Dusan Stulik

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...

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.

Long-Term Protection of the Last Judgment Mosaic in Prague

A sol-gel coating was used in the long-term protection of the 14th Century mosaic situated above the gates of St. Vitus cathedral, in the center of Prague Castle. The choice of a sol-gel coating is the result of a research effort involving both on-site testing in Prague and accelerated ageing of various polymers and sol-gel materials in the laboratory. The coating selected for treatment of the entire 13 m × 10 m mosaic is a multi-layer system in which an organic-inorganic sol-gel layer is placed between the glass substrate and a fluoropolymer coating. This coating combination performed very well in an accelerated weathering chamber as well as during onsite testing. Since the top layer is scheduled to be removed and re-applied periodically, it is hoped that this concept will allow long term protection to the largest outdoors mosaic north of the Alps. On-site application of the coatings on the entire mosaic started in 1998 and will be completed in 2000.

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...

Applications of environmental scanning electron microscopy in art conservation and archaeology

The principles of environmental scanning electron microscopy (E-SEM) are explained and discussed. The performance of the E-SEM compares favorably with the performance of traditional SEM instruments. This new technology has significant advantages in art conservation and archaeology. The authors describe several pilot studies which explored potential uses of the E-SEM. Electron micrographs recorded from moist, outgassing, and difficult to coat samples are presented, together with x-ray spectra recorded from uncoated samples of electrically nonconductive materials.

Dynamic Studies of Materials Using the Environmental Scanning Electron Microscope

Dynamic studies allow the observation of microscopical changes of materials over time as various factors alter an object. Using this methodology, processes important in art conservation and archaeology such as the wetting and drying of consolidated and unconsolidated building materials or the corrosion of metals from air pollutants can be studied in situ and in tempora. The development of the Environmental Scanning Electron Microscope has made it possible to videotape these dynamic processes at nearly the same resolution limits as traditional SEM technologies without elaborate sample preparation. Experiments examining salt crystallization, shrinkage in adobe, and lead corrosion illustrate the value and applicability of the new E-SEM technology.