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Clicking on the donut icon will load a page at altmetric. Find more information on the Altmetric Attention Score and how the score is calculated. Lead white is known as one of the oldest pigments in art and can be used as a dating material. Upon production following the Stack process, the 14 C isotope of atmospheric carbon dioxide is fixed in the carbonate, and its radiocarbon dating can be used as a proxy for the age of a painting.
Thus, a thermal approach is proposed to separate the various carbonates and isolate the specific 14 C signature to the lead carbonate. In practice, however, discrepancies between the measured radiocarbon ages and expected ages were observed.
FTIR analyses pointed to the formation of metal carboxylates, an indicator that the organic binder is not inert and plays a role in the dating strategy. Upon drying, oxidation and hydrolysis take place leading to the formation of free fatty acids, which in turn interact with the different carbonates upon heating. The proposed procedure was furthermore verified on mixed carbonate-bearing paint samples collected from a Baroque oil painting.
Both projects were led by Professor Dr. Jaap Boon with Dr. Figure 1. Thermogravimetric curves continuous lines and their derivatives dashed lines under nitrogen flow as a function of temperature.
Analysis of various carbonates A in comparison to linseed oil and a paint reconstruction with lead white B. Figure 2. Comparison of different approaches to isolate the 14 C signal of lead white pigment empty squares and paint mockups filled triangles. A Pigment and oil are contemporaneous.
B Paint reconstruction bearing a depleted 14 C lead white mixed in an oil binder carrying an excess of 14 C. Figure 3. Respective FTIR spectra collected after combustion of paint mockup B at different temperatures and for different reaction times.
Full spectrum left with zone of interest highlighted in gray and zoomed-in window between and cm -1 right. Figure 4. Measured radiocarbon ages for a set of paint reconstructions with a defined calcium carbonate to lead white ratio. The empty symbol represents dry powder mixtures, while the filled triangles represent paint reconstructions. Figure 5. Untitled half-length portrait of a young woman wearing a lace bonnet, pearl necklace, and fur-trimmed cape, unsigned, ca.
The previous sampling locations are marked by white boxes, while the new sample sites are indicated in pink. The three details show a close up of the sampling location for samples labeled as P01 white, P02 pink, and P04 brown, respectively B, C, and D.
The scale used represents 5 mm, and the amount of material removed is indicated by the continuous red line. Results of the lead white dating following different procedures E. Subsequent dating of the organic binder from the same sample F. Additional information summarized in four tables and three figures comprise details of reference material and mockup composition, comparison of FTIR spectra following heat treatment, material characterization of samples collected on case study, and respective 14 C results.
This work is part of L. Experimental setup was discussed between L. The ensemble of the results was interpreted and discussed among all authors.
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Lead white is known as one of the oldest pigments in art and can be used as a dating material. Upon production following the Stack process, the 14C isotope of atmospheric carbon dioxide is fixed in the carbonate, and its radiocarbon dating can be used as a proxy for the age of a painting. The previously reported carbonate hydrolysis protocol reaches its limitation when confronted with samples Author: Laura Hendriks, Walter Caseri, Ester S. B Ferreira, Nadim C. Scherrer, Stefan Zumbuhl, Markus Kuffne.
For permission to reproduce, republish and redistribute this material, requesters must process their own requests via the RightsLink permission system. The authors wish to thank Prof. Eglinton for access to GC-MS instrumentation and in particular Negar Haghipour for the support for conducting the analyses.
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More by Laura Hendriks. More by Walter Caseri. More by Ester S. B Ferreira. More by Nadim C. More by Irka Hajdas. More by Lukas Wacker. More by Hans-Arno Synal. Cite this: Anal. ACS AuthorChoice. Article Views Altmetric.
Abstract High Resolution Image. In recent studies, the potential of lead white, a mixture of lead carbonates, cerussite PbCO 3 and hydrocerussite Pb 3 CO 3 2 OH 2as a dating material was pushed forward. The pigment is formed as a white crust on metallic lead as a result of a corrosion process initiated by the combined action of oxygen, carbon dioxide, water vapor, and acetic acid. Details to the reaction chain can be found in the investigation of Gonzalez et al. This left the impression that the approach is relatively straightforward and thus applicable to a much broader spectrum of paintings.
Lead white was a commonly used pigment and thus not the most expensive, but nonetheless, it was economically advantageous to cut the pigment with some filler or extender. The search for greater whiteness was further explored by the addition of pigmented additives, such as vermilion or smalt to counteract the yellowness of the pigment.
