Academia.eduAcademia.edu

Figure 2 – uploaded by Irene Pieralli

See full PDFdownloadDownload figure
Table 2. Number of samples varnished. 2.2.3. Painted Mock-ups for Extraction Tests

Table 2 Number of samples varnished. 2.2.3. Painted Mock-ups for Extraction Tests

Related Figures (13)

Table 1. Composition of varnish formulations A (traditional) and B (alternative).
Table 1. Composition of varnish formulations A (traditional) and B (alternative).
Figure 1. Pre-varnished mock-ups (5 cm x 3 cm): (a) cerulean blue; (b) ivory black; (c) zinc white; and (d) rutile. The samples were labelled with a letter (C-cerulean blue, A-ivory black, Z-zinc white, T-rutile) and a sequential number to identify them. Figure 1. Pre-varnished mock-ups (5 cm x 3 cm): (a) cerulean blue; (b) ivory black; (c) zinc white; (Figure 1; Table 2). The canvas support board substrate consisted of cardboard covered by a fine canvas frame of pure cotton (100%) with a dolomite preparation and an acrylic binder. Varnish layers without pigments were applied on glass slides to investigate the behaviour of formulations A and B with and without pigments (Table 2).
Figure 1. Pre-varnished mock-ups (5 cm x 3 cm): (a) cerulean blue; (b) ivory black; (c) zinc white; and (d) rutile. The samples were labelled with a letter (C-cerulean blue, A-ivory black, Z-zinc white, T-rutile) and a sequential number to identify them. Figure 1. Pre-varnished mock-ups (5 cm x 3 cm): (a) cerulean blue; (b) ivory black; (c) zinc white; (Figure 1; Table 2). The canvas support board substrate consisted of cardboard covered by a fine canvas frame of pure cotton (100%) with a dolomite preparation and an acrylic binder. Varnish layers without pigments were applied on glass slides to investigate the behaviour of formulations A and B with and without pigments (Table 2).
Table 3. Absorption bands and chemical shifts obtained for the varnish ingredients and pigments. In addition, preliminary extraction tests were performed to verify the possibility of extraction of paint components by the solvent mixtures used for the two formulations. The tests were performed by soaking, for short (10 min) and long (24 h) time fragments of egg yolk film, egg tempera paint (yolk only) pigmented with ivory black, and linseed oil paint pigmented with rutile in the two different solvent mixtures, A and B, used to obtain the traditional and alternative formulations, respectively. For these preliminary extraction tests, available films with adequate natural ageing samples (containing ivory black with egg yolk and titanium rutile white for linseed oil) were used.
Table 3. Absorption bands and chemical shifts obtained for the varnish ingredients and pigments. In addition, preliminary extraction tests were performed to verify the possibility of extraction of paint components by the solvent mixtures used for the two formulations. The tests were performed by soaking, for short (10 min) and long (24 h) time fragments of egg yolk film, egg tempera paint (yolk only) pigmented with ivory black, and linseed oil paint pigmented with rutile in the two different solvent mixtures, A and B, used to obtain the traditional and alternative formulations, respectively. For these preliminary extraction tests, available films with adequate natural ageing samples (containing ivory black with egg yolk and titanium rutile white for linseed oil) were used.
1 egs = ege yolk without pigment, black = egg yolk with ivory black, white = oil with rutile; * percentage relative to the dry weight (mg) of the extracted sample (mg). Table 4. Extraction tests.
1 egs = ege yolk without pigment, black = egg yolk with ivory black, white = oil with rutile; * percentage relative to the dry weight (mg) of the extracted sample (mg). Table 4. Extraction tests.
Figure 2. Extraction carried out on egg yolk with ivory black paint layers: (a) with solvent mixture of formulation A for 24 h; (b) with solvent mixture of formulation B for 24 h.
Figure 2. Extraction carried out on egg yolk with ivory black paint layers: (a) with solvent mixture of formulation A for 24 h; (b) with solvent mixture of formulation B for 24 h.
