This is something that was not visible under standard conditions, and something they didn't notice on other portraits. MSI also helps scholars to be able to read previously illegible texts. The Archimedes Palimpsest (further discussed below) is a famous example of this, but many other palimpsests have been rendered legible by this process. Multiple groups, institutions and companies work to image manuscripts using MSI and other methods to digitally preserve them, make them accessible to scholars, and improve legibility. Optical Coherence Tomography can help reveal layers and 3D visualizations of text in various media, including papyrus and paper. It has been used with multispectral imaging to provide more information about text and ink on different layers of an object. This has been used in research into papyrus mummy mask cartonnage to  image small areas of cartonnage in conjunction with narrowband multispectral imaging to reveal ink layers. Reflectance Transformation Imaging uses special procedures to create a polynomial texture map of an object. These PTMs are created from a set of images using a stationary camera and a single source of light that can be held in different positions. The following is quoted from Cultural Heritage Imaging's website:  "RTI images are created from information derived from multiple digital photographs of a subject shot from a stationary camera position. In each photograph, light is projected from a different known, or knowable, direction. This process produces a series of images of the same subject with varying highlights and shadows. Lighting information from the images is mathematically synthesized to generate a mathematical model of the surface, enabling a user to re-light the RTI image interactively and examine its surface on a screen. Each RTI resembles a single, two-dimensional (2D) photographic image. Unlike a typical photograph, reflectance information is derived from the three-dimensional (3D) shape of the image subject and encoded in the image per pixel, so that the synthesized RTI image “knows” how light will reflect off the subject. When the RTI is opened in RTI viewing software, each constituent pixel is able to reflect the software's interactive “virtual” light from any position selected by the user. This changing interplay of light and shadow in the image discloses fine details of the subject's 3D surface form. RTI was invented by Tom Malzbender and Dan Gelb, research scientists at Hewlett-Packard Labs. A landmark paper describing these first tools and methods, named Polynomial Texture Mapping (PTM), was published in 2001."