The Behavior of Different Varnishes Applied to Graphic Artworks: Comparison Using a Methodological Protocol

ABSTRACT

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.

KEYWORDS:

• Conservation
• paper
• varnish
• artificial aging

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The current study was carried out under the auspices of the Spanish Ministerio de Economía y Competitividad within the framework of the ‘R&D MAT 2014-58659-P’ research project.