ABSTRACT

The identification of organic colorants in traditional oil paintings is an important and challenging area of conservation research. Since many organic dyes and pigments are fugitive, the detection of these materials is crucial for the proper assessment of fading, conservation treatment, and the prevention of further photodamage. While numerous methods exist to characterize colorants, recent advances in surface-enhanced Raman scattering (SERS) methodologies have enabled the unambiguous identification of various organic dyestuffs in oil paintings in a minimally invasive manner. Here, we apply a collection of SERS-based protocols to identify the organic pigments used in a number of oil paintings that were made in the Southern British colonies of North America during the eighteenth century and are being prepared for exhibition at the Art Museums of Colonial Williamsburg. Questions arose during the painting examinations that would appear to involve color shifts and possible fading. The SERS results reveal the identity of several organic pigments (i.e. carmine lake, madder lake, Reseda lake, indigo, gamboge) in these eighteenth-century portraits, within the broad-scale quantity-rich areas of the composition as well as the more challenging flesh tones and small, yet important, detail regions. We discover the continued use of carmine lake in seven of the ten paintings and identify the blue and yellow organic pigments used in this group, both of which contribute to our understanding of pigment availability and artists’ choices, as well as supporting the more accurate assessment of condition and the artists’ original intent.

摘要

传统油画中有机着色剂的鉴定是保护研究中一个重要且具有挑战性的领域。由于许多有机染料和颜料是易挥发的，因此检测这些材料对于正确评估褪色、保护处理和防止进一步的光损伤至关重要。虽然存在多种方法来表征着色剂，但表面增强拉曼散射 (SERS) 方法的最新进展使得能够以微创方式明确识别油画中的各种有机染料。这里，我们应用一系列基于 SERS 的协议来识别在 18 世纪在北美英国南部殖民地制作的许多油画中使用的有机颜料，这些油画正准备在威廉斯堡殖民地艺术博物馆展出。在绘画考试期间出现了一些问题，这些问题似乎涉及颜色变化和可能的褪色。SERS 结果揭示了几种有机颜料的特性（即胭脂红湖、茜草湖、在这些 18 世纪的肖像画中， Reseda湖、靛蓝、藤黄），在构图的大范围数量丰富的区域以及更具挑战性的肉色和小而重要的细节区域内。我们发现十幅画中有七幅继续使用胭脂红，并确定了这组作品中使用的蓝色和黄色有机颜料，这两者都有助于我们了解颜料的可用性和艺术家的选择，并支持更准确的评估条件和艺术家的初衷。