Calibrated UV Reflectance Photography for Lepidoptera Collections
In this research, calibrated digital ultraviolet (UV) reflectance microphotography, using a UV-converted Nikon D200 with a Baader Ultraviolet Venus lens filter, was used to record UV reflective and UV absorbent markings on the wings of male butterfly specimens, Hebomoia glaucippe sulphurea. Handmade reflectance standards were prepared using magnesium oxide, plaster and carbon, and photographed with the butterfly. UV reflectance photography was compared with visible light photography, transmitted and reflected visible light microscopy, and scanning electron microscopy to characterise the deterioration of UV reflective and UV absorbent butterfly wing markings. The handmade reflectance standards were effective in calibrating the digital photographs, allowing for each pixel of the digital photograph to be used for optical densitometry. The UV reflective markings showed little evidence of deterioration, while there was clear deterioration that occurred in the UV absorbent markings. The degradation, collections care and conservation practices for Lepidoptera specimens were also investigated.
Gatorfoam Backings as an Alternative to Lining Paintings
Support for aged and deteriorating paintings has historically been provided by lining the painting with various adhesives and canvas; however, the introduced stresses and the reversibility of such a treatment is now better understood and approached with greater caution. Alternatively, a painting can be loose-lined with a solid support, such as Gatorfoam, without the use of adhesive. Gatorfoam is an inert polystyrene laminate board used in the field of conservation. Applied as a backing between the stretcher and the canvas, such a preparation would provide a stable support on which the painting can rest, reduce vibrations due to handling, and reduce the effects of varying humidity and temperature. Stiff lining supports have been shown to improve the ability of a painting to withstand deterioration factors and a backing would reduce exposure of the canvas, the most responsive element of a painting. Furthermore, the treatment is easily reversed with minimal stress on the painting. The application of Gatorfoam between the stretcher and the canvas is an invasive treatment, but justifiable in some circumstances. The qualities of the Gatorfoam backing treatment were compared with the routine practice of attaching a Coroplast sheet backing to the reverse of the painting structure, which offers similar benefits of reduced vibration during transport and decrease in the effects of fluctuating relative humidity and temperature. Sample paintings were prepared with a brittle surface coating in which natural cracking patterns developed. Coroplast backing boards were applied to one group of three canvases, Gatorfoam backing boards were applied to a second group of three canvases and the third group of three canvases remained untreated as a control. All sets of the canvases were cycled through extremes of relative humidity and were documented before, during and after the period of cycling. The success of a Gatorfoam backing to improve the longevity of a fragile painting was evaluated, although Reflectance Transform Imaging photography and subsequent image processing were not able to resolve the crack patterns in a way which facilitated comparison.
Metamerism in Complimentary Colour Mixtures of Cadmium Red and Pigment Red 254
In modern times, cadmium compounds were significant for producing a bright red pigment for artists. Cadmium red is standard for conservators’ inpainting pallets. In contemporary practice, to avoid toxic heavy metal ions, many synthetic organic compounds have been proposed to replace cadmium red. One particular pigment, PR 254, has lightfastness and colour properties that closely match cadmium red; therefore, it is being considered as a replacement for cadmium red in fine arts and conservation. This project further explores the differences in colours produced when these two pigments are used in complimentary colour mixing in acrylic paint with other typical paint mixing pigments. For this study, the six mixing pigments used were phthalo blue, phthalo green, cerulean blue, cobalt green, burnt sienna and bone black. A set of neutral tones were mixed with these pigments from the cadmium red. Attempts were made to reproduce these exact tones by eye, using PR 254 and other pigments. The L*a*b* values and spectral reflectance curves of the neutrals were measured and compared. The ΔE values and the presence of metamerisms were noted. A comparison of the corrected tints to two cadmium red hue products was made. Understanding the differences in mixing properties between historic and contemporary red pigments will help conservators, contemporary artists and technical art historians to better understand the scientific difference between the colours mixed from these two pigments.
