Nondestructive analyses were performed using portable devices by approaching them to the paintings (Figure 4—image from altarpiece; Figure 5—image from nave dome; Figure 6—image from narthex roof).

FTIR reflectance spectroscopywas performed using a tripod mounted Bruker Alpha II device with a contactless forward looking reflection unit specialized for paintings, spectral domain 400 - 4000 cm⁻¹, resolution 2 cm⁻¹, OPUS /IR software in Windows 10.

Non-destructive X-ray fluorescence elemental analyses (XRF) was performed with a handheld Bruker spectrometer, S1 TITAN series (EDXRF) configured with a Silicon diode PIN detector (SiPIN), Rh target X-ray tube with a maximum voltage of 50 kV.

The samples for destructive analyses were collected from areas where the painting layer was exfoliated in order to not damage the painting.

Destructive FTIR Spectroscopy

FTIR spectra were obtained by employing the well-known KBr pellet technique. The measurements were done with a Jasco FTIR spectrometer in the 4000 to 400 cm⁻¹ spectral domain with a resolution of 4 cm⁻¹.

Gas Chromatography-Mass Spectrometry (GC-MS)

The sample extracts were analyzed with an analytical system (Thermo Electron Corporation) equipped with a Gas Chromatograph (Trace Ultra) coupled with an ion trap mass spectrometer (Polaris Q).

Mass spectrometer experimental conditions were: electron impact 70 eV, ion source temperature 250˚C. Chromatographic separations were achieved on a DB 5 ms (30 m, 0.25 mm i.d.) fused-silica capillary column with a 0.25 μm film dimethysiloxane (5% phenyl groups). The injection was in the mode split less with injector set at 250˚C. As eluent gas helium was used at flow rate 2 mL/min. Oven temperature was programmed from 90˚C (1 min) at 120˚C (0 min) to 10˚C/min and then at 190˚C (0 min) to 3.5˚C/min and then at 4˚C/min to 300˚C (held 20 min).

Sampling procedures: The samples were dissolved in ethanol (Promochem, LGC Standards GmbH, Wesel, Germany) and mixed in an ultrasonic bath two stage of 10 min each maintained at 40˚C. The sample was centrifuged 5 minutes at 3000 rot/min and then 2 µ of supernatant was injected. In this condition the fatty acids were derivatized to ethyl ester fatty acids.

The investigations were performed for each colour from the following paintings.

XRF results from the investigations are shown in Figures 7-17.

From the reflectance spectrum (Figure 18)—one can identify the presence of Prussian blue (2132.75 cm⁻¹), calcium carbonate (1447 cm⁻¹), collagen (1288.18 cm⁻¹ and 712.97 cm⁻¹), egg yolk protein (1541.07 cm⁻¹), gypsum 3403 cm⁻¹, 621 cm⁻¹, spectral domain 4000 - 400 cm⁻¹.

FTIR spectroscopic absorption spectra of red painting material obtained from

the southern and northern wooden walls of the church are presented in Figure 19.

From both destructive and non-destructive FTIR analyses the following materials were identified: ground-gypsum, white chalk, Prussian blue; binder-egg yolk, linseed oil (tempera), animal glue.

Identification of linseed oil in the painting layer by GC-MS coupling

We used a simple GC/MS method for the identification of specific molecular biomarkers of drying oils and lipids used in old art works. Common molecular biomarkers are individual fatty acids. The relative concentration of fatty acids is a very useful indicator for identification of glycerolipids [14] [15] [16]. The procedure was applied for the characterization of two old paint microsamples. The GC/MS chromatogram (TIC) of ethylated palmitic, linoleic, oleic and stearic fatty acids are shown in Figure 20 and their relative concentrations are presented in Table 1.

The quantitative determination of monocarboxylic fatty acids allows us to distinguish between different triglycerides sources (drying oil or egg) on the basis of characteristic parameters [15]. The ability to recognize original materials is due to the use of molecular markers that remain stable under aging.

The unsaturated fatty acids were excluded from classification rules based on previous works [15] that found the ratios of these compounds are dependent on drying and aging conditions. We used the C16:0/C18:0 ratios to discriminate between binders. This parameter is fairly constant for each binder and independent of both the aging treatment and the pigment. This ratio (P/S) can be used to identify each type of drying oil and is not affected by the aging process [14] [15] [16].

From Table 1, it results in that the ratio P/S is 1.02 for Sample 1 and 1.06 for Sample 2. According to the P/S value, it was suggested that linseed oil was used as

a binder. The presence of traces of cholesterol leads to conclusion that small quantity of egg can be also present in the binder material. Our results agree with the results reported earlier.

The compounds detection from the “Agarbiciu green and binder” sample, based on selected ions (Figure 21): (a) m/z 101, palmitic and stearic acids; (b) m/z 301, cholesterol. The detected compounds are specific to vegetable oils and egg yolk.

The digital preservation of the interior of the wooden church will be done using a metadata set that describes the timeline, the physic-chemical composition of the painting layer, detailed photographic documentation and the 3D scanned interior of the church.

Following the physicochemical analyzes described in the previous chapter, the pigments used for the church interior painting can be obtained in the laboratory (Figure 22) digitized and preserved digitally.

The pigments can be used in the process of digital repainting to eliminate the effect of time and other factors that degraded the painting layer (Figure 23).

The documentation of the current preservation status of the painting layer has been made digitally using detailed photography within the visible spectrum, IR and UV (Figure 24).

The photographic documentation was done using professional equipment (Canon 5DSLR, 50 Mpx), the light was measured and recorded every 10 minutes using a spectrometer (Sekonic C7000) (Figure 25), the acquired data will be archived together with the pictures in RAW file format.

The interior has been photographed in 360˚ using an automatic photography system (Giga Pan—Figure 26), the shooting systems enables high resolution photography by combining multiple images of 50 Mpx each with an overlap of 10% - 15%.

A set of HDR image (Figure 27) was obtained using the Z + F 5010X terrestrial laser scanner. This set enables the compositing and tone-mapping of images to extend the dynamic range capability.

To record the exterior conservation status of the wooden church, a UAV was used to inspect the tower and roof structure. Based on the architecture of the wooden churches the exterior of the church tower is hard to inspect with traditional equipment. The church exterior has been recorded with a 4 k camera (Figure 28) to enable the generation of the 3D model.

The interior has been 3D scanned using the Z + F Imager 5010× terrestrial scanner, the model obtained has a resolution of 1 mm, the texture has also been acquired and mapped to the 3D scanned model (Figure 29).

At the following link, all in-situ investigations for the Agârbiciu Wood church can be observed at the following link (https://youtu.be/RDzLErFioX0).