Institute of Physics, Nicolaus Copernicus University, ul. Grudziadzka 5, 87-100 Toruń, Poland.
Acc Chem Res. 2010 Jun 15;43(6):826-36. doi: 10.1021/ar900195d.
Identification of the order, thickness, composition, and possibly the origin of the paint layers forming the structure of a painting, that is, its stratigraphy, is important in confirming its attribution and history as well as planning conservation treatments. The most common method of examination is analysis of a sample collected from the art object, both visually with a microscope and instrumentally through a variety of sophisticated, modern analytical tools. Because of its invasiveness, however, sampling is less than ideally compatible with conservation ethics; it is severely restricted with respect to the amount of material extirpated from the artwork. Sampling is also rather limited in that it provides only very local information. There is, therefore, a great need for a noninvasive method with sufficient in-depth resolution for resolving the stratigraphy of works of art. Optical coherence tomography (OCT) is a noninvasive, noncontact method of optical sectioning of partially transparent objects, with micrometer-level axial resolution. The method utilizes near-infrared light of low intensity (a few milliwatts) to obtain cross-sectional images of various objects; it has been mostly used in medical diagnostics. Through the serial collection of many such images, volume information may be extracted. The application of OCT to the examination of art objects has been in development since 2003. In this Account, we present a short introduction to the technique, briefly discuss the apparatus we use, and provide a paradigm for reading OCT tomograms. Unlike the majority of papers published previously, this Account focuses on one, very specific, use of OCT. We then consider two examples of successful, practical application of the technique. At the request of a conservation studio, the characteristics of inscriptions on two oil paintings, originating from the 18th and 19th centuries, were analyzed. In the first case, it was possible to resolve some questions concerning the history of the work. From an analysis of the positions of the paint layers involved in three inscriptions in relation to other strata of the painting, the order of events in its history was resolved. It was evident that the original text had been overpainted and that the other inscriptions were added later, thus providing convincing evidence as to the painting's true date of creation. In the second example, a painting was analyzed with the aim of confirming the possibility of forgery of the artist's signature, and evidence strongly supporting this supposition is presented. These two specific examples of successful use of the technique on paintings further demonstrate how OCT may be readily adaptable to other similar tasks, such as in the fields of forensic or materials science. In a synergistic approach, in which information is obtained with a variety of noninvasive techniques, OCT is demonstrably effective and offers great potential for further development.
鉴定画作结构各层的绘制顺序、厚度、组成，以及可能的来源，即其层理，对于确认画作的归属和历史以及规划保护处理非常重要。最常见的检查方法是分析从艺术对象上采集的样本，包括通过显微镜进行的视觉分析和通过各种复杂的现代分析工具进行的仪器分析。然而，由于其具有侵入性，取样与保护伦理不太兼容；从艺术品中取出的材料数量受到严重限制。取样也有很大的局限性，因为它只能提供非常局部的信息。因此，非常需要一种具有足够深度分辨率的非侵入性方法来解析艺术品的层理。光学相干断层扫描（OCT）是一种对部分透明物体进行非侵入式、非接触式光学切片的方法，具有亚微米级的轴向分辨率。该方法利用低强度的近红外光（几毫瓦）获取各种物体的横截面图像；它主要用于医学诊断。通过连续采集许多这样的图像，可以提取体积信息。自 2003 年以来，OCT 已被应用于艺术品的检测。在本报告中，我们简要介绍了该技术，讨论了我们使用的仪器，并提供了读取 OCT 断层图像的范例。与之前发表的大多数论文不同，本报告重点介绍了 OCT 的一种非常具体的用途。然后，我们考虑了该技术成功实际应用的两个例子。应一个保护工作室的要求，对两幅来自 18 世纪和 19 世纪的油画上的铭文的特征进行了分析。在第一种情况下，有可能解决一些与作品历史有关的问题。通过分析与画作其他层相关的三个铭文涉及的油漆层的位置，解决了其历史上的事件顺序。显然，原始文本已被重绘，其他铭文是后来添加的，因此提供了关于画作真正创作日期的令人信服的证据。在第二个例子中，对一幅画进行了分析，目的是确认艺术家签名伪造的可能性，并提出了强有力的证据支持这一假设。这两个在绘画上成功使用该技术的具体例子进一步表明，OCT 可以很容易地应用于其他类似的任务，例如在法医学或材料科学领域。在协同方法中，通过各种非侵入性技术获取信息，OCT 被证明是有效的，并具有很大的发展潜力。