Figure 3. RGB and UVL images of varnished mock-ups and glass slides with A formulation (a,c with B formulation (b,d), respectively. The varnish formulations were applied by brush. Consequently, the varnish films were not flat but wavy and without a uniform thickness, as evinced by UVL (Figure 3).
Figure 3. RGB and UVL images of varnished mock-ups and glass slides with A formulation (a,c with B formulation (b,d), respectively. The varnish formulations were applied by brush. Consequently, the varnish films were not flat but wavy and without a uniform thickness, as evinced by UVL (Figure 3).
Table 5. Colorimetric variation of the samples. Tj: unvarnished samples; To: varnished samples Ty: after natural aging; T2: after artificial aging. C: cerulean blue; A: ivory black; Z: zinc white; T titanium white; v: glass slide. There are a number of studies that have looked at appearance effects due to the application of varnish films on paint layers [21—25,33]. Among them, the study by Simonot and Elias concludes that firstly the varnish layer induces a levelling of the paint layer, which results in an increase in specular reflected light and gloss [34,35]. Added to this is a decrease in diffuse reflectance due to the weak absorption of the varnish layer. The result, the authors argue, is a darkening and desaturation of the final paint surface the lighter and more saturated the initial paint film (and the thicker the varnish layer).
Table 5. Colorimetric variation of the samples. Tj: unvarnished samples; To: varnished samples Ty: after natural aging; T2: after artificial aging. C: cerulean blue; A: ivory black; Z: zinc white; T titanium white; v: glass slide. There are a number of studies that have looked at appearance effects due to the application of varnish films on paint layers [21—25,33]. Among them, the study by Simonot and Elias concludes that firstly the varnish layer induces a levelling of the paint layer, which results in an increase in specular reflected light and gloss [34,35]. Added to this is a decrease in diffuse reflectance due to the weak absorption of the varnish layer. The result, the authors argue, is a darkening and desaturation of the final paint surface the lighter and more saturated the initial paint film (and the thicker the varnish layer).
application of the thick layer of varnish (Tg) (Figure 4a,b). From their spectra, it is clearly visible that the Ti spectra in the UV-blue region show different trends compared to those of the same samples acquired at To. These differences are largely due to the curing processes of the paint film and partly to the presence of the superficial varnish film, which was very thick. In the case of the varnished zinc white mock-ups, this fact resulted in a reduction of the yellow component manifested in both the SCI and SCE measurements. For cerulean blue mock-ups, instead, the effect of the varnish is more evident in the SCE configuration since, in addition to a marked variation in b* (it tends to increase the perception of blue), and there is a perceptible decrease in brightness L*. Differently from what is reported by Simonon and Elias, in this case C* tends to increase with the presence of the varnish film. The case of one of the two ivory black mock-ups (A2) deserves attention since a very different behaviour of L* was found between the two measurement configurations. In fact, once painted (To) the lightness value changes a lot (AL* = 12.05) compared to before (Tj) but only the value obtained with the SCE configuration. This fact can be explained by looking at the spectra (Figure 4c) in which it is evident that the varnish has considerably reduced the reflectance (SCE) over the entire visible range (as reported by Simonot and Elias). This effect is more perceived by the measure in which the specular component (SCI) is present as the new paint film is extremely smooth with a strong gloss component that results in a more intense reflectance. Figure 4. SCI and SCE reflectance spectra for zinc white (a), cerulean blue (b), and ivory black (c) mock-ups for Ti, TO, and T2. For zinc white and cerulean blue, the SCI and SCE spectra following Ti and before TO where complete curing of the two paint films had been achieved are also shown.
