A Portable Dynamic Laser Speckle System for Sensing Long-Term Changes Caused by Treatments in Painting Conservation.

Alberto Pérez,Rolando González-Peña,Eva Pérez–Marín,Fernando García-Diego,Ángel Perles,Roberto Braga Jr

doi:10.3390/s18010190

Abstract

Dynamic laser speckle (DLS) is used as a reliable sensor of activity for all types of materials. Traditional applications are based on high-rate captures (usually greater than 10 frames-per-second, fps). Even for drying processes in conservation treatments, where there is a high level of activity in the first moments after the application and slower activity after some minutes or hours, the process is based on the acquisition of images at a time rate that is the same in moments of high and low activity. In this work, we present an alternative approach to track the drying process of protective layers and other painting conservation processes that take a long time to reduce their levels of activity. We illuminate, using three different wavelength lasers, a temporary protector (cyclododecane) and a varnish, and monitor them using a low fps rate during long-term drying. The results are compared to the traditional method. This work also presents a monitoring method that uses portable equipment. The results present the feasibility of using the portable device and show the improved sensitivity of the dynamic laser speckle when sensing the long-term process for drying cyclododecane and varnish in conservation.

Highlights

Digital holography [1,2], a well-known speckle interferometric technique, is generally used to measure paints as they dry, the technique demands complex experimental configurations that limit its use [3,4]
Portable equipment for monitoring the activity of painting treatments during the restoration of paint in situ presented reliable outcomes that were comparable with the equipment used in an optical laboratory
In other areas of knowledge, the portable equipment can be used to monitor activity in the analysis of seeds, sperm motility, fruit maturation, as well as in food evaluation tasks completed outside optical laboratories

Summary

Introduction

Digital holography [1,2], a well-known speckle interferometric technique, is generally used to measure paints as they dry, the technique demands complex experimental configurations that limit its use [3,4]. Other digital speckle pattern interferometry techniques, such as shearography, are applied for art objects, canvas and panel paintings [5,6], but require a similar experimental holographical configuration. Treatments usually change the visual aspect of the art objects. The processes that provide fixation and consolidation in painting conservation use numerous substances, among which is cyclododecane (which forms bright artefacts on the surface, changing the final aspect of the object) [10,11,12]. One way to control the impact of art restoration is by managing the Sensors 2018, 18, 190; doi:10.3390/s18010190 www.mdpi.com/journal/sensors

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Conclusion