In the presence of other carbonates, the accuracy of the results is impaired. Indeed, other carbonate minerals generally carry depleted 14 C carbonate anions, which means that dead carbon i. The proposed acidic approach to radiocarbon date lead white therefore reaches its limitation in the presence of other carbonates.
Furthermore, the necessity of taking a sample adds to the challenge. Again, in the initial study, a sample of pure lead white was sought, which required sampling in the center of the pictorial layer.
Although the sample was collected in a pre-existing paint crack, such a central sampling location will not be permitted on conservation ethical grounds; minimal invasive sampling along canvas edges is preferable.
In her work, Stols-Witlox reviewed the terminology of preparatory layers in oil paintings between toand she described multiple formulations with chalk, lead white, and even pigment-based formulations mixed in various binding media such as oil, glue, starch, or casein. Hence, a selective separation strategy of the different carbonates is necessary.
Although chemically alike, mineral carbonates can be separated based on their physical properties, i. Upon heating, the carbonates will dissociate and release carbon dioxide under formation of the corresponding metal oxide.
Thus, in this study, a methodical investigation regarding the selective separation of lead white from a paint sample for further radiocarbon analysis is reported. In combination with Fourier transform infrared spectroscopy FTIRthermogravimetric analysis TGAand gas-chromatography mass spectrometry GC-MSthe process was studied in depth, hereby providing an overview of the thermal separation approach for lead white paint dating and the encountered challenges, as well as its limitations.
Experimental Section. The unattributed half-length female portrait previously dated by 14 C analysis of the lead white-bearing paint, 2 shown in Figure 5 A, was further investigated since the lead white-bearing paint identified was impure and mixed with other carbonates on the painting edge, which is a more favorable sampling location.
This oil on canvas is unsigned and undated, although stylistic assessment suggests a late 17th to a beginning 18th century date, which is supported by 14 C analysis of the canvas, binder, and lead white. A series of oil mockups with known compositions were examined. Detailed information to the mockups can be found in Table S-1 in the Supporting Information.
FTIR spectra of all samples were collected prior and after the different thermal treatments in order to qualitatively monitor changes in species.
Acquisition parameters covered a spectral range from to cm -1 with a resolution of 16 cm -1 at scans. Helium was used as the carrier gas at a constant flow of 1.
Results and Discussion. Thermogravimetric analyses of pure carbonates display distinct decomposition temperatures Figure 1as expected. In particular, the reaction is complete within the first 15 min. This data shows that in contrary to the work of Beck et al. High Resolution Image.
The thermal behavior of lead white in an oil medium is quite different as already observed by Bonaduce et al. On the basis of the peak position, shape, and temperature, the presence of both fatty acids as well as lead carboxylate can be inferred.
As shown in Figure 2 A, the obtained 14 C age of lead white pigment empty squares and paint filled triangles is unaffected by the sample preparation and delivers consistent ages. While the hydrolysis approach is material specific and independent of any other carbon source, the thermal approach presents the disadvantage that a small percentage of the organic binder also reacts along the decomposition of the lead carbonate and this despite the absence of an oxidizing agent CuO.
New chemical analysis allows for less invasive dating of artwork Carbon dating of lead white paint from canvas edges could help uncover forgeries by Benjamin Plackett, special to C&EN. American Chemical Society: Chemistry for Life. Dedicated at the University of Chicago on October 10, In , Willard Libby proposed an innovative method for dating organic materials by measuring their content of carbon, a newly discovered radioactive isotope of carbon. The Ins and Outs of 14C Dating Lead White Paint for Artworks Application Laura Hendriks,* Walter Caseri, Ester S. B Ferreira, Nadim C. Scherrer, Stefan Zumbuhl, Markus Ku?ner, Irka Hajdas, Lukas Wacker, Hans-Arno Synal, and Detlef Gunther.
The extent of the binder contribution was addressed by dating the Bleiweiss-Schoonhoven sample, which contains 14 C-depleted lead white in a 14 C-rich oil medium nuclear bomb test signal. As a result, the 14 C age is a mixed signal of both sources yielding a 14 C age in the range from to 15, yrs BP.
In comparison to previously published data of 20, yrs BP, an offset is observed; nonetheless, the distinct signature of depleted 14 C material is still noticeable. Depending on the respective reaction time, the oil contribution varies.
