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This paper presents the results of a series of tests – using a recently-published set of methodological guidelines referred to here as the Protocol – on varnishes traditionally used in the protection and enhancement of graphic artworks. The aim of the research was to study the characteristics of different varnishes when they are applied to a graphic artwork and to analyze their behavior when exposed to conditions that cause alterations, be these natural factors, accidental, or the result of a conservation intervention. Lastly, the study sought to determine whether each varnish was suitable for conservation purposes. Five varnishes were selected for the study: egg white, gum arabic, shellac, rosin, and dammar. Paper test samples were used to study the characteristics of the recently applied varnishes: dimensions, weight, thickness, color, brightness/gloss, pH, surface appearance, drying time, degree of absorption by the substrate, and adhesion to the substrate. The behavior of varnishes was studied via a series of tests that recreated adverse conditions (humidity, light, and temperature). These tested for resistance to ambient humidity, immersion in water, dry-heat aging, and aging in a climate test chamber. After applying the Protocol it was concluded that the varnishes most resistant to different alteration factors are gum arabic and dammar resin. By contrast, shellac and rosin are the most susceptible to alterations, which precludes their use as a conservation material. As well as indicating the varnishes that present the minimum interaction with the substrate and the greatest long-term durability, the results of this research also provide a useful guide to the behavior of these varnishes for their use in preventive conservation. [ABSTRACT FROM AUTHOR]

This paper presents a method and protocol for the study of varnishes and be protective layers applied throughout history to graphic works. The study is based on the characteristics and behaviour of varnishes when facing different types of deterioration. The methodology is founded on a series of physical–chemical tests that identify the characteristics of a varnish when applied to paper (surface and total drying time, degree of adherence, and penetration into the substrate) and in treatments, determining its resistance to adverse conditions of humidity, temperature, and light (resistance to humidity, immersion in water, and ageing by dry heat or in a climatic chamber). The effects of these tests are evaluated by taking into account a series of physical–chemical parameters characteristic of varnishes on graphic works: weight, dimensions, thickness, texture, optical features, and pH. Variations among these parameters serve to measure the resistance of varnishes to adverse conditions and natural ageing, whether they are applied as a conservation treatment or historically. All the information necessary to facilitate the transfer of this method to researchers and professionals is compiled in a protocol. This document comprises general information, descriptions of procedures and materials, and a series of annexes that serve simultaneously to collect and to study the data. The protocol is therefore designed to serve both as a tool when applying the method and as the germ of a database for the study of varnishes on graphic works. Shellac varnish was selected to test the method and the protocol. This resin has been used in the past to provide a waterproof varnish for paper-based maps as well as for images. Errors identified during the development of the protocol were ultimately corrected by incorporating new tests, items, and annexes. The protocol has proven to be a practical tool for the study of varnishes regarding their behaviour in the case of graphic works. [ABSTRACT FROM AUTHOR]

Understanding the use of colorant materials throughout history is now the objective of multiple studies centered on the identification and characterization of these materials. The main objective of this study is to increase knowledge of the degradation pathways of indigo blue dye (Indigofera tinctoria) and the detection of degradation products. This will enable the identification of the dye on historical objects, even when it is present in a degraded state. To this end, different analytical techniques were used for the identification of indigo blue and its degradation products. Capillary electrophoresis with diode array detection (CE-DAD) and fluorescence spectroscopy were used for characterization and detection of the colorant and its degradation products caused by the aging process. Nuclear magnetic resonance (NMR) spectroscopy was used to confirm the presence of degradation products. The evaluation of color variations (lightness, chroma, and tone) in indigo blue on paper samples was made with colorimetric study, while the changes in indigo solutions were evaluated with UV-visible spectrophotometry. Additionally, changes in the alkalinity and acidity of the colorant were made with pH measurements. Lastly, the main agents responsible for the modifications that resulted in the production of degradation products of indigo blue were also identified. These methods were applied to historic samples from the Collection of Drawings, Maps, and Plans (sixteenth to nineteenth centuries) and to the thread used in the binding of a notarial record book (Registro Notarial de Torres) (fifteenth century) held by the Royal Chancery Archive in Granada (Spain). This paper provides deeper insights into the materials used in artworks and helps in the identification of indigo blue despite the degradation caused by external agents or by its natural aging process. [ABSTRACT FROM AUTHOR]