David Erhardt's research while affiliated with Smithsonian Institution and other places

Publications (26)

Article
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 tha...
Article
Full-text available
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...
Article
Oil paints dry by polymerization. This 'drying' process may be substantially complete and the surface of the paint film dry to the touch within weeks, but measurable changes continue for years. Other, slower processes also continue, primarily hydrolysis of glyceride esters. This produces carboxylic acid groups as either free fatty acids (in the cas...
Article
Full-text available
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 determi...
Article
Concentrations of soluble sugars including glucose and xylose in papers produced over a range of 500 years were determined. Extraction of samples from the unprinted areas of the paper was followed by concentration, derivatisation, and analysis of the extracts by gas chromatography. The identification of the sugars was made by comparison of retentio...
Article
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.
Article
Full-text available
In the fall of 2001, anthrax-contaminated letters were sent to public figures in the United States. Chemical and radiation treatments were employed to decontaminate exposed buildings, objects, and materials. These treatments are effective, but potentially damaging to exposed objects and materials. The recommended surface chemical treatments include...
Article
One aspect of the response to a biological attack using anthrax spores sent through the mail has been to use electron irradiation to treat the mail. This irradiation procedure has altered the materials and objects in ways that were probably not anticipated. The mail was damaged by both thermal and radiation processes. Business, government, and pers...
Article
Attendees 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.
Article
Full-text available
Natural history museum collections are incomparable storehouses of geological, biological, and genetic resources throughout the world. Some of the materials composing the specimens in these collections are vulnerable to deterioration when stored in fluids. Samples were taken from liquid storage media surrounding mammal specimens in the National Mus...
Article
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...
Chapter
An understanding of the chemical and physical changes that occur in cellulosic materials is crucial to the preservation of many objects in museums and archives. Decisions regarding care, treatment, and appropriate storage environments are based on their effects on the permanence and condition of the objects. Because many of the changes that occur i...
Article
The chemical and physical state of naturally aged samples of oil paint were examined. Results were compared to those for samples of oil paint subjected to various conditions of accelerated aging. As a result, it was possible to account for the thermal aging at different relative humidities.
Article
Processes 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....
Article
The determination of an optimal value of relative humidity for the preservation of museum objects is more complex than for other environmental factors. Relative humidity affects the preservation of objects in many ways, and effects vary for different types of object. Relative humidity affects the rates of chemical reactions, and the values of physi...
Article
Full-text available
Introduction Damage to museum objects caused by acid-induced salts is a widespread problem that has been recognized for quite some time. However, the identification of the salts, required to determine appropriate conservation procedures, remains a problem. The result is that the major cause, the emission of organic acids in the environment, is not...
Article
Full-text available
A cool display case was made for a vellum document, George Washington's commission. A close fitting airtight container was used. This maintained a nearly constant relative humidity on cooling, but care was needed to minimise temperature gradients. Thermoelectric coolers were used. The showcase performed satisfactorily for one year with no change in...

Citations

... Not only can the object's responses vary wildly, but so can the sets of conditions required to evoke these responses. Within museums, this is exemplified by the contrasting RH requirements for different material and collection types (Erhardt and Mecklenburg 1994). Additionally, some objects may be susceptible to conditions that rarely or never occur in a given environment. ...
... For example, the use of long immersion times for leaching studies may yield highly accurate data on extractables, but the results may be less easily translated into conservation strategies because of the short contact times encountered in cleaning practice. Finding the optimal balance between theoretical and practical relevance of cleaning experiments has led to many discussions [24][25][26][27]. We will attempt to highlight the practical relevance of the literature discussed throughout this review. ...
... The acidic hydrolysis of b-glycosidic bonds of cellulose, often associated to oxidation, can induce reduction in the polymerization degree of cellulose and consequently structural weakening of paper (Erhardt and Mecklenburg 1995;Erhardt et al. 1999Erhardt et al. , 2000Margutti et al. 2001;Whitmore 2011). To overcome acidity and prevent such degradation processes, different deacidification treatments were studied based on the use of aqueous and non-aqueous systems (Baty et al. 2010;Hubbe et al. 2017). ...
... Long-existing awareness of the correlation between climate stability and the preservation condition of wooden heritage objects was a motivation for adopting general environmental specifications for museums as decorated wood is the key representative of objects composed of humidity-sensitive materials most vulnerable to RH and temperature fluctuations. Grounds for evidence-based environmental specifications were laid in 1990s when the key mechanical parameters-stiffness, moisture expansion coefficient, strength, strain at break and yield point were quantified for a broad range of materials relevant for cultural heritage (Mecklenburg and Tumosa 1991;Mecklenburg et al. 1998;Mecklenburg 2007), However, most of the predictive models (Mecklenburg et al. 1998;Rachwał et al. 2012) assume equilibrium of object with the surrounding environment, which is valid for slow RH variations producing little gradient of moisture content in bulk wood. In consequence, most environmental specifications to ensure the preservation of valuable collections do not take into account the environmental specificity of churches and historic houses. ...
... In turn, it is convenient to study the glass transition temperature (Tg) of each material, based on the surface measurement references that some authors have collected on this type of cleaning. Failing to take this consideration into account could cause severe fractures in the material to be preserved since exceeding the Tg of a structure causes a notable loss of flexibility, reaching a completely irreversible glassy state that will compromise its future preservation [48]. The loss of flexibility increases the risk inherent in any momentary drop of temperature, added to the lack of resistance to the vibration produced during impact. ...
... In different studies, a negligible to slight decrease in EMC was observed with increased aging of wood [33,34]. In contrast, Erhard [35] observed an increased sorption behaviour of scots pine with increasing weathering. In our own experiments, an increase of the EMC was also observed, both for natural and artificial weathering. ...
... There exists common observations in oil canvas paintings, that cracks are often formed in the area, which is not buffered by the wooden stretcher [3]. Until present, it is understood that the larger temperature and RH fluctuations related to the interaction of the air and the walls behind the painting, are the main causes of the cracks in the unprotected area of the paintings [4][5][6]. The environmental changes cause various expansion or contraction of materials in paintings based on their different mechanical properties that in turn cause uneven strain developments, which may lead to crack formations. ...
... Formaldehyde was given off by cardboard in the boxes [32]. In the 1980s, sodium formate crystals were found on the inner side of cover glasses of daguerreotype [33,34]. Glass beads from the Museum of Ethnology in Berlin, stored in chipboard cupboards, were also affected by the same phenomenon [35]. ...
... Mecklenburg, Erhardt and Tumosa´s research on the ageing processes of museum objects and linseed oil paints for art, is extensive. Examples of articles that describe accelerated and natural ageing, in order to describe the chemical deterioration processes, could be found in Erhardt, Tumosa, & Mecklenburg, 2000: Mecklenburg & Tumosa, 2001: Erhardt, Tumosa & Mecklenburg, 2005. In these articles, thermal ageing is compared to natural ageing. ...