Chitosan as a Consolidant for Fragile Silk
Silk textiles in museum collections are often degraded and fragile, but no satisfactory treatment currently exists to strengthen or consolidate deteriorated silk. Recently, chitosan has been investigated as a consolidant for artifacts, including silk textiles. Chitosan is the N-deacetylated derivative of chitin, a linear polysaccharide found in the exoskeleton of crustaceans and other natural sources. Chemically, chitosan is (1→4)-2-amino-2-deoxy-β-D-glucopyranose, which has a chemical structure similar to cellulose, but with an amino or acetyl functional group substituting the hydroxyl group at carbon #2. Among its many properties, chitosan is non-toxic, anti-microbial, soluble in dilute acids, non-soluble in organic solvents, and capable of hydrogen and electrostatic bonding with organic substrates. Importantly, chitosan is capable of coating and strengthening textile fibres. Chitosan was applied to silk fabrics to test its effectiveness and suitability as a consolidant for textile conservation. Chitosan was dissolved in dilute acetic acid in distilled water to give 0.5% or 1% w/v solutions. The sample substrates were a new, white silk habutai fabric, and two naturally aged and degraded silk damask fabrics. Silk samples were treated by immersion in 1% or 0.5% chitosan solutions for 15 minutes followed by rinsing in distilled water for five minutes, or simply by immersion in 0.5% w/v chitosan without subsequent rinsing. Some samples were artificially aged by 100 hours of thermal aging at 50oC and 65% RH, and light aging under a bank of fluorescent lights. Tests were conducted to assess the strengthening effect of chitosan, and to see if treatment caused stiffening or colour change in the silk substrates. Samples were imaged by optical microscopy and scanning electron microscopy; tested for tensile strength, stiffness, pH, and colour change; spot-tested with solvents; and analyzed by Fourier transform infra-red spectroscopy and x-ray fluorescence.
Treatment and Prevention of Tears in Historical Rawhide Drumheads Using BEVA 371 Film Using Traditional Lining Materials
The conservation of drumheads present a unique challenge when compared to other skin artifacts as drumheads are under constant tension. This is because of the wooden hoops on which the rawhide is stretched, which also changes dimensionally when exposed to a fluctuating environment. The objective of the experiments was to assess the potential longevity and re-treatability of conserving rawhide drumheads with BEVA 371 film. The project determined the most appropriate backing material by testing Reemay, Hollytex and Japanese paper, which are traditionally used materials on deer rawhide. Tensile strength tests were performed according to the American Standards for Testing Materials D2209-00. The samples were then backed with the different lining materials using heat to activate the adhesive. The samples were subjected thermal aging at 80% relative humidity (RH) and 60°C in order to stress the skin and simulate the fatigue of the material that comes with age. Samples were run against a set of aged samples of rawhide without any lining treatment. All lining materials were also manually tested for ease of removal. Reemay was found to be the best choice for lining material as it both impedes tears from forming, and existing tears from spreading after being lined as well as being easily removed.
Light Bleaching of Paper without Aqueous Immersion: Assessing the Possible Damage
Introduced into paper conservation practice in the 1970s, aqueous light bleaching is considered a safe and effective method of reducing discolouration on paper objects. The treatment necessitates immersing the object in a bath of water and exposing it to intense light for several hours. Clearly, it is only possible so to treat objects that can undergo prolonged immersion in water. The aim of this study was to investigate the feasibility of non-aqueous or non-immersion light bleaching of paper. Specifically, it was desired to establish whether significant damage was inflicted on the cellulose component of paper during these treatments. The scope of the study was restricted to the effects of the treatments on cellulose and cellulose deterioration products; effects on other substances that may be found in papers were not considered. Whatman no.1 filter paper, both new and that having undergone a short thermal aging period, was exposed to ultraviolet-filtered artificial light in three conditions: dry, humidified in a water vapour chamber, and immersed in a bath of deionised water. Damage to the paper resulting from the three treatments was assessed via three methods: the zero-span breaking strength test, viscometry analysis, and the cold extraction pH test. No change in the properties of cellulose as a result of light exposure was detected by these methods. A further study, using more thoroughly degraded paper, is recommended.
Micro X-ray Computed Tomography for Identification of a Pseudomorph from the Elizabeth and Mary Shipwreck
A 17th century British ship, the Elizabeth and Mary, was sent to capture Quebec during the Sir William Philips expedition. The boat sank during its return voyage in 1690 near Baie-Trinité, Quebec, after an unsuccessful journey. Along with the ship, all of the artifacts present onboard were brought to the seabed and left untouched for centuries until the 1995 excavation. Among the artifacts recovered was a strange concretion of metal. When X-ray analysis was performed, a small but unidentifiable mechanism was revealed within the concretion.
The object is very small in dimensions (2.5 x 2.4 x 1.8 cm). It can be described as a pseudomorph. Micro X-ray tomography was chosen as the main tool for studying the artifact. A total of 1014 x-ray portal images were taken with a XRadia MicroXCT-400 3D X-ray microscope. A radiographic three-dimensional (3D) volume was reconstructed and the results were studied with the Aviso7.0 computer program. Through manual segmentation, each component of the mechanism was identified and color-coded. The connections between different pieces were clarified and a simplified 3D model was built with SketchUp, a basic 3D modeling program.
The resulting images were sent to specialists in different fields for identification. Historians, anthropologists, archivists, craftsmen and engineers were consulted and multiple theories on the subject were explored. The segmentation was then taken further by searching for discrete components that were overlooked the first time. After a long period of research, the artifact was finally identified as a padlock. Its operation mode was brought to light, and a physical model of a 3:1 scale was built.
