Explainer: Analytical chemistry a secret weapon in conserving museum objects

In Conservation, located in the cool white underbelly of Melbourne Museum, objects conservator Charlotte Walker is preparing a psychedelic Jenny Bannister jacket ready to go on display in the Melbourne Story gallery.

The sleeveless tunic – made by the nationally significant designer when she was only 14 and attending Red Cliffs High School in Victoria – is laid out face down on a white bench. 

The influence of David Bowie’s Ziggy Stardust is evident in the design, which is accented by loud hand-cut red, green and pink stars appliqued onto a black, purple and red background. 

The garment has already spent two weeks in the freezer – at minus 20 degrees – to kill off any pests, things like carpet beetles or webbing clothes moths. 

Next, Walker will rely on the museum’s secret weapon – analytical chemist and materials scientist, Dr Rosemary Goodall – to find out more about the jacket’s material composition. 

Both Walker and Goodall are based at the Museums Victoria Research Institute, where Goodall’s scientific techniques help to conserve items in the vast museum’s archive. 

Today, most museums and galleries employ scientists in similar roles, and there are even specialist courses in conservation science. It’s a testament to the usefulness of science in informing the management of museum collections.  

Goodall’s analysis informs everything from preservation and storage, to repairs and exhibition, as well as safe handling protocols.

“Because you start with a very large natural sciences collection, that was in some cases 150 years old. And they really liked to put arsenic and mercury on those objects 150 years ago. We’re dealing with that legacy. And so it’s really important in handling all those things correctly,” Goodall stresses.

Her work relies on three main pieces of high tech kit and analytical techniques.

The first, a handheld X-ray Fluorescence Spectrometer, looks like a bit radar gun. “It’s point and shoot,” Goodall says. 

“They really liked to put arsenic and mercury on those objects 150 years ago. We’re dealing with that legacy”

Dr Rosemary Goodall

The instrument identifies what elements are present, information vital for identifying hazards and heavy metals, things like lead paint or mercury.

“You shoot a beam of x-rays at the material. It excites the atoms and electrons inside […] and when electrons drop to fill the vacancies, they emit a fluorescence which is what we measure,” she explains. Those emissions are unique for each element, enabling Goodall to determine which ones are present.

The next tool in this analytical chemist’s toolkit is a Fourier transform infrared spectrometer (FTIR). This device is small and movable, avoiding the need to cart large and heavy museum objects from their storage.

The FTIR spectrometer uses infrared radiation to shed light on an object’s chemical composition, this time molecules rather than just elements. 

Goodall says, a beam of infrared radiation from the FTIR spectrometer excites molecules within an object, say a textile, and the radiation causes those molecules to vibrate in different motions like rocking or bending.

The result is a unique fingerprint with bands at known wavelengths, which Goodall compares against her “enormous library of 20,000 spectra”.

“I can do a spectra of a textile, go search the library, and come back and say, ‘well, that looks like an acetate fabric’, or ‘that looks like a nylon fabric’,” she says. 

For Walker, whose job it is to preserve, conserve and exhibit the vast array of objects in the museum’s collection – everything from motorcars to teacups to historical dresses – the information provides crucial insights.

“As conservators we study how materials are made, how they degrade and how to try to prevent them from degrading,” she says.

Knowing what something is made from is a “great help” in determining the conditions for storage and display, elements like lighting, humidity, temperature, and security, she says. 

“For example, if something is identified as wool, we know that it’s going to be really susceptible to pest attack, that it’s going to be potentially susceptible to changes in humidity, potentially susceptible to light. So, we can put in place strategies to prevent those degradation processes from happening, or to try and slow down those degradation processes,” Walker says.

Another example, when silk is ‘weighted’ – a process of adding salts to make the fabric heavier – the material is more likely to degrade.

The material composition can also add to an item’s back story. Metals and synthetics can be dated based on knowledge about when certain manufacturing processes were developed. 

Walker says, before the arrival of Goodall and her analytical tools, there were other methods for identification – looking at materials under a microscope, or doing tests with chemicals.

But the new technology provides the information more quickly and doesn’t harm the objects.

“As conservators we study how materials are made, how they degrade and how to try to prevent them from degrading,”

Charlotte Walker

The museum is currently working with the University of Melbourne on research analysing different plastics within its collection – what types there are, how and when different plastics begin to break down.

“Some of the old projectors and tape recorders, you can get up to ten different plastics on those objects. There’s the plastic casing, the buttons, the spools, they can all be different plastics,” Goodall says.

Some plastics are highly unstable, crumbling and breaking down rapidly. Putting them on display can accelerate that process. It’s a challenge for museum conservators whose goal is to preserve the collection on behalf of the people of Victoria as well as share it with the public through exhibitions. 

That’s critical for textiles, particularly the archive from Jenny Bannister who loves using plastic in her creations. 

“We’ve got one of her dresses that I analysed 24 different plastic objects – that wasn’t all of them – and I probably identified about six or seven plastics,” Goodall says.

Sometimes this poses a dilemma for conservators.

After discovering a cardigan with cellulose nitrate buttons, a material which can damage wool as it degrades, conservators added tiny shields behind each button to better preserve the garment.

Another, trickier example is a turban hat with fake pearl beads. Those are also cellulose nitrate and degrading, a process triggering copper metal fibres in the hat to turn green. Yet here, unlike the cardigan, it is difficult to separate the materials without impacting on the item’s integrity.

Walker says, in those cases, the materials analysis feeds into a discussion involving multiple people – curators, conservators, collection managers and Goodall. 

“It’s not a decision that would be made by one person [… ] we discuss these things together and work out what will be the best option for that object. And that might also consider whether or not it’s suitable for display in the future. Or whether we decide that we’re going to digitise it and put it on the website and accept that it might not be displayed in the future because it is in such poor condition.” 

Goodall’s third technique is called micro-fading.

“It’s meant to be a very quick way of telling whether something will fade when it goes under lights on display,” she says.

Here she shines a tiny – 300 microns – but intense beam of light onto a fabric and measures any change in colour over ten minutes. The results are compared against the ‘blue wool standard’, an internationally used measure of fabric fading (on a scale of 1 – 8) used by the fashion industry and in the development of washing powders. 

“Blue wool one fades very rapidly. It goes up to eight which barely fades at all. If something fades similarly or worse than level one, we would not put it on display for very long, we may not put it on display at all,” Goodall says.

When Bannister’s colourful jacket goes on display, it will be illuminated by gallery lighting specially designed for displaying textiles. 

After testing all the different materials and colours, micro-fading revealed special care was needed with the green fabric, mostly used on the shoulders. This was most susceptible to fading under light, Walker says. 

It illustrates how materials science is informing the work of conservators in better understanding, preserving and preparing museum objects for exhibition.

“The existing showcase lighting is in the top. So, we’re going to be in discussions with the technical operations team to see if we can light it from underneath instead, which will just allow us to keep this wonderful coat on display a little bit longer.”