Metal artifacts production

Mechanisms regulating deterioration processes in the burial state are still rather unknown and little research has been done on the consequences of long-term corrosion on the stability of the objects. Nevertheless, some studies have been performed on metal artifacts, seeking to characterize the surface layer as well as establish a relationship between the composition of the corrosion products and the environment where they formed. 

MacLeod ID (1991) Identification of corrosion products on non-ferrous metal artifacts recovered from shipwrecks. Stud Conserv 36 222-234. 

STUDY AND RECONSTRUCTION OF EARLY CULTURES usually rely upOU whatever evidence can be recovered from their archaeological contexts. Pottery, stone, and metal artifacts often form the basis for the knowledge of how people lived and worked in the past. Textile fabric products, however, function in much closer associations with people than do the more durable implements. As a result, these products contain valuable information about those who produced, used, and ultimately discarded them. Nevertheless, except in a few rather well-known cases, textile fabrics do not survive the vicissitudes of environmental conditions that follow the final textile use and encourage decay. 

Apart from the application of XPS in catalysis, the study of corrosion mechanisms and corrosion products is a major area of application. Special attention must be devoted to artifacts arising from X-ray irradiation. For example, reduction of metal oxides (e. g. CuO -> CU2O) can occur, loosely bound water or hydrates can be desorbed in the spectrometer vacuum, and hydroxides can decompose. Thorough investigations are supported by other surface-analytical and/or microscopic techniques, e.g. AFM, which is becoming increasingly important. 

The Production Department was not amused, because lower values had been expected. Quality Control was blamed for using an insensitive, unse-lective, and imprecise test, and thereby unnecessarily frightening top management. This outcome had been anticipated, and a better method, namely polarography, was already being set up. The same samples were run, this time in duplicate, with much the same results. A relative confidence interval of 25% was assumed. Because of increased specificity, there were now less doubts as to the amounts of this particular heavy metal that were actually present. To rule out artifacts, the four samples were sent to outside laboratories to do repeat tests with different methods X-ray fluorescence (XRFi °) and inductively coupled plasma spectrometry (ICP). The confidence limits were determined to be 10% resp. 3%. Figure 4.23 summarizes the results. Because each method has its own specificity pattern, and is subject to intrinsic artifacts, a direct statistical comparison cannot be performed without first correcting the apparent concentrations in order to obtain presumably true... 

Archaeological artifacts are considered to be objects that have been buried for very long periods of time—sometimes many centuries or even millenaries. After such long periods, they are deeply modified, consisting of mostly a mixture of metallic remnants and mineral products, which sometimes hinders their identification (Fig. 5.2). 

During the long burial period, extended redistribution of material has taken place. While metal went outwards, ions like chloride and impurities from the environment diffused inwards, resulting in a mass of corrosion products that occupies a volume approximately double the initial size. As a consequence, part of the artifact remains... 

In any manner, even though some of the classical corrosion forms can be also found in archaeological finds, fhey are frequently configured in a very complex form—either from a morphological, structural, or chemical viewpoint. Moreover, corrosion products bear a large piece of information about the artifact s life and should not be inadvertently removed, contrarily to modern metals, which would simply be etched. It is a big challenge to conserve such objects. On the one hand, it... 

A cleaning treatment used to be applied to artifacts with a good metallic structure, whose surface is generally covered with a thin layer consisting in a mixture of corrosion products and grime, sometimes called tarnish. Cleaning aims to remove this undesired superficial layer, without (or with minimal) loss of the metallic substrate. In many cases, such a goal is more easily achieved by electrochemical methods than by mechanical and chemical methods [282]. 

The galvanic or contact method was the precursor to electrochemical treatment [283]. In an electrolytically conducting solution, the artifact is brought into contact with a piece of a less noble metal— usually zinc or aluminium. While the metal corrodes, the electrons supplied to the object allow the reduction of the tarnish layer. Although simple, this method presents some drawbacks, like the progressive contamination of the solution by the corrosion products of the active metal and also limitations with respect to the choice of applicable solution. 

Ethanol is widely acknowledged to be less aggressive toward metals and elastomers than methanol, but little research and development has been devoted to the specific problems posed by ethanol. Ethanol typically has more water in it than methanol (an artifact of production) which may affect solubility of contaminants and corrosion potential. One ethanol contaminant that can arise from production is acetic acid, which is water-soluble and will corrode some automotive fuel system components. For instance, General Motors found that E85 caused more corrosion in fuel pumps than M85, presumably because of a higher level of dissolved contaminants [3.2]. Since much more development has been devoted to compatibility with methanol fuels, the general approach for ethanol has been to use materials developed for methanol, even though they may be over-engineered. ... 

The atomic radii of Cu, Sn(1.45 A), and Zn(1.42A) are also nearly identical, allowing for a full gamut of Cu/Sn and Cu/Zn alloy concentrations to be produced, known as bronze and brass, respectively. Although the use of bronze dates back to at least 3,000 B.C., there are also early examples of brass artifacts that date back to ca. 2,200 B.C. in India. Most likely, the discovery of bronze resulted from the inquisitive mixing of available metals at the time, only to discover that Au/Sn alloys possessed a greater strength than iron steels were not developed until thousands of years later. Since zinc metal was not available until the mid-18th century, and tin was readily obtained, the widespread production of bronzes occurred at the expense of brasses. In the absence of pure zinc, early formulations of Cu/Zn alloys were most likely... 

Some applications of NMR microimaging and EPR spectroscopy to the study of disease and senescence processes in plant organs are presented, with emphasis on the non-invasive nature of the techniques. A particular strength of the use of NMR microimaging in research on live specimens is its ability to perform repeated measurements on the same specimen. From EPR spectroscopy information specifically on free radicals and paramagnetic metal-containing species was produced. Techniques to avoid the production of artifacts from sample preparation was described in both methods. 

In Colombian green coffee, Boosfeld et al. (1994) and Boosfeld and Vitzthum (1995) elucidated the structure of two pairs of unsaturated aldehydes, (E,E)-2,4- and (2F,4Z)-2,4-nonadienal as well as (E,E)-2,4- and (2 , 4Z)-2,4-decadienal, probably generated via autoxidation of unsaturated fatty acids and contributing particularly to the typical green-coffee odor. The products were identified by mass spectrometry, GC-FTIR and NMR spectroscopy. The authors used particularly mild extraction techniques in order to avoid artifact formation and isomerization of the conjugated double bonds. The sensory impressions of these aldehydes at the sniffing port varied from metallic, fried, and flowery to oily notes. 

---