Wilda Christine B, Burnstock Aviva, Suhling Klaus, Mattioli Della Rocca Francesco, Henderson Robert K, Nedbal Jakub
Department of Physics, King's College London, Strand, London, WC2R 2LS United Kingdom.
The Courtauld, Somerset House, Strand, London, WC1X 0RN United Kingdom.
Herit Sci. 2023;11(1):127. doi: 10.1186/s40494-023-00957-w. Epub 2023 Jun 16.
The removal of varnish from the surface is a key step in painting conservation. Varnish removal is traditionally monitored by examining the painting surface under ultraviolet illumination. We show here that by imaging the fluorescence lifetime instead, much better contrast, sensitivity, and specificity can be achieved. For this purpose, we developed a lightweight (4.8 kg) portable instrument for macroscopic fluorescence lifetime imaging (FLIM). It is based on a time-correlated single-photon avalanche diode (SPAD) camera to acquire the FLIM images and a pulsed 440 nm diode laser to excite the varnish fluorescence. A historical model painting was examined to demonstrate the capabilities of the system. We found that the FLIM images provided information on the distribution of the varnish on the painting surface with greater sensitivity, specificity, and contrast compared to the traditional ultraviolet illumination photography. The distribution of the varnish and other painting materials was assessed using FLIM during and after varnish removal with different solvent application methods. Monitoring of the varnish removal process between successive solvent applications by a swab revealed an evolving image contrast as a function of the cleaning progress. FLIM of dammar and mastic resin varnishes identified characteristic changes to their fluorescence lifetimes depending on their ageing conditions. Thus, FLIM has a potential to become a powerful and versatile tool to visualise varnish removal from paintings.
去除表面清漆是绘画修复中的关键步骤。传统上，通过在紫外线照射下检查绘画表面来监测清漆的去除情况。我们在此表明，通过对荧光寿命进行成像，能够实现更好的对比度、灵敏度和特异性。为此，我们开发了一种轻便型（4.8千克）便携式宏观荧光寿命成像（FLIM）仪器。它基于一台与时间相关的单光子雪崩二极管（SPAD）相机来获取FLIM图像，以及一台脉冲440纳米二极管激光器来激发清漆荧光。通过对一幅历史模型画作进行检测来展示该系统的性能。我们发现，与传统的紫外线照明摄影相比，FLIM图像能以更高的灵敏度、特异性和对比度提供有关绘画表面清漆分布的信息。在使用不同溶剂涂抹方法去除清漆的过程中和之后，利用FLIM对清漆及其他绘画材料的分布进行了评估。用棉签在连续涂抹溶剂之间监测清漆去除过程，结果显示图像对比度会随着清洁进程而变化。对达玛树脂和乳香树脂清漆进行FLIM检测，发现其荧光寿命会根据老化条件发生特征性变化。因此。FLIM有潜力成为一种强大且通用的工具，用于可视化绘画上清漆的去除情况。
