‘The orange colour to be gold’


Conservation Science
May 7, 2019

The Leman Album (Museum number E.1861-1991), containing 97 early 18th-century designs on paper for woven silk fabric, is full of surprises, and keeps on giving. In addition to the discoveries made so far (some of which were described in previous posts), we have recently established that James Leman, a brilliant silk designer and master weaver, was also very fond of using a rather unusual but poisonous pigment.

Leman designs no. 81, 19, 80, 89, from left to right: many of them contain bright orange details © The Victoria and Albert Museum.
Leman designs no. 81, 19, 80, 89, from left to right: many of them contain bright orange details © The Victoria and Albert Museum.

Throughout my career as a heritage scientist, I have come across poisonous pigments almost on a daily basis: some toxic minerals also happen to have beautiful, very vibrant colours, and as such they were often chosen by artists to paint with – which means that we now find them in (or on) museum objects. For example, many of the natural minerals containing arsenic (orpiment and realgar, to name the two most famous ones) have a very vibrant hue, ranging from yellow to orange to blood red.

Specimens of mineral realgar and orpiment from the NHM collections. Photography by Mike Rumsey © The Trustees of the Natural History Museum
Specimens of mineral realgar and orpiment from the NHM collections. Photography by Mike Rumsey © The Trustees of the Natural History Museum

Centuries ago, an artist’s most obvious choice was to source these arsenic-containing minerals, grind them, and obtain the desired pigment. However, we also know that written records of recipes to make these pigments from scratch do exist as well.

Over the past 25 years, I have hardly ever come across these synthetic versions of natural arsenic pigments; little did I know that things would change once I started looking at the designs from the Leman Album…

With Rosarosa Manca, from the University of Florence, I methodically analysed a number of Leman designs, and all the orange areas turned out to contain large quantities of arsenic. We checked these areas with a powerful microscope to see what the pigment particles looked like: there were yellow, orange and red grains – so we thought we had an assortment of arsenic-containing minerals.

Leman design under the microscope: grains of arsenic pigments magnified 500 times.
Leman design under the microscope: grains of arsenic pigments magnified 500 times.

When we tested each individual particle with our Raman microscope, we found that we did not have a natural mineral after all, but an arsenic glass, which is a synthetic material. How unusual! Arsenic glass has been recently studied, and was detected on a number of objects (see the work by Vermeulen et al. and Grundmann et al., among many others).

Specimens of arsenic glass, before grinding. © Gunter Grundmann (left), © Daniel Modl (right).
Specimens of arsenic glass, before grinding. © Gunter Grundmann (left), © Daniel Modl (right).

But this was the first time that this material was proven to have been used regularly and consistently by the same artist over the span of several years. We tested works by other designers, followers or associates of Leman’s and found that they too used arsenic glass.

What did this all prove? Far from being a rare and elusive material, arsenic glass must have been popular, at least at the beginning of the 18th century and in Spitalfields, London, where most of the capital’s silk weaving was taking place at the time.

And just in case you were worried after reading all this: even if toxic materials are present in museums, they are usually locked in stable paint layers, and it is safe for both staff and visitors to enjoy the objects.


You can read other Leman blogs here.

About the author

Conservation Science
May 7, 2019

Dr Lucia Burgio is Senior Scientist (Object Analysis) at the Victoria and Albert Museum, London. She graduated in Chemistry summa cum laude from the University of Palermo, Italy and completed...

More from Lucia Burgio
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