Under the assumption that the pigment and the organic binder are from the same time period, the oil contribution is not considered to interfere with the lead white dating. Another point to highlight is the absence of isotopic fractionation during sample preparation, which is critical for 14 C measurements as the relative enrichment or depletion of 14 C with respect to 12 C will cause an age bias.
The paint reconstructions prepared with linseed oil modern at varying ratios of lead carbonate modern, Stack process to calcium carbonate radiocarbon dead delivered contradicting results.
Surprisingly, an unexpected trend toward older ages was observed. In particular, the higher the calcium carbonate content was, the older the age was, thus indicating that the 14 C-depleted calcium carbonate also reacted in some manner.
This one is typically composed of triglyceride esters of polyunsaturated fatty acids.
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Partial hydrolysis generates glycerol and free fatty acids, which are potential candidates to react with the carbonate present. A deeper understanding of the species formed was brought through FTIR analysis. The dominant change in all spectra at some point is the loss of intensity of ester bands at, and cm -1respectively, which is characteristic for drying oil. Indeed lead white, which contains both lead carbonate and lead hydroxide moieties, is not only used by artists for its white color but also because of its excellent drying capabilities.
By drawing electron density from carbonyl groups, a destabilization occurs which promotes ester hydrolysis.
The combined action of heat therefore plays an additional important role. Sample D composed mostly of calcium carbonate takes much longer to react as little lead white is present. Moreover, it is known that the heating of esters in a moisture-free system can also lead to the formation of free fatty acids. However, although in the collected FTIR spectra the characteristic bands for esters all disappear at some point, no carboxylic acid formation is recorded, which would be expected as a result of the hydrolysis of a drying oil polymeric network typically leading to the formation of diacids, glycerols, aldehydes, ketones, and possibly some cross-linked moieties with multiple acid groups.
Generally, a broadening of the carbonyl band between and cm -1 is observed, which suggests that the hydrolysis products have actually reacted further with metal ions to form metal carboxylates. Extensive work within the MOLART and De Mayerne research programs provided the first results in characterizing saponification processes in this context.
Generally, an absorption band between and cm -1 is attributed to carboxylate vibrations. The exact frequency depends on the coordinated metal. A clear identification is not always straightforward due to the shape of the bands. As a result of metal carboxylate formation, the binding media can be described as an ionomer-like system, within which the coordination of the metal ion is not always well defined and causes a broadening of the IR band.
In the present case, the indication of metal soap formation within the network is well visible in sample B ratio in Figure 3. Upon heating, a shoulder appears around cm -1which can be attributed to lead carboxylates. Most likely these species are already being formed at lower temperatures in all samples, but due to overlaps with neighboring Pb carboxylates and the broad carbonate band, these are not always visible. Such little amounts are difficult to identify using FTIR spectroscopy due to overlap with neighboring bands.
This shift is somewhat surprising but can be explained by the thermal behavior of lead white paint. In their study, Bonaduce et al.
In order to investigate this phenomenon further, a paint reconstruction containing only calcium carbonate in linseed oil was prepared, following the same experimental conditions. An offset was nonetheless observed, indicating that acidic moieties reacted with the calcium carbonate. This result is explained by standard ester hydrolysis which is linked to the oil drying processes. The presence of lead only promotes this reaction, thus increasing the formation of free fatty acids.
This observation is consistent with the review by Noble, who states that the time frame for soap formation depends on the availability of fatty acids.
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The cations react immediately with the acids present in the organic binder and form carboxylates, such as lead stearate, which are then very stable under the measuring conditions and no longer evaporate. In the case of a pure lead white paint layer, the acids have no negative effect on the thermal decomposition and respective carboxylate formation.
However, in the case of mixtures of carbonates, i. With increasing CaCO 3 content, the availability of lead oxide that can bind the acids decreases. The excess acids are therefore free to react with the calcium carbonate, hereby promoting its decomposition and the liberation of depleted 14 CO 2which is an undesired negative effect. By exposing oil paints to an organic solvent, soluble organic components from the paint film can be extracted, in particular, lower molar mass free acids.
The test samples were therefore immersed in either dichloromethane DCMacetone, or ethanol prior to the thermal treatment step Figure 4. After immersion for 24 h, the collected FTIR spectra all displayed similar features, namely, a general loss of intensity for the oil bands see Figure S-2 in SI.
