A novel combination of analytical techniques for measuring optical properties of glaze and paint as input for computer modelling is used to investigate the influence of the green glaze layer present on top of the black underpainting in the background of Girl with a Pearl Earring. The absorption spectra of paint layers from paint reconstructions and samples of the original painting were determined using micro spectrophotometry. Additionally, Bidirectional Reflectance Distribution Function (BRDF) measurements were done on paint reconstructions to determine the reflection distribution from multiple illumination and observation angles. Already existing height and layer thickness information was compiled in a digital 3D model of the painting which, in combination with the optical properties, was used as a base for rendering using the Mitsuba render engine. The experimental results clearly show that the green glaze layer under specific angles darkens the appearance of the black paint onto which it is applied. The computer simulation shows promising results for digitally recreating the painting.

Parts of the Southwest Palace of Sennacherib (700 BC), which were located in Nineveh (Iraq), are now destroyed by the ongoing conflict in Iraq and Syria. The palace rooms used to be decorated with numerous Assyrian reliefs. Luckily, digital pictures of the site are available thanks to an Italian expedition in 2002. The goal of this research is to physically reproduce the destroyed reliefs using this photo database. First photogrammetry was used to rebuild the global dimensions of the reliefs. The details are reconstructed by fusing a highly detailed depth map retrieved with Shape from Luminance (SFL), together with a coarser Artificial Reconstruction. The fused reconstruction was evaluated with the eigenvalues of the Hessian. The eigenvalues give an intuitive measure about the shapes of the reliefs. The RMSE of the results improve up to 44.4% compared to the usage of an intensity (grey) image. The final 3D models are used to produce full size reproductions with 3D printing and CNC milling.

Rembrandt was a unique painter of his era, and one of his most outstanding pieces is The Jewish Bride. He mastered the art of manipulating pigments to create unique paint mixtures and textures. This can be seen in his painting, The Jewish Bride. In the background of The Jewish Bride, Rembrandt mixed five pigments together: bone black, red earth, smalt (a blue pigment), yellow earth and yellow lake. Smalt and yellow lake are unstable pigments in oil and their colour fades over time. Due to the degradation process of smalt, the oil matrix and the top layer have both changed its appearance into a transparent monochrome brown. The colour loss and change of colour affect the pictorial impression created by the painting. The goal of this thesis is to digital colour reconstruct the background of The Jewish Bride to show how it might have looked when non-degraded smalt and yellow lake were present. In this work, the painting is analysed with different micro and macro techniques: microscopy, SEM-EDX, Macro-XRF, and hyperspectral imaging. The outcomes of microscopy, SEM-EDX and Macro-XRF are combined to show the distribution and to quantify the amount of smalt and yellow lake in the background. Knowing the distribution of smalt and yellow lake in the painting made it possible to digital mix the colours back to their primary appearance. To achieve this, the hyperspectral data were used, together with the Kubelka-Munk theory. This was later transferred to RGB values, which results in a digital colour reconstruction. The digital colour reconstructions show a trend of what the painting might have looked like, at the time Rembrandt painted it.

The appearance of a painting cannot solely be described by the depiction that it presents to the viewer. When viewing the artifact in real life, we find that the painted surface is in effect a three-dimensional landscape of paint. Paintings, “moveable, largely two-dimensional images created for the primary purpose of providing a visual experience”,1 can be created using a vast variety of materials on a range of supports. They are commonly built up as a complex stratigraphy of layers, generally consisting of a support, ground layer(s), one or multiple layers of (semi-) transparent paints, and in many cases a protective varnish layer. The current appearance of a painting is determined by the way a painter used and applied the materials, but also effects of aging, conservation and restoration treatments, which all continue to influence the physical state of a painting. Historically, cultural heritage (CH) reproductions were hand-crafted, and created for instance to disseminate or replace artworks, or to train in the skill of their creation. Also modern reproductions — or facsimiles — are still large hand-crafted, and for instance serve to provide access to (fragile) artworks or even complete (CH) sites, or to recreate their original appearance. Alternatively, reconstructions might reside only in the virtual domain. The continued development of digital imaging and digital fabrication technology (i.e. 3D printing) provides new opportunities for appearance reproduction, also suitable for application in the CH domain. If we want to replicate material appearance, we need to understand how (the appearance of) material is perceived. A material is, however, not observed directly, but has to be lighted, and via the light that is scattered by the material humans can perceive it. Appearance is therefore the light-material-confounded proximal stimulus for the human visual system (HVS). Even though we see, recognize and interact with a vast number of materials every day, and can effortlessly distinguish between them, it turns out that the perceptual mechanisms that underlie this, are still quite poorly understood, including linking individual appearance attributes to measurable and fabrication parameters. One of the consequences of this is that an integrated approach to (total) appearance reproduction, including color, topography/ texture/shape, gloss and transparency/translucency, is still lacking. @en

