Analysis brings answers for the Spangled Bed!

Emma and I recently took samples of metal thread and spangles from the Spangled Bed for the purpose of analysis.  Using resources provided by the Institute of Archaeology at University College London. They were to be analysed with optical microscopy and scanning electron microscopy.

Emma and Lesley carefully remove some thread and spangle samples from the Spangled Bed.

Emma and Leslie carefully remove some thread and spangle samples from the Spangled Bed.

 Close up of appliqué embroidery on the Spangled bed.

Close up of appliqué embroidery on the Spangled bed.

SEM: Scanning Electron Microscopy is a process by which the elemental composition of materials can be determined by exposing samples of material to an electron beam which reflects off the sample surface at an angle. The angle of reflection is measured by the machine, which uses standard angle measurements of different elements to determine the elements that compose the sample being tested.

Scanning Electron Microscopy

Scanning Electron Microscopy machine.

By using this method it has been possible to determine, once and for all, the composition of the spangles which has long been an unanswered question. We took the opportunity while we had access to the machinery to analysis some of the metal threads from several other important pieces, such as the King’s Bed and one of X-frame chairs of state.

Additionally, photographs using a digital microscope were taken of the threads and spangle samples under high magnification. These show the construction of the threads and the corrosion products which have formed over time.  Images of the spangles can be seen in the photographs below, before and after an experimental cleaning trial.
1

Spangles under magnification before cleaning. Here, it is possible to see the corrosion on a gold (left) and silver (right) spangle. On the gold spangle, it is possible to see where the threads that attached it to the textile protected the metal beneath from corrosion.

Spangles under magnification before cleaning. Here, it is possible to see the corrosion on a gold (top) and silver (above) spangle. On the gold spangle, it is possible to see where the threads that attached it to the textile protected the metal beneath from corrosion.

Gold spangled after cleaning with acetone.

The silver spangled after cleaning with acetone.

The silver spangled after cleaning with acetone.

The spangles were then mounted for analysis in the SEM.

Hitachi Scanning Electron Microscope with chamber open.

Hitachi Scanning Electron Microscope with chamber open.

Analysis results:

The green box indicates the area scanned.

The resulting spectrum shows that the most significant elements present are gold and silver.

Some metal threads were also taken from the head cloth of the bed for analysis.

Photograph of a metal thread under ~235x magnification.

Photograph of a metal thread under ~235x magnification.

Photograph under ~30x magnification.

Photograph under ~30x magnification.

The green box indicates the area scanned.

An electron image of the same sample of thread.

The sampled thread proved to include gold, silver, copper, and traces of several other elements which make up the corrosion products.

Manufacture and Deterioration of the metal threads:

Metal thread is made by hammering gilt silver very thin and cutting it into fine strips which are wrapped around a textile core. Silver and other metals present in such threads are susceptible to the agents of deterioration.

The chief component of the black tarnish that forms on household silver is silver sulphide, which starts in damp conditions (the rate of the tarnishing reaction accelerates about 70% relative humidity). It is caused by the reaction of silver with sulphur in the air. In the past, there were many sources of sulphur in historic houses, such as tobacco smoke and degrading wool fabrics. Many other gaseous pollutants also affect metal threads.

Conservation:

As metal thread is composed of two very different materials, with different strengths and properties, the cleaning of metal threads is one of the most difficult challenges in textile conservation. Methods which clean the textile elements (water, detergents, and solvents) are too gentle to clean the metal threads and methods for removing tarnish and corrosion products from the metal elements (stronger solvents, abrasive pastes, and acids) are too strong for use on the textiles. Silver sulphide is insoluble in solvents and must be removed with acids.

The results of the analysis have answered some long standing questions and will inform the National Trust textile conservators on exactly what materials they are dealing with for cleaning trials on parts of the bed fabric later this year.

Leslie
Conservation Intern
MSc Conservation for Archaeology and Museums, UCL

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