When comparing the spectra after combustion, the aforementioned metal carboxylate bands are no longer visible. The introduction of a solvent extraction step is hereby beneficial in removing free fatty acids and limiting their subsequent availability in future saponification reactions induced through the heating step.
To validate the proposed strategy for lead white dating, the nature of the extracted material, i.
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After evaporation of the solvent, the FTIR spectrum of the extract shows a broad carbonyl band at cm -1 as well as a shoulder at cm -1which indicates that the mobile material is more degraded see Figure S-2 in the SI. Either hydrolysis or oxidative fragmentation reactions produce acids, which are not necessarily free fatty acids, but are often still bound to glyceride residues.
Their presence within the paint matrix as mobile fraction would explain the observed biased 14 C age, as they can react with the carbonates and form metal carboxylates, hereby liberating CO 2. As the oil dries, a complex mixture of fatty acids, glycerol, and glyceride esters as well as partially cross-linked low molecular weight compounds are produced, which are all susceptible to removal by solvent extraction.
The exact proportions may vary in function of the paint composition, its curing state, and the solvent extraction exposure time. Complementary preliminary GC-MS analysis of the solvent extracts indicates the presence of fatty acids derived from the linseed oil binder.
The wash extract exhibits free fatty acids, in particular, palmitic and stearic acid, with lower amounts of nonanoic and octanoic acids. Smaller portions of unsaturated fatty acids oleic as well as dicarboxylic acid azelaic were also found to be washed out by the solvent. These observations corroborate the production of free fatty acids through the drying reaction and hydrolysis induced by the pigment. These in turn react with the metal carbonates present in the paint and as such are the source of the misleading older ages.
The choice of the solvent could be further investigated as the mentioned acids are best soluble in cyclic, aprotic solvents. In the case of older objects, this negative effect is not expected to be as pronounced as in the model paints. Investigations of 50 year old paint models showed that lead white paint undergoes a net decrease in its ester bands upon drying, and the available fatty acids have since long formed metal soaps.
As a result, an increased stabilization of the paint film is observed, and the amount of extractable material, i. Lead compounds are known to trigger many reactions within a paint layer but their respective reactivity in various situations must still be evaluated, such as the effect of postsynthesis treatment of lead white, changes in the hydrocerussite to cerussite ratio due to pH, or the formation of other species.
In the case of the half-length female portrait, three samples with varying carbonate contents were compared against the previous published data. In the thermal approach, the age offset was reduced to several hundreds of years, i. Although metal carboxylates cm -1 are observed in all samples, the triglyceride network is not yet fully cross-linked, and acid functional groups cm -1 are still visible. The successive extraction in acetone and ethanol prior to the combustion resolved the issue as demonstrated in Figure 5 E.
Moreover, following the dating of the lead white, the remaining sample material was further treated with HCl 1 M for subsequent dating of the organic binder. As displayed in Figure 5 F, the dating of the binder is much more robust.
Owing to variations in atmospheric 14 CO 2 over time, the measured 14 C ages require calibration to calendar ages, which for the previously determined mean value extends from the midth to midth century AD and fits the art historical assessment as already reported in Hendriks et al.
These results conducted on aged sample material put the proposed strategy in a more practical context. The altered chemistry of the oil paint is more representative of museum objects, as compared to relatively young model paints.
The gathered data suggests that the free acid moieties accelerate the carbonate decomposition and hereby liberate carbon dioxide with different 14 C signatures. The state of binding media oxidation and polymerization has therefore a critical influence on the 14 C dating step for mixtures of carbonates, i. Strong negative effects on the measured 14 C ages may be observed if the availability of acids is larger than the formed lead oxide and therefore promote the decomposition of calcium carbonate too.
The prepared paint mockups however do not reflect the altered chemistry of aged oil, where the negative acid effect is expected to be less pronounced as the organic binder has already undergone extensive hydrolysis reactions followed by polymerization.
The sample characterization by FTIR spectroscopy is hereby crucial for establishing the state of oil oxidation by identifying the presence of esters, acids, or metal carboxylates as well as the relative carbonate content.
FTIR analyses are essential in evaluating the reliability of the results. In this work, the introduction of a solvent extraction step prior to combustion is proposed as a strategy to limit the negative acid effect and shows to have a positive influence. Moreover, this approach presents the added benefit of removing potential conservation products and should therefore be included as the default step in the sample preparation procedure.
