This paper discusses the kinetics of aging and its implications for the evaluation of changes in the aging process, especially as applied to accelerated aging. The problem of comparing accelerated aging conditions is shown to be separate from that of evaluating changes occurring under one specific set of conditions. Thus tests and measurements that can be used to evaluate the results of a specific accelerated aging experiment are not necessarily valid for use in determining whether two sets of aging conditions are comparable. This distinction is crucial in trying to determine whether a set of aging conditions is comparable to, or accurately simulates, natural aging. The criteria for comparing two sets of aging conditions are defined, and applied to the problem of evaluating accelerated aging conditions. Data from the analysis of individual reaction products of artificially aged paper samples are used to determine the effects of temperature and relative humidity (RH) on the rates of individual reactions. Changes in the distribution of reaction products are used as indicators of changes in the aging process. The aging process of cellulose under the conditions studied (60–90°C, 30–80% RH) is shown to be RH dependent, but relatively temperature independent. Thus raising the temperature at constant RH speeds up the aging process without significantly altering it. If the RH is changed, then the aging process is altered and equivalent states of aging cannot be reached. Accelerated aging should be conducted at the same relative humidity as the conditions to which the results are to be applied. The data also indicate that lowering the relative humidity from 50% to 30% slows the rate of hydrolysis by a factor of three to five times.

Governments typically provide the water and sanitation sector with substantial amounts of public money. Monopoly power, public funds, and discretionary decisions, coupled with poor accountability, breed corruption. The best hope for reducing corruption in the water and sanitation sector is to incentivize water sector officials and managers to be responsive to citizens' demands.

Much of the information we have about history, science, culture, and civilization for the last 500 years is stored in paper-based formats. Unfortunately, changes in the technology of papermaking in the 19th century rendered the survival of much of the recorded information of a hundred year period problematic. As its use spread in Europe from the late 1400s, paper was traditionally prepared from rag fibers of cotton or linen. Such paper was quite stable, and many books and documents not subjected to physical or environmental abuse have survived in quite good condition. The demand for paper eventually exceeded the supply of rags, and the use of other sources of cellulosic fibers such as straw and grasses was explored. It was not until the late 19th century, however, with the development of mechanical equipment and chemical processes capable of converting wood to pulp that the most abundant source of cellulose could be exploited. Decades later, the relative impermanence of paper produced by

The stiffening and embrittlement of oil paints over time has been a real concern for those responsible for the long term care and preservation of paintings. This paper examines the effects of time, pigments, relative humidity (RH), temperature and solvents on the mechanical properties of traditional oil paints. In this way it is possible to determine the role of each factor in causing the paints to become brittle. Even after 14 years the oil paints show little evidence that the long term "maturing" processes have begun to slow down. It is shown that there seems to be little correlation between the time paint requires to "dry-to-the-touch" and the longer term mechanical properties. Both low and high temperature levels can increase the stiffness of the paints though the mechanisms are quite different. Considerable hydrolysis of the paints occurs early in their history and the ones that hydrolyze most quickly are the ones that remain the most flexible.

As linseed oil ages, hydrolysis and oxidation produce acid groups on the polymer chain that may lead to ionomeric behavior. The effect of these changes is difficult to determine in old paints because of the lack of records of environmental and treatment histories that can alter the physical properties significantly. A series of paints were made that have chemical properties similar to those of aged paints and that mimic old paints. Their properties seem to show flexibility as well as coherency but low strength and a high susceptibility to solvents.

There are various techniques for the restoration of artwork — how effective and safe these are also varies. ‘Reversible’ gels could, however, provide a less risky way to reverse the ravages of time.

endees at a symposium on the examination and care of ancient objects find that the materials can be as complex as the modern techniques used to examine them.

Drying oils used to formulate oil paints consist primarily of polyunsaturated triglycerides, along with smaller amounts of mono- and diglycerides, free fatty acids, and other compounds such as sterols. The drying of oils occurs through an oxidative crosslinking process that also produces smaller scission products such as short chain fatty acids and diacids. Compounds that are not attached to the crosslinked oil matrix include glycerin, the unreactive free saturated fatty acids and their glycerides, soaps of fatty acids produced by reaction with metal ions from the pigment, and scission products. As the oil ages, additional soluble material is produced by hydrolysis of glyceride esters. These relatively low molecular weight compounds can be extracted by exposure to solvents, as occurs during the cleaning of paintings. Excessive extraction of material can embrittle the paint film and affect the appearance of the paint. This paper examines the types and amounts of compounds extracted from oil paint films as a function of solvent, exposure time, pigment, and age of the paint. The results indicate that solvents vary more in the speed that they extract material than in their selectivity. The composition of the extracts is consistent with predictions based on the mechanisms of the drying and aging processes. These results confirm the importance of using the least polar solvent possible to clean paintings and to formulate varnishes.

AbstractProcesses that occur in oil paints after the initial drying stage include the hydrolysis of glyceride ester linkages, the formation of soaps, and the volatilization of low molecular weight compounds. The nature, amounts and distribution of the soluble components of paint films serve as indicators of the relative rates and extent of these processes. Comparisons of naturally aged paint with paint aged at an elevated temperature (80°C) indicate that thermal aging distorts the relative rates of these processes and does not accurately simulate the natural aging of oil paint. The relevance to conservation research of thermally aged paint, especially samples aged above the melting point of paint components, is questionable.

Chemical, physical, and mechanical properties of paper affect decisions regarding its care and treatment. Changes over time in properties including stiffness, strength, and elasticity are examined using both naturally and artificially aged samples. These properties are determined as a function of environmental conditions for new and aged samples. The rate and nature of chemical degradation processes as a function of environment are correlated with changes in physical properties. The results of appropriate accelerated aging conditions correlate with those of natural aging. The results can be used to determine physically safe ranges for the storage of paper artifacts, and to indicate how conditions within this range affect the rate of changes over time.

The chemical characterization of organic residues found in association With ceramic vessels can provide direct information on original vessel use and on diet and cooking practices of people in the past. Major improvements in analytical instrumentation have enabled the study of ever smaller samples of complex organic materials on a molecular level. Various analytical techniques have been applied to study the chemical Composition of organic residues. Volatile, non-chemically bound classes of compounds such as lipids and terpenoids have been selectively extracted and analysed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Other studies have been directed at the characterization of the condensed matrix of solid organic residues (for example, carbonized or cross-linked compounds). Non-destructive Techniques such as nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR) have been used to characterize materials based on the absence or presence of functional groups. More destructive techniques have been employed to fragment the condensed macromolecular matrix by partial hydrolysis or analytical pyrolysis. A review is presented of the possibilities and limitations of various analytical techniques. The application of organic residue analysis in ceramic studies raises many questions concerning conservation treatment of ceramics during and after excavation, as well as the long-term storage of ceramic vessels. Ceramics that may contain original organic residues should be treated as organic/inorganic composites rather than as exclusively inorganic materials. In this paper an organic residue preservation protocol is presented for conservators in the field, and sampling strategies are discussed.