application of the thick layer of varnish (Tg) (Figure 4a,b). From their spectra, it is clearly visible that the Ti spectra in the UV-blue region show different trends compared to those of the same samples acquired at To. These differences are largely due to the curing processes of the paint film and partly to the presence of the superficial varnish film, which was very thick. In the case of the varnished zinc white mock-ups, this fact resulted in a reduction of the yellow component manifested in both the SCI and SCE measurements. For cerulean blue mock-ups, instead, the effect of the varnish is more evident in the SCE configuration since, in addition to a marked variation in b* (it tends to increase the perception of blue), and there is a perceptible decrease in brightness L*. Differently from what is reported by Simonon and Elias, in this case C* tends to increase with the presence of the varnish film. The case of one of the two ivory black mock-ups (A2) deserves attention since a very different behaviour of L* was found between the two measurement configurations. In fact, once painted (To) the lightness value changes a lot (AL* = 12.05) compared to before (Tj) but only the value obtained with the SCE configuration. This fact can be explained by looking at the spectra (Figure 4c) in which it is evident that the varnish has considerably reduced the reflectance (SCE) over the entire visible range (as reported by Simonot and Elias). This effect is more perceived by the measure in which the specular component (SCI) is present as the new paint film is extremely smooth with a strong gloss component that results in a more intense reflectance. Figure 4. SCI and SCE reflectance spectra for zinc white (a), cerulean blue (b), and ivory black (c) mock-ups for Ti, TO, and T2. For zinc white and cerulean blue, the SCI and SCE spectra following Ti and before TO where complete curing of the two paint films had been achieved are also shown.
TR FT-IR spectra of varnished glass slides and paint samples showed all the charac- teristic absorption bands of the Laropal® A81. No bands attributable to the underlying paint layer were detectable, probably because they are hidden by the varnish signals. As an example, the TR FT-IR spectra of the zinc white paint sample uncoated, with formulation A and with formulation B, are shown in Figure 5. Figure 5. TR FT-IR spectrum of the zinc white mock-up uncoated (left), with formulation A (up right) and with formulation B (down right).
TR FT-IR spectra of varnished glass slides and paint samples showed all the charac- teristic absorption bands of the Laropal® A81. No bands attributable to the underlying paint layer were detectable, probably because they are hidden by the varnish signals. As an example, the TR FT-IR spectra of the zinc white paint sample uncoated, with formulation A and with formulation B, are shown in Figure 5. Figure 5. TR FT-IR spectrum of the zinc white mock-up uncoated (left), with formulation A (up right) and with formulation B (down right).
Figure 6. TR FT-IR spectra of a mock-up with titanium white pigment rutile unvarnished (Tj), with formulation B (To), and after artificial ageing (Tz) in two different locations where the varnish layer has a different thickness due to artificial ageing. Figure 6. TR FT-IR spectra of a mock-up with titanium white pigment rutile unvarnished (Tj), with A relatively good preservation of the varnish layer was also observed for the artificially aged titanium white paint samples. As with the zinc white mock-ups, a reduction in the yellow values (b*) towards the neutrality was detected with a non-perceptible colour variation (AEgg < 2). Laropal® A81 absorption bands were still clearly visible in the IR spectra, although, in some cases, they appeared to have a lower relative intensity because the characteristic bands of the titanium white pigment became more prominent (Figure 6). These data could be related to a thinning of the varnish film, as reported in other papers for Laropal® A81 on silicon wafers, quartz, and simple glass slides [36,37].
Figure 6. TR FT-IR spectra of a mock-up with titanium white pigment rutile unvarnished (Tj), with formulation B (To), and after artificial ageing (Tz) in two different locations where the varnish layer has a different thickness due to artificial ageing. Figure 6. TR FT-IR spectra of a mock-up with titanium white pigment rutile unvarnished (Tj), with A relatively good preservation of the varnish layer was also observed for the artificially aged titanium white paint samples. As with the zinc white mock-ups, a reduction in the yellow values (b*) towards the neutrality was detected with a non-perceptible colour variation (AEgg < 2). Laropal® A81 absorption bands were still clearly visible in the IR spectra, although, in some cases, they appeared to have a lower relative intensity because the characteristic bands of the titanium white pigment became more prominent (Figure 6). These data could be related to a thinning of the varnish film, as reported in other papers for Laropal® A81 on silicon wafers, quartz, and simple glass slides [36,37].