The proposed strategy displays enormous potential in the dating of the lead white pigment as the interfering actors have been identified, i. These are naturally deactivated through the formation of carboxylates as the paint film ages but can also be actively eliminated by solvent extraction.
As a result, no 14 C age bias is expected. When targeting new dating materials within the pictorial layer, a combination of analytical techniques is essential to gain a deeper comprehensive understanding of the paint material, which will then allow to develop a reliable dating strategy. Only in this way can scientifically educated sampling take place and hereby ensure a meaningful result from the radiocarbon analysis.
Supporting Information. Author Contributions This work is part of L. This research was supported by an ETH Grant 21 The authors declare no competing financial interest.
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Absolute dating of lead carbonates in ancient cosmetics by radiocarbon. Selective dating of paint components: Radiocarbon dating of lead white pigment. Cambridge University Press. Lead white is a man-made white pigment commonly used in works of art.
In this study, the possibility of radiocarbon dating lead white pigments alone and in oil paints was explored using well-dated lead white pigments and paints.
Resulting 14C ages on lead white pigments produced following the traditional stack process, where carbonate groups results from the incorporation of CO2 originating from fermn. The method was applied to two case studies, where lead carbonate samples were dated in two oil paintings, one Baroque and one from the 20th century.
We hereby show that the lead white pigment can be dated by 14C and used as proxy for the time of creation of an artwork. A single lead white paint sample can yield two distinct radiocarbon ages, one from the carbonate and one from the natural org.
This study thus proposes new strategies for 14C dating of artworks. Synthesizing lead white pigments by lead corrosion: New insights into the ancient manufacturing processes. Elsevier Ltd. Traditional "stack "manufg. Global reaction scheme is revealed, along with stratification of corrosion products with CO2 gradient, leading to flakiness of corrosion layer.
Kinetic and epitaxial features rule the polyphased structure, explaining hydrocerussite-rich compns. Microstructure of cerussite appears as a differentiation criterion between stack-made and industrial pptn. Particular conditions reported in ancient writings are tested and discussed to understand unusual processes. Google Scholar There is no corresponding record for this reference. Farbenlexicon ; Halle Elsevier B. Fifteen lead white-contg.
XRD beamline ID The Rietveld anal. This first insight into a still widely unknown domain gives some hints, but also raises questions about the artists' preferences for selecting, prepg. A significant increase of the crystallites size over five centuries also suggests an evolution of these processes. Direct measurements of small 14C samples after oxidation in quartz tubes.
Methods Phys. Fahrni, S. Small 14C samples gain importance in environmental research and for dating purposes.
However, throughput of such samples is limited by the prepn. In the authors' approach, oxidn. As combustion byproducts probably interfere with ionization processes in the gas ion source, the authors addnl. Developments in accelerator mass spectrometry. Mass Spectrom. A review. This report attempts to summarize the tech. The related impact of the AMS measurement technol. The accompanying article by W.
Kutschera overviews these applications. Here, the author is providing an introduction to the basics principles of AMS measurement technol. A retrospective view is given on the major development steps of AMS instruments and measurement technique. Special attention is paid to the simplification of AMS systems by reducing their size and complexity. These developments have launched the wide spread use of AMS in modern research fields.
Today, com. There are a no. Consequently, the latest developments in radiocarbon AMS are summarized. A novel tabletop AMS system with overall dimensions of only 2. The new system is now fully operational. A detailed description of the system is given and results of performance tests are discussed. Samples taken from the edges of a canvas, though, often contain other carbonates found in different colored pigments or in paint fillers such as chalk, which can muddle the results.
To get around the multiple carbonate problem, Hendriks decided to incinerate her samples and collect the resulting carbon dioxide for radiocarbon dating. It turned out that the paint in the fresh samples had more fatty acids from the oil in the paint, which dissipate as they age and react with other substances. These fatty acids interact with the carbonates during heating, distorting the data. Hendriks found that the solution was to remove the fatty acids via solvent extraction before burning.
By doing that, she was able to validate the method for both the old and new samples. Including the solvent extraction step is important even with samples from old paintings because a painting may have undergone undocumented conservation treatment. Materials added during a restoration could have different carbon contents, Hendriks says. Converting the level of carbon measured into an actual year requires consulting a calibration chart of known historical atmospheric concentrations.
For older paintings, it may only be possible to estimate age to within a few decades because CO 2 levels did not change as quickly then and so are less distinct. The power is now in your nitrile gloved hands Sign up for a free account to increase your articles.
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