Analysis of the Lycurgus Cup - revisited. A fresh insight into its composition using current analytical Instrumentation

Session

Analysis and Imaging in Heritage Science

Authors

Mr Neil Wilkinson (2), Dr George Fern (1), Dr Ashley Howkins (1), Prof Ian Freestone (3), Dr Tobias Salge (2), Dr Brett Clark (2), Dr Alex Ball (2)

Affiliations

1. Brunel University
2. Natural History Museum
3. UCL

Keywords

Lycurgus Cup

Dichroic

Roman Glass

Nanoparticles

transmission Electron Microscopy

TEM

STEM

Scanning Transmission Electron Microscopy

Micro-CT

EDX Analysis

EDX mapping

microanalysis

3D

Au Ag

Glass technology

Abstract text

Summary

Whilst the collective wealth of data and theory regarding the Dichroic nature of the glass used in the famous 4th century Roman Lycurgus Cup is substantial, hands on practical analytical research on this very special object has not been undertaken for nearly 35 years. During that time there have been substantial developments and improvements in all Analytical Scientific instruments and many new ways for data collection have become available.

In particular, Transmission Electron Microscopes are now able to scan/raster very small electron beams to produce images and other analytical data streams at up to atomic resolution – the TEM/STEM Microscope.

Specimen preparation for TEM has also advanced such that ideally thin specimens, typically of around 100 nm thickness, can be made from precisely chosen areas in bulk samples. The FIB - Focussed Ion Beam instrument.

3D imaging using X-Ray beams can produce density images to reveal internal structural details. The Micro-CT instrument.

This work takes advantage of all of the above instrumentation to substantiate existing ideas and knowledge and more.

     

Introduction

The Lycurgus Cup is a 4th Century Roman cage cup, which exhibits extraordinary optical properties. When viewed in reflected light, it is an opaque pea green colour, but is a ruby-red colour when viewed in transmitted light. This optical property is known as Dichroism. The Lycurgus Cup is the only known complete object of this period and type which shows this optical property.  Other small fragments that have been found, but none match the stunning and vivid colours of the Lycurgus cup.

This optical property is understood to be the result of additions of Nano Particles during the manufacture of the glass. Several modern day attempts have been undertaken to replicate the glass of the cup and have shown similar results.

 In the 4th Century AD, its quite remarkable for this technology to have been developed.

 

The overall glass composition has been analysed in a number of previous studies (1,2,3), many of which noted the presence of Silver and Gold in addition to the elements typically used at the time for the making of glass objects.

 

In the 1990 publication by Barber & Freestone, (4), a Transmission Electron Microscope ( TEM ) was used for the first time to try to identify the chemistry and structure of the glass cup itself and importantly, the Nano Particles it contains, which have long been believed to be the source of the Dichroic properties of the glass. Their work. reported Nanoparticles of approx. 50 nm. These were analysed with EDX in TEM mode and confirmed to contain Au and Ag but there was also evidence of small amounts of Cu.

 

TEM’s and TEM specimen preparation in the late 1980’s were prone to producing carbon contamination on the specimen being viewed and often scattered electrons within the sample area produced X-Rays not derived from the specimen itself. These issues were noted on the 1990 Barber and Freestone paper.

Modern TEM/STEM microscopes do not suffer from the above artefacts.

  

Method

A small piece of glass from the Lycurgus cup was imaged in a Micro-CT instrument to try to determine if the glass was homogenous and possibly help choose a suitable sites for FIB TEM sample preparation.

The sample was images in a modern high resolution Stereo microscope to produce 3D optical images. These too helped to determine the homogeneity of the glass and helped in the choosing of the locations to prepare FIB samples for the TEM/STEM work.

Further work followed, using an SEM fitted with EDX to help determine the best site to FIB prepare samples for TEM/STEM analysis and to analyse the bulk composition of the glass.

Samples have been prepared using a FIB from areas chosen from the above studies.

These samples, used in a modern TEM/STEM have been used to locate the nanoparticles, measure and analyse their composition and to estimate their density within the bulk material.  

 

Results

Images and results from all of the above described techniques will be presented to show in more detail the Nanoparticles within the glass and their composition and structure.

 

Conclusions

The wealth of new information revealed by the modern instrumentation and methods used in this study can be used to derive new insights into how this 4th Century AD Roman vase may have been produced.  

 

References

1 THE ROTHSCHILD LYCURGUS CUP: AN ANALYTICAL INVESTIGATION

R. C. Chirnside and P. M. C. Proffitt,   Journal of Glass Studies   Vol. 5 (1963),  pp. 18-23 (6 pages)

2 Chirnside, R. C. and Proffitt, P. M. C., 1965, Letter to the Editor, J. Glass Studies, 7, 139-40

3 Brill. R. H., 1965, The chemistry of the Lycurgus Cup, Proceedings of the Seventh International Congress on Glass, compres rendus. 2, paper 223, 1-13, Brussels.

4 An investigation of the origin of the colour of the Lycurgus Cup by Analytical Transmission Electron Microscopy.

D.J.Barber & I.C.Freestone

Archaeometry 32, 1 (1990), 33-45. Printed in Great Britain