No Salt Please

British Museum

Removing salt efflorescence from a plaster cast of the first part of a Maya Calendar

This is the top of Stela A at Quiriguá. When A.P. Maudslay worked at the site in the 1880s he had a mould made of the inscription, which was transported to London where a plaster cast was made.

This is the cast in the British Museum storage. Now a hundred and twenty years old, it requires some conservation. Casts like this one are our best record of how the original monument looked, since a further century of weathering has eroded the surface of the original monument. Conservation work on the casts is therefore vital to retain details that might otherwise be lost.

When relative humidity (R.H.) of the local environment rises above 60%, the naturally occurring salts in the chemical structure of plaster become soluble. Fluctuations in R.H. allow the salts to move towards the surface of the cast where the moisture evaporates and salt crystals form.

The formation of salt crystals softens the surface of the plaster and results in the loss of definition and detail. The surface of the cast is pitted where the salt crystals have displaced the plaster.

The cast after brushing with a soft brush; note the dust at the base of the cast.

Detail, after conservation.

After conservation. Notice the contrast appears greater than in images prior to conservation. This is due to the removal of dust, yet discolouration of the surface still exists and the white areas appear brighter.

Looking at details on the casts and updating line drawings like this one helps epigraphers today to further understand and decipher the intricacies of Maya writing.

Credits: Story

All images © Trustees of the British Museum
Text and image selection: Amy Drago
Thanks to: Claudia Zehrt, Kate Jarvis, and other BM Google Maya Project collaborators

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.