March 2023 ESRFnews

16

CULTURAL HERITAGE

S T E F C A N D É

known paintings, The Night Watch. Finished in 1642,

this huge oil painting of a company of guardsmen setting

off in ragtag formation was pivotal in the Dutch Golden

Age for its extreme use of light and shadow, and the

depiction of subjects not in static pose but in almost

chaotic motion. However, it is in far from a perfect state:

years gone by have seen the canvas be brutally cropped,

poorly refurbished and even vandalised – twice with

knives, and once with sulphuric acid.

X-ray powder diffraction (XRPD) is able to precisely

highlight inorganic compounds. Using a prototype,

portable XRPD system developed back in 2011 by

scientists at the University of Antwerp in Belgium

in collaboration with the ESRF, Victor Gonzalez

(now at the Université Paris-Saclay) and others in the

Rijksmuseum research team recently studied the canvas

on site, behind a glass screen (image, previous page) so

that visitors could still see the painting. They wanted to

obtain distribution maps of crystalline compounds at

the macroscopic scale. To their surprise, they discovered

lead formate (PbHCOO)

2

, a compound never before

reported in historical oil paintings.

The question was how the compound got there – 

and that meant finding out precisely how its crystals

organised themselves within Rembrandt’s paint lay-

ers. Thanks to a new mode of user access to the ESRF

for cultural-heritage studies (see “The ease of bagging

beamtime”, below), Gonzalez and colleagues could

extract microscopic fragments of paint from the sur-

face of the painting, and then send them swiftly to the

ESRF’s ID13 beamline for analysis via micro-X-ray

diffraction (µXRD). (The PETRA-III synchrotron in

Germany provided complementary data.) Meanwhile,

having studied historic manuscripts of the period that

provided recipes for improving the drying time of oil

paints, Cotte experimented with dissolving litharge,

a natural mineral form of lead oxide, into linseed oil.

She was assisted by Ida Fazlić (left), a PhD student work-

ing at the ESRF under the EU’s InnovaXN programme

to integrate the needs of large-scale research infrastruc-

tures and industry – in this case the paint manufacturer

Akzo Nobel.

The synchrotron results were persuasive. When Cotte

and colleagues only partially dissolved litharge in the oil –

as a master immersed in his creative work might carelessly

do – it formed onion-like layers of lead formate around

nuclei of lead oxide just like in the real samples This

THE EASE OF BAGGING BEAMTIME

Historically users wanting to study artworks at the ESRF

usually had to submit a standalone proposal for the use

of one or more beamlines during a single sixthmonth

scheduling period This worked well when the science of

cultural heritage was being pioneered but the EBS upgrade

has brought a massive speed boost and the prospect of

studies becoming much more routine To reduce paperwork

and make access simpler and more inclusive the ESRF has

therefore introduced a new shared access mode for historical

materials The beamtime allocation group or BAG consists

of many principal investigators in the field of cultural heritage

applying jointly for beamtime on the understanding that they

distribute the access among themselves In the first test runs

in 2021 data were collected from 139 samples in the time it

would have taken previously to perform just two experiments

See esrffrBAGHG172