This thesis explores convincing stuff depicted in 17th century paintings, with the primary aim of understanding their visual perception. ”Stuff” is the term first introduced by Edward Adelson in 2001 to differentiate materials from objects, and to call attention on the research gap in material perception. In an interesting parallel, the representation of materials in paintings constitutes a knowledge gap in art history as well. Both gaps have only recently been recognized and started to be addressed in their respective research fields. In this thesis, representation and perception come together to create a virtuous circle in which the knowledge of painters about the representation of materials is used to understand the mechanisms of the visual system for material perception, and this is in turn used to explain the pictorial features that make the representation of materials so convincing. The common thread used here to connect representation and perception, is ”The big world painted small”, a long-forgotten booklet of pictorial recipes written by the Dutch painter Willem Beurs in 1692. We argue that this book represents an index of key features for material perception, that means an index of image features that always work as perceptual cues regardless of the illumination and the viewing conditions of the depicted scene. The main research objective of this dissertation is: To understand the convincing depiction and perception of materials in 17th century paintings, connecting the image features found in paintings and listed by Beurs to their role as perceptual cues. In order to achieve this objective, we employed a novel, interdisciplinary research approach, merging science of human and computer vision, technical art history, and the historical textual source of Beurs. @en

The different phases in the life of archaeological objects can be described by artefact biography. This dissertation defines an updated version: artefact biography 2.0, and the life phases of Early Iron Age bronze studs from Oss-Zevenbergen, the Netherlands, are elaborated. Throughout the thesis, the research revolves around information value. The bronzes have been studied from an interdisciplinary point of view, which has allowed the extraction of information that is also applicable to other corroded bronzes in general. It is argued that: - corrosion products and inclusions may reflect original microstructure
 - corrosion inhibitor BTAH binds to Sn and SnO2 - technical investigations before conservation increase the information value of an artefact.@en

This dissertation presents a study into the ultraviolet irradiation-initiated degradation phenomena occurring in titanium white containing oil paints, commonly referred to as photocatalytic degradation. The topic of this thesis can be summarized as: the (photocatalytic) properties of titanium white pigments in oil paints and their consequences for collections containing modern art. The thesis consists of three parts: 1) characterization of the use and properties of titanium white pigments, 2) understanding and monitoring the degradation of titanium white containing oil paints and 3) predicting degradation caused by titanium white pigments. Combining the results of these three parts leads to a risk management strategy for modern art collections presented as a conclusion of this thesis. Titanium white pigments were introduced in the 20th century as an alternative for lead white and zinc white. The pigments underwent a gradual development resulting in a large variety of pigments available throughout history. This variety ranges from very photocatalytic or ‘bad’ pigments, which severely speed up degradation, to photostable or ‘good’ pigments which can protect their environment from UV irradiation. Both ‘good’ and ‘bad’ pigments found their way into artist materials and thus into paintings. Hence the question ‘Titanium white, Friend or Foe?’. The pigment’s photocatalytic activity is highly dependent on the pigment’s crystal structure (rutile or anatase) and (inorganic) surface treatment. When a pigment is photocatalytic, radicals can form upon UV irradiation, which attack the oil binding medium and break it down to volatile components, leading to an effect called chalking: the pigment is unbound on the paint surface. Interestingly, while we know that ‘bad’ TiO2 pigments were used in modern oil paints, photocatalytic degradation problems have not been widely reported thus far. Several hypotheses for the lack of problems in collections are presented and investigated in this thesis. Additionally, characterization tools, predictive tools, and monitoring tools are developed, in order to provide solutions before it is too late. Simultaneously, analytical methods and research approaches, that are uncommon in the field of conservation science are explored to evaluate their applicability in answering cultural heritage research questions. @en