Dr. Rosie A. Grayburn, associate scientist and laboratory manager, Department of Conservation at the Winterthur Museum, explained why the Raman technique is ideal for analyzing cultural heritage pieces.
Dr. Grayburn writes, "The ability to examine objects in situ using the sizeable chamber of the Renishaw inViaTM confocal Raman microscope meant that answering these research questions could be done non-destructively, which is of crucial importance when studying unique objects of cultural relevance."
An inVia was used to analyze objects in Winterthur's scientific research and analysis laboratory which also includes some important historic discoveries.
The Denig Bible
Created around 1784, and handwritten and illustrated by Ludwig Denig, this Pennsylvanian German bible is a unique piece. Raman analysis facilitated a distinguishing of two different blue colorants in its pictures, Prussian blue and indigo, which are difficult to distinguish by eye alone. It was revealed by Raman analysis that Prussian blue was detected in some green colourants, which suggests that the color was achieved as a mixture of a blue and an, as-of-yet, unknown organic yellow pigment.
Image Credit: Renishaw plc – Spectroscopy
Case Study: Winterthur Museum Renishaw inVia Denig Bible
A technique that is centuries-old, indigo dip dyeing uses a resist in order to create patterns on the textiles dyed in a reduction vat. In order for oxidation to fix the dye onto the fabric, the fabrics are then removed from the vat and exposed to air. Due to the expertise required, indigo can also be directly applied manually onto textiles, although this is extremely rare. There are many conflicting statements about which is the earliest record of this between publications and curators globally.
Image Credit: Renishaw plc – Spectroscopy
Typically, it is cited that this was first achieved in England in 1738, by the use of arsenic as an indigo reduction agent. However, there are Indian printed and painted textiles from as early as the 12th century, within the Winterthur Museum's textile collection, as well as in many other global textile collections. According to conservators and curators, it appears that this blue has been applied using a brush instead of being dyed in a vat. The Raman technique was used by research fellow Alka Raman in order to investigate these blue dyes.
It was therefore essential for this purpose to establish that indigo was the blue painted on to the cloth in the collection from India. Through use of in-situ Raman sampling using the Renishaw inVia Raman spectrometer with a 785 nm diode laser, four painted Indian textiles were identified for initial examination.
The presence of indigofera tinctora was indicated in all textile samples studied by a very strong peak at 1577 cm-1, which was measured from blue areas of the textiles. Indigofera tinctora was used pre-20th century, and is the one of the main plant species from which natural indigo is derived. The presence of indigo in the areas deemed by curators to be painted was confirmed by this crucial breakthrough. It allowed further investigations into the reduction methods and chemicals used to delay the re-oxidation of indigo, to enable it to be manually painted onto the textile.
More About the Winterthur Museum
Located in Delaware, in the United States of America, the Winterthur Museum showcases decorative arts popular in US culture over the centuries and has an unparalleled collection of nearly 90,000 objects made or used in North America since 1640.
The collection is displayed in a magnificent 175 room house, much as it was when the family of founder Henry Francis du Pont called it home. The house is situated within 1,000 acres of protected meadows, woodlands, ponds, and waterways. The 60 acre garden, which was designed by du Pont, is among one of the US' finest. The museum's graduate degree programs and extensive research library make Winterthur an important center for the study of American art and culture.
For more information about Winterthur Museum, please follow this link: www.winterthur.org
This information has been sourced, reviewed and adapted from materials provided by Renishaw plc - Spectroscopy.
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