The Evaluation of Modified Laponite Solvent-Gel as a Poultice in Paper Conservation
Laponite RD is a type of synthetic silicate that forms a clear, colloidal gel when hydrated in water. The working properties of Laponite are dependent on the formulation of the gel, which can be modified with the addition of solvents and additives. The focus of this study was how the introduction of additives into a Laponite-acetone gel will affect its efficacy as a poulticing material. The thickening agents, either xanthan gum or sodium carboxymethyl cellulose (CMC), were added into the Laponite solvent-gel to minimize the lateral movement of the poultice in an effort to limit the development of tide lines. The solvent-gel was evaluated based on the degree of residual deposition and, by association, signs of discolouration that remained on the paper surface after treatment. Lens tissue, Japanese gampi silk tissue and heavy silk rayon sheet were tested to determine which material would best serve as a barrier layer in reducing Laponite residues. Paper substrates were treated with the solvent-gel and were artificially aged in order to investigate the potential long-term effects of residues on the stability of paper. The Laponite-acetone gel was applied to artificially aged samples of masking tape to illustrate the effectiveness of the poultice on modern adhesive tapes. Analytical techniques such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) were used for the identification and quantification of Laponite trace residues. Visual observations in the form of colorimetry and long ultraviolet light (UVA)-induced visible fluorescence demonstrated that Fabriano paper was less likely to retain poultice residues, and the addition of additives did not appeared to reduce the lateral movement of the poultice. The gampi silk tissue was the most effective in minimizing the deposition of residues, whereas the lens tissue performed poorly as a barrier layer.
Gellan Gum: Investigating Applications as a Solvent Gel
Gellan gum is a polysaccharide from the bacteria Sphingomonas elodea. Gellan gum has been introduced as a poulticing material in paper conservation, however little is published on the potential uses of gellan gum as a solvent gel. It is possible that gellan gum can be made into a solvent gel by introducing the solvent into the gel mixture before the gel sets or by applying the solvent onto the surface of the gel before it is applied in treatment to remove aged 3M Scotch® #810 MagicTM Tape. Ultraviolet fluorescence photography was used to document the presence of adhesive residues before and after gellan gum treatment. Scanning electron microscopy (SEM) was used to observe and analyze the possible gellan gum gel residues left behind on the adhesive and paper substrate after the gellan gum treatment. Fourier transform infrared (FTIR) spectroscopy was used to analyze the occurrence of both the adhesive and gellan gum residues. In addition, colorimetric measurements were taken before and after aging of the paper samples. It was found that solvents miscible in water could be incorporated into the gel matrix resulting in a functional solvent gel. The three solvents, methanol, ethanol, and 2-propanol, were used in the experiments. Ultraviolet fluorescence photography documented that each solvent caused the adhesive residues to move laterally through the paper substrates. Results from SEM and FTIR analyses showed that no gellan gum residues remained after treatment. In summary, a workable solvent gellan gum is possible and effective in solubilizing adhesive residues on paper.
The Impact of Microlight Microspheres on the Mechanical Properties of the Acrylic Medium High Solid Gel
The impact of microspheres on the mechanical properties of High Solid Gel (Matte) by Golden was studied in order to find a light-weight fill material for losses in high impastos on canvas. The density of a fill for oil-paintings on canvas should be close to or less than that of the original material in order to prevent the formation of stress in the canvas and surrounding original paint. This is especially important when larger amounts of fill material are needed, for example, where losses need to be filled in thick paint layers and areas of high impastos. Microspheres can fill a volume with very low weight material; however, their use in the field of paintings conservation has not been reported. The suitability of the microsphere-based bulking agent MicrolightTM # 410, made by epoxy manufacturer WestSystem, was investigated. Different proportions of this low density bulking agent were tested in combination with the acrylic dispersion High Solid Gel (Matte) by Golden Artist Colors. Qualitative analyses showed that the handling properties of the fill materials were negatively affected by the addition of Microlight. The percentage of shrinkage upon drying decreased by more than 10% after addition of Microlight, but was still higher than 35%. The density of the dry fills before ageing was decreased by 40% to 50%, depending on the quantity of Microlight added. The other samples were aged thermally and by exposure to ultraviolet light. Strength and flexibility of the infills were measured by uniaxial tensile tests and by bending over Mandrels of different diameters before and after ageing. The modulus of elasticity increased after addition of Microlight, and it increased even more after ageing. Colour measurements showed noticeable colour changes for all materials tested. Comparing test results to those of the acrylic fill material Becker’s Latex Spackle, one of the materials used for filling losses in thick paint layers, showed, that the impact of Microlight on the mechanical properties of High Solid Gel was not important enough to make it suitable for filling losses in layers of oil paint.