH and temperature. Average RH (a) and temperature (b) recorded by all probes (except #1) during one year (day 0 corresponds to July 23rd 2008). The time series was smoothed using a moving average with a window size of one day. Horizontal lines in red correspond to the ranges recommended by the standard DM 10/2001 for the conservation of mural paintings. Figure 4: Trajectories of RH (a) and temperature (b) recorded by all probes during three summer days (23rdto 25thJuly 2008). Vertical lines correspond to midnight (0:00 hr). Figure 5: Temperatures in room 4. Temperatures recorded by data-loggers in room 4 (#2, #3 and #4) during four summer days (4th to 8th August 2008). Values of #1 are also shown for comparison. Figure 6: Location of probes #2, #3 and #4 in room 4. The picture was taken at 1:05 PM. The brighter zone at the lower right corner corresponds to sunlight incident on the frescoes that affects #3 from 2:00 PM to 8:00 PM. Figure 7: Maximum daily differences of temperature between data-loggers #3 and #4. Calculated for the 372 days of the period under study (day 0 corresponds to July 23rd 2008). Figure 8: Abnormal peaks of temperature recorded in room 4 and 3. Temperatures recorded by probes in room 4 (a) and five probes in room 3 (b) during four winter days (19th to 23rd February 2009). Values from #1 are also included for comparison. Figure 9: Mean daily trajectories of temperature and RH in summer. a) Temperature at rooms 1 and 3; b) temperature at rooms 2 and 4; c) RH at rooms 1 and 3; d) RH at rooms 2 and 4. Summer period: 7/23/2008 to 9/20/2008. Color codes indicate the location of probes: room 1 (green), room 2 (blue), room 3 (violet), room 4 (red). The thicker black line corresponds to the average time series of all probes. Figure 10: ANOVA results (room 2). ANOVA results showing the differences among probes in room 2 on the daily mean RH recorded in summer 2008. For each data-logger, the average and 95% LSD interval is depicted. Codes indicate the wall orientation where each sensor is facing (N: north; S: south, E: east, W: west) and the height: f (floor level), u (upper) or i (intermediate). Figure 11: ANOVA results (rooms 1 and 3). ANOVA results (average and 95% LSD intervals) showing the differences among probes in room 1 (a) and 3 (b) on the daily minimum RH recorded in summer 2008. The codes indicate the wall orientation (N: north, S: south, E: east, W: west, and M: mosaic) and the height: f (floor level), i (intermediate) or u (upper). Figure 12: Mural frescoes in Ariadne’s house (western wall of room 1). Three probes can be observed: #22, #25 and #26, which remain at 240, 54 and 15 cm from the floor, respectively. Figure 13: Evolution along the year of daily mean parameters: temperature, AH and RH. Data recorded by all probes during the daytime (8:00 AM to 8:00 PM) and night-time (8:00 PM to 8:00 AM). Day 0 corresponds to 24th July 2008 (days <60: summer; 60–151: autumn; 152–239: winter; 240–331: spring). Trajectories were smoothed using a moving average with a weekly window size. Figure 14: Bivariate plot of daily average RH vs. temperature. a) Bivariate plot of daily average RH from each probe with respect to daily average temperature, corresponding to the year 2008–2009 (372 days). b) Theoretical function relating RH and temperature (Equation (2)), which is also depicted inside the bivariate plot. Figure 15: Bivariate plot of daily minimum RH vs. temperature. Bivariate plot of daily minimum RH from each probe vs. daily minimum temperature, averaged for all the 372 days. Horizontal lines in red (45–60%) correspond to the range of RH recommended by the standard DM 10/2001 for the conservation of mural paintings. Figure 16: Bivariate plots (summer vs. winter). a) Bivariate plot of daily maximum temperature (Tmax) averaged for the summer period (7/24/2008 – 9/22/2008) vs. Tmax averaged for the winter period (12/21/2008 – 3/31/2009). b) Bivariate plot of daily minimum RH (RHmin) in summer vs. RHmin in winter. Axes were inverted in the right plot to ease the comparison. Lines in red (45–60%) correspond to the range of RH recommended by the standard DM 10/2001. Figure 17: Position of thermohygrometric probes. Room code as in  Probe #5 was installed at the center of room 3 under a glass box on the ground protecting a mosaic. Probes #6, #8 and #11 were located on the floor level under a ceramic tile that was placed to protect them from accidental stepping. Figure 18: Daily time series of probe #22. Temperature and RH values registered by one specific probe (#22) during a day randomly chosen (February 16th 2009) as well as average values collected by the 26 probes. One measurement was recorded every 30 min. According to the manufacturer, the accuracy is ±0.5°C and ±5% for temperature and RH data-loggers, respectively.
