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5 - Chemical Alteration and Colour Changes in the Amsterdam Sunflowers
- Edited by Muriel Geldof, Maarten van Bommel, Marije Vellekoop, Ella Hendriks
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- Book:
- Van Gogh's Sunflowers Illuminated
- Published by:
- Amsterdam University Press
- Published online:
- 25 November 2020
- Print publication:
- 21 June 2019, pp 125-158
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Summary
Introduction
This chapter provides a description of colour changes in the Amsterdam Sunflowers due to chemical alteration of pigments, with a focus on geranium lakes and chrome yellows.
The brilliant and forceful colours of these and other late nineteenth-century synthetic materials offered artists such as Vincent van Gogh new means of artistic expression that exploited a range of contrasting hues and tints. However, geranium lakes have a strong tendency to fade and chrome yellows to darken under the influence of light. Van Gogh, like other artists of his day, was aware of this drawback, yet he continued to favour the use of both pigments up until his death in July 1890 due to the unparalleled effects they gave. In April 1888, Vincent wrote to his brother Theo:
You were right to tell Tasset that the geranium lake should be included after all, he sent it, I’ve just checked – all the colours that Impressionism has made fashionable are unstable, all the more reason boldly to use them too raw, time will only soften them too much. So the whole order I made up, in other words the 3 chromes (the orange, the yellow, the lemon), the Prussian blue, the emerald, the madder lakes, the Veronese green, the orange lead, all of that is hardly found in the Dutch palette, Maris, Mauve and Israëls. But it's found in that of Delacroix, who had a passion for the two colours most disapproved of, and for the best of reasons, lemon and Prussian blue. All the same, I think he did superb things with them, blues and lemon yellows.
Van Gogh's use of unstable colours opens a series of questions regarding the extent to which colour change affects the way his paintings look today, as discussed here in relation to the Amsterdam Sunflowers. Furthermore, given the frequency with which geranium lakes and chrome yellows occur in Van Gogh's paintings of the period 1888–90 and the predominance of chrome yellows in Sunflowers, it becomes important to understand the factors that can drive these processes of deterioration in order to develop appropriate strategies for conserving the artist's works.
4 - Methods and Materials of the Amsterdam Sunflowers
- Edited by Muriel Geldof, Maarten van Bommel, Marije Vellekoop, Ella Hendriks
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- Book:
- Van Gogh's Sunflowers Illuminated
- Published by:
- Amsterdam University Press
- Published online:
- 25 November 2020
- Print publication:
- 21 June 2019, pp 85-124
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- Chapter
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Summary
Introduction
This chapter explains the materials and techniques employed in the Amsterdam Sunflowers, enabling a comparison with the London version described in chapter 3. Building upon the 2016 article published in the National Gallery Technical Bulletin, it incorporates the latest findings gained by computer-assisted methods used to characterize the canvas support, as well as in-situ campaigns of non-invasive investigation together with further analysis of microscopic paint samples. The chapter sequence follows the steps in Van Gogh's working practice. Starting with the canvas, automated analysis of the weave enables the provenance of the canvas to be traced back to a particular roll of linen ordered by Van Gogh. Combining technical evidence with knowledge of historical manufacturing techniques further allows us to reconstruct the way in which Van Gogh divided his canvas roll into pieces used for Sunflowers and other paintings. We go on to consider how, with the original painting at hand, he used charcoal to transfer the motif of the London Sunflowers onto his blank canvas. Despite careful planning of the composition, an adjustment was required late in the working process, when Van Gogh added a painted wooden strip to extend the background above the flower at the top edge of the canvas. The artist's process of working up the composition in paint is described, paying special attention to his use of colour. The pigments and pigment mixtures used in the Amsterdam Sunflowers have been comprehensively mapped and are compared with the London picture, with discussion of some similarities and differences that account for the distinctive colour scheme of each painting. This understanding of colour application in the Amsterdam Sunflowers lays the foundation for subsequent chapters that will go on to consider the impact of light-induced colour changes that have taken place over time, and the related need to define appropriate lighting guidelines for the future safe preservation of this painting and others made with similar materials (chapters 5 and 7).
Canvas
Studying the physical characteristics of canvas picture supports is an established means of acquiring valuable information about a painter's working methods. The canvas itself is hidden by paint on the front and a second canvas is often applied to its reverse for added support.
3 - Energy scavenging and storage for RFID systems
- Edited by Luca Roselli, Università degli Studi di Perugia, Italy
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- Book:
- Green RFID Systems
- Published online:
- 05 October 2014
- Print publication:
- 25 September 2014, pp 38-75
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Summary
Introduction
Electronics is progressively penetrating more deeply into human lives: integration has made possible the wealth of many small mobile devices that society currently enjoys (e.g. smart phones, MP3 players, GPS navigation assistants, etc.). In this scenario, active RFID systems hold the promise of implementing smart environment and objects, and can ease processes in many applications fields, e.g. industrial processes, personal healthcare, environmental monitoring. Pervasive computing and wireless sensor networks are introducing their potential while power consumption has been greatly reduced thanks to energy-aware design techniques. The availability of low cost batteries has been one of the main drivers of these advances, even though it now represents one of the main limitations. In fact, power supplies still mainly rely on electrochemical cells with limited stored charge and are often impracticable to replace.
During the last years energy harvesting from ambient sources has proven to be a viable solution: the environment is an intrinsic source of low-density highly available energy [1] in either steady or intermittent and irregular forms such as, for example, vibrations [2], thermal gradients [3], indoor light [4], and electromagnetic radiation [5]. At the current state of the art, most energy harvesters can provide in practical cases an output power density of about 10–100 µW/cm3 [6]. In this scenario, mechanical vibrations represent a viable solution for powering low power electronic systems (e.g. wireless sensor nodes, personal healthcare devices, etc.).
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