In situ preservation

The skills of the conservator and the high standards of diagnostic analysis and documentation required are an essential part of any programme to investigate and preserve evidence of our past. Whenever possible the monument or building should be preserved in situ in the context and the landscape where it was created. Interest in stately homes and public buildings exceeds interest shown... 

Environmental monitoring alone does not tell anything about the actual state of preservation of artefacts preserved in situ, and should only represent one... 

In situ preservation is a form of preventive conservation, but absolute preservation in situ is not achievable. All sites are dynamic and deterioration of archaeological materials will continue, albeit at slow, and often imperceptible rates. However, environmental conditions favourable to the preservation of archaeological sites, and artefacts, can be assured by a three pronged sequence of environmental monitoring, study of the deterioration of analogous modern materials placed on a site, and the state of preservation of artefacts themselves. 

Finally, analysis of artefacts themselves should be carried out in order to assess their state of preservation. By understanding this and determining the likely pathways of deterioration the stability of a site can be assessed. Passive or active mitigation strategies can then be implemented (with further monitoring) to ensure that sites, or artefacts, preserved in situ are protected for the future. 

Fig. 19.25 A well preserved layer of white tiir-fall volcanic ash occurs in the central Wright Valley between the Heut and Goodspeed alpine glaciers. The deposit was preserved in-situ and is covered by a thin layer of lag gravel which Heill et al. (1993) identified as Ross-Sea drift. The K-Ar date (3.9 0.3 Ma) of volcanic glass in the Hart Ash is tui important reference point in the glacial history of the Wright Valley (Reproduced by permission from Hg. 11 of Hall et al. 1993)...

Preparation conditions. In order to preserve in situ biological activity of the active species, methods are required to avoid organic solvents that lower the enzyme activity. In addition, conditions should mimic the natural environment that is specific for each biomolecule, such as pH, ionic strength, temperature, or light [8,33,48,61,131],... 

In-situ timber treatment using timber preservatives... 

However, there is evidence that reactions of aluminium hydride produced in situ involve single-electron-transfer (SET) processesThe reactions described by Trost and Ghadiri have most likely not been studied in sufficient detail to permit an adequate description of the reaction mechanism to be given at this stage. It is, however, quite likely that the Grignard reactions catalyzed by copper(II) and nickel(II) complexes , as developed by julia - and by Masaki , do involve SET processes, although, if this is so, the preservation of stereochemistry in some of the examples described by these workers is quite remarkable. (In this context, the reader s attention is drawn to Reference 196, end of this section.)... 

Nixon, T. (ed.) (2004), Preserving archaeological remains in situ, Proceed. 2nd Conference, 12-14 September 2001, English Heritage, London. 

Antibody-based detection methods include immuno-cytochemistry, which gives qualitative data but has very good spatial resolution. Radioimmunoassays provide a quantitative measure of release or content. One of the major limitations of all antibody-based methods is the potential for cross-reactivity among the many peptides. For example, some of the most sensitive gastrin antisera also detect CCK, since the peptides share a common COOH-terminal tetrapeptide sequence. Methods for detection of the mRNAs encoding neuropeptides include Northern blots, which provide quantitative data and information on splice variants, but lack fine anatomical resolution. The more commonly used polymerase chain reaction, which can be quantitative but often is used in a more qualitative manner, provides great sensitivity. Alternatively, in situ hybridization preserves anatomical relationships and can be used to obtain both qualitative and quantitative data. 

In situ characterization. Catalysts should preferably be investigated under the conditions under which they are active in the reaction. Various reasons exist why this may not be possible, however. For example, lattice vibrations often impede the use of EXAFS, XRD and Mossbauer spectroscopy at reaction temperatures the mean free path of electrons and ions dictates that XPS, SIMS and LEIS are carried out in vacuum, etc. Nevertheless, one should strive to choose the conditions as close as possible to those of the catalytic reaction. This means that the catalyst is kept under reaction gases or inert atmosphere at low temperature to be studied by EXAFS and Mossbauer spectroscopy or that it is transferred to the vacuum spectrometers under conditions preserving the chemical state of the surface. 

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