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References
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    • . . . Their names and locations were forgotten until the 18th century when a new interest for antiquity led to excavations 1 . . .
    • . . . The house was built at the end of the second century BC and was heavily damaged during the earthquake of 62 AD, not having been finished its reconstruction on the fateful date of Mount Vesuvius eruption 1 . . .
    • . . . During the following decades, mural frescoes in all rooms that had been left uncovered were seriously damaged due to direct contact with rainwater and the unfavorable thermohygrometric conditions mainly during the summer 1 . . . .
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    • . . . Similar works have monitored the indoor environment in churches, as they contain valuable artifacts 16 17 18 19 20 21 . . .
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    • . . . Similar works have monitored the indoor environment in churches, as they contain valuable artifacts 16 17 18 19 20 21 . . .
    • . . . The fact that RH provides more information than temperatures was also found in a recent study 21 . . . .
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  26. Hygrochron Temperature/Humidity Logger iButton with 8KB Data-Log Memory. Maxim Integrated Products Link Hygrochron Temperature/Humidity Logger iButton with 8KB Data-Log Memory. Maxim Integrated Products , .
    • . . . Each RH data-logger (Datalog Hygrochron DS1923) contains a humidity sensor with an accuracy of ± 5% 26 . . .
    • . . . This range is much lower than the measurement error of ±5% indicated in the manufacturer data sheet 26 . . .
  27. Temperature Logger iButton with 8KB Data-Log Memory. Maxim Integrated Products Link Temperature Logger iButton with 8KB Data-Log Memory. Maxim Integrated Products , .
    • . . . Although this model can also record temperatures, it was decided to use independent devices (Datalog Thermochron DS1922L) for the temperature monitoring 27 , which has the same accuracy (±0.5°C) as DS1923 . . .
    • . . . Next, the mean of both bias estimations was calculated (shown in Table 1) resulting a range from −0.44°C (#18) to +0.53°C (#13), which is consistent with the measurement error of ±0.5°C indicated by the manufacturer 27 . . . .
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    • . . . Knowledge about ideal or limit values of microclimate parameters for conservation of cultural heritage is still poor 28 . . .
  29. UNI 10829Works of Art of Historical Importance. Ambient Conditions for the Conservation. Measurement and AnalysisMilano: UNI Ente Nazionale Italiano di Unificazione1999 Works of Art of Historical Importance. Ambient Conditions for the Conservation. Measurement and Analysis , (1999) .
    • . . . The Italian UNI 10829 29 and DM 10/2001 30 are currently the approved standards on this issue . . .
    • . . . According to 29 , the recommended range of RH and temperature for mural paintings is 55 – 65% and 10 – 24°C, respectively . . .
  30. DM 10/2001Atto di Indirizzo sui Criteri Tecnico-scientifici e Sugli Standard di Funzionamento e Sviluppo dei Musei. Ministero per i Beni e le Attività CulturaliGazzeta Ufficiale della Repubblica Italiana (Official Bulletin of Italian Republica), Rome (Italy)2001DL 112/1998 art. 150 comma 6 Atto di Indirizzo sui Criteri Tecnico-scientifici e Sugli Standard di Funzionamento e Sviluppo dei Musei. Ministero per i Beni e le Attivit&#xE0; Culturali , (2001) .
    • . . . The Italian UNI 10829 29 and DM 10/2001 30 are currently the approved standards on this issue . . .
    • . . . These ranges are narrower than the ones suggested by 30 : 45 – 60% and 6 – 25°C . . .
    • . . . High variability is inappropriate for the conservation of fresco paintings, which encourages some kind of corrective action to reduce the temperature at least in summer 30 . . .
    • . . . According to DM 10/2001 30 , the recommended interval of RH is 45-60% . . .
    • . . . Preliminary results suggest that frescoes in room 2 are better preserved that the rest, which is of interest because room 2 presents ambient conditions closer to the range recommended by DM 10/2001 30 . . .
  31. D Camuffo Microclimate for Cultural Heritage , (1998) .
    • . . . They were calculated using Equation (1) 31 according to RH (%) and temperature (°C). . . .
  32. ASTM E 104–02Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous SolutionsWest Conshohocken, PA: ASTM Intl2012 Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions , (2012) .
    • . . . A further experiment was carried out with aqueous solutions of two salts (lithium chloride and sodium chloride) according to the standard ASTM E 104–02 32 in order to study the measurement errors of RH data-loggers. . . .
  33. Statgraphics Software Link Statgraphics Software , .
    • . . . All ANOVAs were performed using the software Statgraphics 5.1 33 . . . .
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