Identifying artefacts

Artefacts are effects observed on the measurement curve that are not directly caused by the sample, that is, effects that have nothing to do with the sample properties you want to measure. 

Buoyancy effects caused by the density of the surrounding gas decreasing on heating. Typically this results in an apparent mass gain of50-200 jxg. Since buoyancy effects are reproducible, the curves can be corrected by performing automatic blank curve subtraction. This also applies to buoyancy effects due to gas switching, a technique often used in TCA. 

Apparent mass gain caused by samples that foam and make contact with the furnace wall. This problem can be overcome by using smaller samples. 

Artefacts can be identified if repeat measurements are made, and blank experiments are performed. 

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The benefit of electrolysis treatment is that the artefact can be cleaned in a uniform fashion, without seeing its original surface harmed. It can let the artefact tell its own tale by revealing surface inscriptions such as the maker s name or stamp, which is the primary element used for authenticating and identifying artefacts. 

Ancient artisans were able to confer special colourings to their artefacts by applying particular techniques and treatments, which were lost in later centuries. They were also able to give copper based alloys the appearance of precious metals. Some of these special methods have been discovered and identified on ancient objects. The most famous of these alloys in Roman times was certainly Corinthian bronze, a copper alloy containing small amounts of precious metals, which acquired a purple-black or blue-black patination... 

Birch bark was also used to produce pitch and tar. The pitch from Betulaceae bark has been found on arrowheads and flint tools from prehistoric ages and the pitch was probably a residue of the original adhesive [92,151,152]. Birch-bark pitch has also been identified in ceramic artefacts as an adhesive to coat, seal, or repair the inner surfaces of the vessels [90]. 

Debromination with ageing has been observed in the indigoid components of purple [171,172], and photochemical breakdown patterns of the three anthocyanidins contained in Arrabidaea chica red dye, produced by Andean Indian cultures in the tenth to fifteenth centuries, have been hypothesized [173]. Although identifying dye sources in ancient artefacts is quite difficult, it is helped considerably by understanding the fading and degradation mechanisms. 

Chapters 3 6 deal with direct mass spectrometric analysis highlighting the suitability of the various techniques in identifying organic materials using only a few micrograms of samples. Due to the intrinsic variability of artefacts produced in different places with more or less specific raw materials and technologies, complex spectra are acquired. Examples of chemometric methods such as principal components analysis (PCA) are thus discussed to extract spectral information for identifying materials. 

Boeda et al. (1996) identified bitumen on a flint scraper and a Levallois flake, discovered in Mousterian levels (about 40 000 BP) at the site of Umm el Tlel in Syria. The occurrence of polyaromatic hydrocarbons such as fluoranthene, pyrene, phenanthrenes and chrysenes suggested that the raw bitumen had been subjected to high temperature. The distribution of the sterane and terpane biomarkers in the bitumen did not correspond to the well-known bitumen occurrences in these areas. In other studies of bitumen associated with a wide variety of artefacts of later date, especially from the 6th Millennium BC onwards, molecular and isotopic methods have proved successful in recognizing different sources of bitumen enabling trade routes to be determined through time (Connan et al., 1992 Connan and Deschesne, 1996 Connan, 1999 Harrell and Lewan, 2002). 

In addition, peak VI (fig. 1) contained two compounds, one identified as lysinoalanine (table 1). Lysinoalanine is a well-known artefact of alkaline protein treatment but is supposed to be formed in dentin by the reaction between a collagen lysine- and a phosphoprotein phosphoserine residue (Fujimoto et al., 1981). Both compounds were not detected by HPLC after FMOC-derivatization, most likely because of fluorescence quenching inherent to the close vicinity of several FMOC groups attached to one molecule. Thus the unknown compound seems rather similar to lysinoalanine. We suggest the unknown compound is histidinoalanine, which is present in dentin (Fujimoto et al., 1982) and likely shows fluo-rence quenching in its FMOC derivate. 

In archaeology, the main purpose of analysis of artefacts is to contribute to a better understanding of the technical development in the remote past and to identify the sources of raw materials and the trade routes. It can also serve as an indirect dating by compositional similitude with well-dated objects. 

In this context, we mention that the ESR spectrum claimed as evidence for the existence of HM-126 + (2A,) [365] was later shown to be an erroneous assignment [366, 367], The presumed seven-line spectrum was shown to be a iuxtaposition of an unknown single-line spectrum plus a six-line spectrum, a doublet of triplets, which was identified as a deprotonation product, 131. Furthermore, the CIDNP evidence for the existence of the 2A, radical cation [361] may also need reevaluation for the reason outlined in Sect. 3.7. Since the assignment was based on different spectra, the possibility of an artefact is hard to eliminate. 

Unfortunately, this synthetic route results in the isolation not of the natural compound CP-263,114 (1), but of the C-7 epimer 15, which proved to be the more stable stereoisomer. The formation of the unwanted C-7 epimer is a consequence of the OSO4-catalyzed dihy-droxylation of intermediate 12, which occurs from the face of the C=C double bond opposite to that desired. Epimerization at C-7 takes place under basic conditions, and on closer inspection it was possible to identify both isomers in the original sample extracted from the fungus [16]. However, the isolation of both isomers could also be an artefact of the extraction process, during which the configuration at C-7 could be partially flipped during treatment with acid and base [2]. 

The first issue identified above has been solved while the other two are presently being addressed. In order to get meaningful experimental data, and to further develop the CuCl/HCl electrolysis reaction, all of these issues need to be resolved. Some of these issues are artefacts of the way in which the electrolysis reaction is being carried out in the laboratory (Issue 1) while others are related more... 

In 1974, Homberg (1974) reported that the action of bleaching earth on cholesterol in solutions of both synthetic triacylglycerol (TAG) and hexane caused the formation of the dehydration product cholesta-3,5-diene. Subsequently it was reported that bleaching of butterfat resulted in the formation of cholesta-3,5-diene (Roderbourg and Kuzdzal-Savoie, 1979) and the authors proposed that the detection of this artefact could be used to identify refined butterfat. In a review article (Kochhar, 1983), it was reported that several other authors had identified steradienes in bleached vegetable oils and proposed that the detection of these could be used to identify refined oils or mixtures of refined and unrefined oil. 

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