Figure 7. T FT-IR spectrum of a sample of the mock-ups with cerulean blue and formulation B after accelerated ageing: (a) taken from an area with varnish (bands due to the Laropal® A81 are still detectable); (b) taken from an area with small varnish residues (only very low signals attributable to Laropal® A8lare detectable, while bands due to calcite of the substrate and pigment have become dominant). The TR FT-IR and T FT-IR spectra collected from the blue and black mock-ups dis- played no structural changes in the varnish or alteration products. However, they showed a less homogeneous distribution of both traditional and alternative varnishes after ageing, as the absorption bands of the resin show highly variable intensities depending on the areas analysed. This could be attributed to a decrease in its thickness in some areas caused by ageing in the climate chamber (Figure 7).
Figure 7. T FT-IR spectrum of a sample of the mock-ups with cerulean blue and formulation B after accelerated ageing: (a) taken from an area with varnish (bands due to the Laropal® A81 are still detectable); (b) taken from an area with small varnish residues (only very low signals attributable to Laropal® A8lare detectable, while bands due to calcite of the substrate and pigment have become dominant). The TR FT-IR and T FT-IR spectra collected from the blue and black mock-ups dis- played no structural changes in the varnish or alteration products. However, they showed a less homogeneous distribution of both traditional and alternative varnishes after ageing, as the absorption bands of the resin show highly variable intensities depending on the areas analysed. This could be attributed to a decrease in its thickness in some areas caused by ageing in the climate chamber (Figure 7).
Figure 8. (a) 'H-NMR spectrum of the extract from mock-ups with ivory black and formulation A at T>. (b) ‘H-NMR spectrum of Tinuvin® 292. (c) 'H-NMR spectrum of film obtained from formulation A before ageing. * Tinuvin® 292 signals.
Figure 8. (a) 'H-NMR spectrum of the extract from mock-ups with ivory black and formulation A at T>. (b) ‘H-NMR spectrum of Tinuvin® 292. (c) 'H-NMR spectrum of film obtained from formulation A before ageing. * Tinuvin® 292 signals.
Observing the UV-Vis spectral trends of the mock-ups (Figure 9), one can infer that the film-forming materials applied to the glass slides transmitted the incident radiation without any absorption. As far as mo the UV component while reflecting t ck-ups are concerned, both white mock-ups absorbed he visible one; those with cerulean blue absorbed the UV radiation and that in the 530-680 nm range; the black samples have absorbed all the incident radiation emitted by the SO of the incident radiation by the dar LARBOX 3000e. It follows that the greater absorption ker mock-ups could have induced a photochemical degradation and an increase in the temperature of the paint film surface that, in turn, would have increased the temperature of the varnish. Figure 9. UV-Vis-NIR spectra of the painted layers without varnish. Blue line—Cerulean blue, black line—ivory black, green line—zinc white, and red line—rutile.
Observing the UV-Vis spectral trends of the mock-ups (Figure 9), one can infer that the film-forming materials applied to the glass slides transmitted the incident radiation without any absorption. As far as mo the UV component while reflecting t ck-ups are concerned, both white mock-ups absorbed he visible one; those with cerulean blue absorbed the UV radiation and that in the 530-680 nm range; the black samples have absorbed all the incident radiation emitted by the SO of the incident radiation by the dar LARBOX 3000e. It follows that the greater absorption ker mock-ups could have induced a photochemical degradation and an increase in the temperature of the paint film surface that, in turn, would have increased the temperature of the varnish. Figure 9. UV-Vis-NIR spectra of the painted layers without varnish. Blue line—Cerulean blue, black line—ivory black, green line—zinc white, and red line—rutile.
Related topics:
PaintingConservation of Easel PaintingsConservator Restorer
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved