A Sweet Result: Saving a Dieter Roth chocolate sculpture from becoming food

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Dieter Roth, P.O.T.A.A. VFB, 1969. Chocolate, birdseed, wood. Edition 3/30 (22.5 x 24.9 x 23.1 cm) Coll. Fundação de Serralves - Museu de Arte Contemporânea, Porto. Acquisition 1999. Photo: © Filipe Braga. © Fundação de Serralves, Porto.

By Vania Assis

Although created relatively recently, modern artworks and collections pose some of the most challenging preservation projects with unusual media and volatile combinations of ephemeral nature. The artist Dieter Roth created multiple sculptures using perishable—and mostly edible—materials, often produced with the ultimate aim of destruction or absorption through the environment.

Perhaps some of the most famous works by Roth are the self-portrait multiples; these are busts depicting the artist, built using a mixed paste of chocolate and bird feed seeds. These sculptures, as part of their lives as artworks, were placed outdoors, exposed to the elements, with the final intent being for them to be consumed by nature. Upon acquisition by museums and galleries, these works would have likely been in contact with insects and gone through conditions adverse to their preservation. Long-term survival was never part of the plan, so how can we extend the life of something which wasn’t designed to last?

An (Un)expected challenge

While minimal intervention is desirable when looking after collections, particularly perishable artworks, under what circumstances does a preservation treatment become justifiable? Initially, when the artwork was created, it suffered changes and transformed according to external factors. As custodians, museums often aim to preserve evidence of these transformations as an intrinsic part of the object, especially when in line with artistic intention.

However, from the moment a work of art comes into a collection, these changes, resulting from previous exposure, are still present or may even be ongoing. The decaying artwork is not only at risk, but it can also become a danger to other museum objects. As chocolate ages its compounds separate and become more unstable, with sugars and fats crystalizing and efflorescing on the surface. This same efflorescence becomes a perfect anchor point for mold spores and a great food source for insects. It was during one of their routine collection care checks last summer that the collections team at Serralves Museum spotted something unusual. Dieter Roth’s chocolate bust, part of their collection, had become inhabited by booklice. The lice could be seen moving on the sculpture’s surface. Due to cracks and voids, the insects had plenty of space for shelter, making physical removal impossible. Common in museums, pests can show up at any time, particularly where organic or natural materials are present. With a fragile structure, the chocolate bird seed paste couldn’t be cleaned, as it was too brittle and vulnerable to touch. The unwanted guests had to be removed—and fast—to save the bust and contain the spread of the infestation.

A passive solution

The fast-thinking collections team quickly isolated the sculpture from other objects, keeping the booklice away from potential new targets. After careful deliberation, they decided that a non-invasive, controlled solution, such as an anoxia bubble, was the preferred treatment method.

EXPM has been carrying out anoxia treatments for museums and archives for over 20 years. This low-risk solution consists of isolating objects in a chamber or bubble where oxygen levels are gradually reduced by nitrogen replacement killing pests by asphyxia and dehydration without the use of toxic chemicals or pollutants. The use of nitrogen gas (N2), which is commonly present in the atmosphere, ensures that insects will not survive after prolonged containment in the bubble. At the same time, as a non-reactive gas, N2 will not affect objects, their colors or dyes.

EXPM has treated a variety of collection materials, both friable and robust, spanning various centuries and from diverse cultures. However, this was the first perishable or food-based object ever treated by the team, requiring extra special care and attention.

Upon inspection, it was clear that the insects were active; the booklice were visible walking on the sculpture but would hide away shortly after the storeroom lights were switched on. Clearly shying away from light and humans, there was no way to physically remove them all, and in addition they likely also laid eggs inside the sculpture, which meant that new cycles of infestation were possible.

The chocolate itself had developed a brittle and dried surface. It was clear that the paste had grown fragile over the years as the components tend to separate and lose moisture. While structurally the bust is still solidly attached to an inner support rod, the surface has a very friable appearance, which discouraged the team from using any type of mechanical removal procedures.

Preparing the sculpture for anoxia

The EXPM team’s first priority was to locate a working area with no traffic or vibration to install the bubble—an essential requirement to ensure no one would get too close to the fragile sculpture, as it would need to remain in the same spot for at least 3 to 4 weeks to complete the treatment. This is the minimum recommended time for exterminating these pests. Eggs from booklice can take up to 21 days to hatch, meaning that, if the treatment has a shorter duration, there is a risk of eggs surviving, and a new generation of booklice may strike back.

The team produced a large, transparent pocket with enough volume to place the sculpture upright inside. It was important to select a clear material for the pocket to keep the sculpture visible at all times and allow easy monitoring.

Considering that handling should be minimal and touching the surface avoided, the greatest risk during treatment was any contact with the pocket material when inflation or deflation took place. To offer better protection, the sculpture was placed inside an acrylic cubic frame. The heavy weight and solid structure of the cube provided rigid support while allowing the sculpture to be seen.

The protective frame with a datalogger, ready to receive the sculpture

Before sealing the bubble and reducing oxygen levels, a datalogger was placed on the inside to monitor temperature and humidity throughout the full duration of treatment. The bubble was then sealed, with two valves applied on opposite sides, to introduce nitrogen and expel the existing air from inside.

The stabilized bubble, fully inflated with nitrogen

After various cycles of nitrogen introduction, oxygen levels dropped to 0.05%. Flowing nitrogen in and expelling the air out was done gradually over the course of three hours. This process was carried out as gently as possible to avoid a buildup of pressure inside the bubble or cause damage by air displacement.

The bubble then remained sealed over 21 days – the longer the better – to ensure that all pests were extinct, reducing the chance of re-infestation.

Anoxia proved a non-intrusive, minimally interventive method that solved a complex infestation issue. Despite its small scale, the sculpture’s condition and components made treatment challenging, but the results were rewarding, and so far no more booklice have been seen.

Once again the bust has survived nature, remaining intact and uneaten.

Author Bio:

Vania Assis works as a conservator for EXPM, supporting conservation projects in Europe and the Middle East. Before joining, Vania was part of the conservation team at the M+ Museum in Hong Kong. She is the former British Library’s conservator for the International Dunhuang Project and graduated with a master’s in conservation from Camberwell College of Arts.

(Read the article in the February-March 2022 "News in Conservation" Issue 88, p. 18-23)


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It was during one of their routine collection care checks last summer that the collections team at Serralves Museum spotted something unusual. Dieter Roth’s chocolate bust, part of their collection, had become inhabited by booklice. The lice could be seen moving on the sculpture’s surface. Due to cracks and voids, the insects had plenty of space for shelter, making physical removal impossible.
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