Michele R. Derrick

FOURIER TRANSFORM INFRARED SPECTRAL ANALYSIS OF NATURAL RESINS USED IN FURNITURE FINISHES

Infrared spectroscopy is a valuable method for the detection and identification of organic coating materials. The vibrational bands that appear in the infrared spectra provide information on chemical functional groups of a sample which may allow for general characterization of the material or even the identification of specific compounds. Mixtures of natural materials, as are often found in furniture finishes, can stretch conventional infrared spectroscopy to its limits as an analytical method. This paper outlines the capabilities and limitations of Fourier transform infrared spectroscopy for the identification of natural resins used in historic furniture finishes.

SULFURYL FLUORIDE (VIKANE): A REVIEW OF ITS USE AS A FUMIGANT

Sulfuryl fluoride, sold commercially as a fumigant by Dow Chemical Company under its trademark Vikane, is currently being examined for use in museums and historic structures as a pest control agent. While little to no visible damage to materials is noted when Vikane is properly used, the selection criteria for a museum fumigant must be founded on an in-depth analysis of its possible effect on the physical and chemical properties of exposed artifacts. This article forms a basis for the evaluation of sulfuryl fluoride by providing a comprehensive review on Vikane, including information regarding the uses, chemical reactivity, physical properties, efficacy, and toxicity of sulfuryl fluoride.

EMBEDDING PAINT CROSS-SECTION SAMPLES IN POLYESTER RESINS: PROBLEMS AND SOLUTIONS

AbstractPolyester resins have been commonly used in art conservation for embedding paint cross sections prior to microscopic and analytical studies. These resins set rapidly without heat, are clear, polish readily, and microtome easily. While they work well for embedding most paint samples, they pose pro blems for some specific samples. The polyester embedding media have been found to dissolve wax, some organic colorants, and fresh natural resin layers in cross sections. The embedding resin also wicks into porous samples of low binder content. At times, infiltration can be desirable for its consolidating effects, but it can also interfere with the determination of the type of binder in the sample by producing blotchy, uneven staining results and by obstructing infrared analysis. Alternate embedding materials and procedures are discussed in this paper. One method to prevent the infiltration of embedding media is presented in which the samples are precoated with a thixotropic acrylic gel before embedding. O...

Photo-induced chemiluminescence: A sensitive probe of oxidative changes in organic materials

Abstract An instrument has been developed for the measurement of weak photo-induced chemiluminescence (PICL) emissions produced from solid samples at ambient temperatures. Analysis of the kinetics of a general reaction mechanism indicates that the intensity of the emissions is directly proportional to the concentrations of available unoxidized species. Preliminary investigations of PICL show the technique is sensitive enough to measure changes in organic materials resulting from exposure to a single photographic flash or to light sources of varied spectral distribution. The initial application of chemiluminescence measurements to organic materials found in artifacts is for the detection of deterioration either at very early stages or at very small levels of change. Examples of experimental results on new, naturally aged and artificially aged materials show that the technique offers promise in many applications.

Simple encoding of infrared spectra for pattern recognition Part 2. Neural network approach using back-propagation and associative Hopfield memory

Abstract By extending an adaptive momentum back-propagation two-layer network with a final associative Hopfield memory the networks total error convergence could be improved remarkably. This design enables simultaneous calculations of the networks weights and biases ( batch calculating network). Using only energy-orientated inputs of the mid-infrared spectra of 104 multi-functional carbonyl compounds, the networks were trained by 25 structutal features 104-fold for each of three input sets (19, 27 and 38 inputs). In a comprehensive statistical investigation the behavior was studied of the networks response to the increase of artificially produced noise to the inputs. Some of the chosen structural features to train the network remain reliable by increasing the disturbance of the input data and can be related to special regions of the original infrared spectra. Therefore the resulting network design could be suitable to verify the reliability of further structural features for classes of organic compounds other than carbonyl compounds.

FURNITURE FINISH LAYER IDENTIFICATION BY INFRARED LINEAR MAPPING MICROSPECTROSCOPY

Abstract Infrared linear mapping microspectroscopy is a new teclmique that can provide information about the composition, position, and size of individual layers in a multilayered sample. Resin coating samples from multilayered facsimiles as well as cross sections of finishes taken from historical furniture were microtomed with and without the use of embedding media. A linear mapping routine was then used to systematically collect infrared spectra from each microtomed sample by sequentially moving the sample in 20 μm steps under an aperture of 20 × 400 μm. The resulting spectra were used for identification of components in individual layers on the samples. The advantages and limitations of the analysis technique are discussed using finish samples taken from 16th-, 18th-, and 19th-century furniture.

