Dutch National Heritage Lab zooms in with new SEM

icon.highlightedarticle.dark R&D Last modified: 8 May 2023
Article image of: Dutch National Heritage Lab zooms in with new SEM

The Dutch National Heritage Laboratory in Amsterdam is where heritage professionals and managers can turn with questions about the material composition, origin, decay and conservation of objects. Its researchers use state-of-the-art equipment, including a new SEM, to find answers. Senior Conservation Specialist Ineke Joosten: “If you want to know about the gilding on the Golden Coach, you turn to us.”

By Alinda Wolthuis | Photos: FOODnote

A word of warning: if you’re wondering whether that etching in your attic is a Rembrandt, don’t bother approaching the Dutch National Heritage Laboratory. This department of the Cultural Heritage Agency does not serve the general public. “We provide services for professionals and curators from museums, libraries and monuments,” says Senior Conservation Specialist Ineke Joosten.

She and a staff of twenty work in a high-tech lab housed in the same building where the Rijksmuseum has its restoration studios and research labs. Another occupant is the University of Amsterdam’s degree program in Conservation and Restoration of Cultural Heritage.

“We do research on our national cultural heritage,” Joosten explains, “ranging from the visual arts and design to natural historic collections, archeological objects, monumental buildings, interiors, archives and movable heritage. We analyze the materials, the state they’re in, and the aging processes they’re undergoing. And make recommendations on how to conserve them.”

Article image of: Dutch National Heritage Lab zooms in with new SEM
“Does the dye in this dress contain toxins?”
Ineke Joosten

Passionate about materials

Typical questions a client would ask the Dutch National Heritage Laboratory are: ‘Does the dye in this dress contain toxins?’ (Answer: Yes) and: ‘What is the “snow” used in this 1914 scale model made of?’ (Answer: Metal salts from the cement used to build the scale model houses).

Ineke Joosten is a geochemist by trade. Her involvement in archeological research into the technology of early iron production in the Netherlands landed her a job at the National Heritage Lab. “To work here, you have to be tenacious, have a wide range of interests, and be passionate about materials,” says Joosten.

“You also need to be able to work well with curators and art historians. We often analyze the SEM or Py-GCMS results together. By combining our knowledge of materials with their knowledge of the context, we are able to solve complicated questions. And sometimes, we can’t, because our research doesn’t always reveal the information we’re looking for. Our work can also be very frustrating at times. Like when you can’t determine what causes that weird haze on a painting, no matter how hard you try …”

Article image of: Dutch National Heritage Lab zooms in with new SEM
“We were asked to determine the origin of the gold used to gild the Golden Coach”
Ineke Joosten
Article image of: Dutch National Heritage Lab zooms in with new SEM

7th-century touchstone

The lab recently acquired a new Scanning Electron Microscope (JSM-IT700HR SEM) and a Cryo Cross section Polisher (IB-19520CCP), both from JEOL (see text box). The SEM is a powerful, user-friendly microscope, while the CCP is ideal for making crisp, flawless cross sections of specimens. Standard prepping by grinding and polishing may not be smooth enough for the SEM.

“We’re still exploring all the options and haven’t got all the applications down pat, but we’ve already done some great analyses,” Joosten says. “Recently, we were sent an early medieval touchstone from a dig in Utrecht. Touchstones were used to determine an object’s silver or gold content. You’d take the object you wanted to check and make a mark with it on the touchstone. You’d then compare this ‘object mark’ with a mark made by a sample needle of known gold or silver content. We were asked to determine whether there was gold on this particular touchstone and, if so, what its chemical composition (or alloy) was. The curators also wanted to know whether the stone had been used to test more than one object. These are not exactly easy questions to answer about a 7th-century archeological find. A stereoscope revealed a lot of small gold particles on the stone. A SEM can be used to analyze particles at micron level. We decided to focus on any particle larger than 200 microns, because otherwise the analysis would have taken far too long. But you know what we found? Traces of at least ten different alloys!” The dig that yielded the touchstone also contained coins. The lab has been asked to analyze whether these coins were tested on the touchstone. “That would give them a wonderfully complete story for their museum.”

“Studying how materials are altered by the use of lasers: this SEM makes it possible”
Ineke Joosten
Article image of: Dutch National Heritage Lab zooms in with new SEM
Article image of: Dutch National Heritage Lab zooms in with new SEM

Royal Golden Coach

In addition to questions about an object’s origin and use, Joosten also deals with conservation issues. “There was a tiny chip in the paint of a small painting on a copper panel. So we took a tiny sample of the paint, embedded that in synthetic resin and polished that to get a clear cross section. We then used the SEM to analyze this sample and found copper chloride in the bottom layer of the paint. This might be the reason why the paint is flaking off. Things like that are useful to know when deciding how to restore and conserve a painting.”

A prestigious project is the lab’s research into the gilding on the Golden Coach used by the Dutch monarch. “Currently, the Amsterdam Museum is displaying the coach in a special exhibition. In preparation for the exhibition, the curators wanted to know as much as possible about it. They asked us to find out where the gold used to gild the coach was from. The gold leaf was really extraordinarily thin, less than one µ. We took a cross section and polished it with our cross section polisher. We could never have done this using a conventional polishing method, because gold is so soft and can easily smear. The CCP allowed us to measure the gold layer’s thickness with great accuracy and to determine whether we’re dealing with the original gilding. Our next step is to collaborate with the Vrije Universiteit’s isotope lab to determine the lead isotope ratios and the chemical composition of the gold leaf, and then to compare the results to those of Surinamese and South African gold.”

New opportunities

Investing in this equipment has created new opportunities for the lab. “We’ve only recently gotten the SEM, so we’re still learning and exploring our options. One thing we want to do in the future is take cross sections of paper samples to study the effect of conservation treatments. We would also like to study how materials are altered by the use of lasers. This SEM puts us in a position to do that.”

Technologies: SEM and CCP

To study and analyze materials at nano level, the Dutch National Heritage Laboratory uses a new, innovative JSM-IT700HR SEM. The SEM has an electron gun with a 1nm spatial resolution and a 300 nA maximum probe current. Its user-friendly software interface simplifies observation and analysis. The compact instrument also features a large specimen chamber with multiple accessory ports and EDS integration.

The IB-19520CCP Cryo Cross section Polisher is designed to minimize thermal damage by cooling the specimen with liquid nitrogen during processing. The consumption of liquid nitrogen is limited, allowing for long cooling periods. Specimens are cooled rapidly when immersed in liquid nitrogen. The polisher is designed to ensure that the whole process, from polishing to observation, is conducted without exposing the sample to the air.

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