SOME NEW ANALYTICAL TECHNIQUES FOR USE IN CONSERVATION

AbstractStandard analytical equipment found in modem laboratories can answer most questions asked about samples. New equipment designs or new approaches are sometimes needed, however, to answer very specific questions that arise. Examples of four techniques with potential applications and benefits to the field of art conservation are described. (1) Infrared mapping microspectroscopy is a method used to provide a “picture” of the location of components in a small sample, such as a paint cross section, based on an array of infrared spectra. (2) Environmental scanning electron microscopy (E-SEM) has the capabilities of a SEM but is especially designed to operate at near atmospheric pressures without conductive coatings on the samples. It can also be used to image dynamic processes in real time at high resolution. (3) Organic elemental analysis (OEA or CHNS-O) provides quantitative information on the amounts of carbon (C), hydrogen (H), nitrogen (N), sulfur (S), and oxygen (O) in a combustible material that c...

THE EFFECTS OF SOLUTION APPLICATION ON SOME MECHANICAL AND PHYSICAL PROPERTIES OF THERMOPLASTIC AMORPHOUS POLYMERS USED IN CONSERVATION: Poly(vinyl acetate)s

AbstractThe tensile properties of solution-cast poly(vinyl acetate) (PVAC) films are determined by the thermodynamic quality of the solvents. Higher strength and lower elongation are evident in polymer films of poly(vinyl acetate) AYAT (Union Carbide) cast from a solution of acetone or an acetone/ ethanol/water mixture, while lower strength and greater elongation are evident in films cast from a solution of chloroform or toluene after drying for 180 days. Films of PVAC-AYAT cast from a toluene solution retained a significant amount (>4%) of solvent, while films cast from the other three solvents retained little solvent (>0.3%). For all polymer films, the glass transition temperature (Tg) was elevated greater than 18°C above the Tg of the bulk polymer. The differences in the tensile properties of the films with little retained solvent is explained on the basis of the thermodynamic quality of the solvents, 1.e., the physical properties of the solution-cast polymer film in the dry state may be affected by th...

The Use of Ft-Ir Spectrometry for The Identification and Characterization of Gesso-Glue Grounds in Wooden Polychromed Sculptures and Panel Paintings

Traditional Western techniques for gilding of polychromed sculptures and panel paintings include the use of grounds prepared by the application of a first layer of gesso grosso followed by a gesso sottile layer, as described by Cennino Cennini in his treatise on painting techniques. These techniques have been used in Italy since the Middle Ages, and were later adopted by many artists in regions of the new world under Spanish and Portuguese rule, sometimes with local variations in materials and techniques. This article discusses the use of Fourier transform infrared spectrometry (FTIR) for the identification of inorganic materials present in the grounds of Baroque wooden polychromed sculptures from Minas Gerais, Brazil. This technique allows the quantitative analysis of the separate layers of the grounds, with respect to the anhydrite/gypsum ratio present in the sample. The technique has several advantages over the one currently used (Debye-Scherrer chamber for x-ray powder diffraction). FTIR spectra can be obtained in a few minutes allowing quantitative results, while x-ray diffraction usually takes more time and does not give accurate data for quantitative studies. The article also discusses the results of the studies of the grounds in Brazilian polychromed sculptures and compares the original Italian technique with Portuguese and Spanish techniques and its variations in Brazil. -- AATA

Painted Qero Cups from the Inka and Colonial Periods in Peru: An Analytical Study of Pigments and Media

Qero cups, made from wood, ceramics and precious metals, have been used for millennia in the Andean region for ritual consumption of maize beer. From the cusp of the Inka-Colonial period, painted decoration became more common on qero cups. Most of the painted decoration actually consists of thin layers of a pigmented rubbery material that was cut and inlaid into shallow carved cavities in the wood substrate. For this project, 312 paint samples from 53 qerocups in collections of the Brooklyn Museum of Art, National Museum of the American Indian/Smithsonian Institution, Metropolitan Museum of Art, and American Museum of Natural History were analyzed. The study of paints is part of larger study of the technology of over 150 qero cups from these four collections. Samples from seven qeros in Peruvian collections have also been analyzed. Nearly two dozen pigments have been identified, including mineral, synthetic inorganic compounds, and natural dyestuffs. The binder consisted of an unusual natural resin (commonly called ‘mopa mopa’) usually mixed with a nondrying or semidrying oil. This resin, which was used at least locally during the pre-Inka period and continued to be used through the Colonial period and later, came from a tree that grows in the montana of southwest Colombia, a region that was part of the northernmost extension of the Inka empire.