Another great read in the Restauro September issue is the article on How a turban snail cup and cover travelled from Güstrow Castle to New York .
”The State Palaces, Gardens and Art Collections of Mecklenburg-Vorpommern (SSGK MV) worked together with Professor Kerstin Kracht, a vibration technology and structural dynamics engineer, to jointly develop transport packaging that maximizes vibration reduction and shock absorption in a way that is specific to the object. This minimizes the risk of new damage during transport. (..) Collaboration with a professional partner was essential. This was all the more so given that the object would be entering the US, where specific guidelines would have to be adhered to. Bringing in a carpenter to implement the design, as had been done in the previous project, was therefore not an option. To keep the costs down, an existing, proven product was sought that would allow modifications to be made to match the calculated parameter values. The TURTLE® Climate Cabinet was chosen, a product made by the Dutch company TURTLE® that has been known for 25 years for its high-quality, sustainable art transport crates. (..) The expenditure on the protective packaging and the courier escort paid off. Unlike other objects, the fragile turban snail goblet returned home to Schwerin in March this year without any additional damage.”
Source: Restauro Magazine
Read the English translation of the original article below.
The State Palaces, Gardens and Art Collections of Mecklenburg-Vorpommern (SSGK MV) worked together with Professor Kerstin Kracht, a vibration technology and structural dynamics engineer, to jointly develop transport packaging that maximizes vibration reduction and shock absorption in a way that is specific to the object. This minimizes the risk of new damage during transport.
Loaning out artworks often presents a major challenge. The desire on the part of art historians and curators to give a wide audience access to outstanding artworks and to promote exchanges with other museums requires the assistance of the restorers responsible for maintaining and caring for the collections. The task of the restorers is to assess the feasibility of the transportation and to formulate the conditions under which transportation of the object is possible.
The question of whether a fragile object in the collection of the State Palaces, Gardens and Art Collections of Mecklenburg-Vorpommern could be transported arose in July 2018 following a request by the Metropolitan Museum of Art in New York to take an object on loan for the exhibition Making Marvels. Science & Splendor at the Courts of Europe, which ran from 19 November 2019 to 3 March 2020.
The request was for a valuable turban snail goblet, probably made in about 1600 in the Nuremberg region. The cup body consists of the shell of the rare turban snail, mounted in an engraved silver clasp. A finely worked and engraved dragon’s head forms the cover that fits on the snail shell. The shell stands on feet with claws. A brass base was added in 1752 to keep the object stable.
In addition to the fragility of the snail shell, pre-existing damage that reduced the resilience of the structure as a whole was also seen as a cause for concern. There were several small cracks around the neck. Furthermore, there was a distinct crack on the outer side of the two legs. This narrow worked section in gilt silver bears the weight of the entire object on top of it and is the connecting element between the heavy brass foot and the upper part. It was therefore thought that further mechanical stresses such as shocks, jerky movements and vibrations might produce a fracture. Various possible approaches were discussed to avoid not just this worst-case scenario, but also more minor damage such as abrasions, deformations and pressure points.
Jerky movements could, for example, be caused by mistakes when handling the object directly. To prevent this, experts would have to accompany the valuable goblet on its journey to the US. A restorer at the State Palaces, Gardens and Art Collections of Mecklenburg-Vorpommern (SSGK MV) made sure that the object and the transport crate were handled correctly.
After good experiences with her in a previous project, staff at SSGK MV decided to collaborate for the further measures with Professor Kerstin Kracht, an expert in vibration engineering and structure dynamics. The aim of the collaboration was to develop transport packaging tailored to the object in question with maximum vibration reduction and shock absorption, thereby minimizing the risk of further damage during transport.
The main focus of this development project was the object itself, in particular its vibration behaviour. A simulation model was used to estimate the first three eigenfrequencies and their associated eigenforms based on the finite element method (FEM).
The model was built using a grid of finite elements to approximate the goblet’s geometry. Each finite element was assigned a certain dynamic mechanical behaviour with specific material properties, limiting conditions and storage conditions during transit. Next, a set of equations consisting of vectors and matrices was generated based on this grid, and the equations were solved by the FEM program’s internal solver. The results gave the eigenfrequency and eigenform estimates.
This procedure for calculating the eigenfrequencies and eigenforms makes clear what parameters fundamentally affect the vibration behaviour of objects and paintings. But why understanding the dynamic behaviour of the turban snail goblet so crucial for the development of the protective packaging?
As the simulations showed, the object vibrates in its own distinctive way with specific frequencies, known as eigenfrequencies. The shape or appearance of the vibration at a given eigenfrequency is its eigenform. This means that each eigenfrequency has its own eigenform.
During transport, varying forces would be exerted on the turban snail goblet. These forces create vibrations in the turban snail goblet, which take the form of elastic deformations in the object.
Unlike plastic deformations such as dents, elastic deformations disappear as soon as the excitation stops. Even so, the elastic deformations are also a burden on the object as they can result in fatigue setting in over the course of time. This could become manifest in the form of a fatigue fracture or exacerbation of existing cracks.
The vibrations in the object due to external stimuli were the result of the summation of the various weighted eigenforms. The weightings depended on the magnitudes, directions, points of action and frequencies of the external forces. The stimuli – in other words the journey – and the turban snail goblet’s eigenmodes had to be determined in order to make it possible to minimize the amplitudes of the object’s resonant vibrations inside the protective packaging.
The State Palaces, Gardens and Art Collections of Mecklenburg-Vorpommern house a priceless collection of artworks covering many periods from Antiquity to the present day. The collection includes paintings, sculptures, modern objects, furniture, coins, craftworks, and graphic art with engravings, prints, drawings and photographs. Each year, requests are received from numerous museums in Germany and abroad wanting to include works from SSGK MV’s impressive collection in their planned exhibitions. www.museum-schwerin.de
The turban snail goblet’s vibrations in response to vibration excitations during transport are determined primarily by the eigenforms with the three lowest eigenfrequencies. The FEM analysis also showed that only the upper part of the goblet exhibited movement in the first three eigenforms. The solid stand remained stationary. This meant that the greatest mechanical stresses were to be found in the legs as the connecting element. This confirmed the suspicion that the legs constituted the most vulnerable part.
After answers had been found to these questions concerning the object’s vibration behaviour, the next step was to consider the journey. The turban snail goblet had to be picked up in Güstrow Castle, which has narrow, steep stairs, stone tiles and cobblestones in the courtyard and entrance.
It was also known that the object would be taken from Güstrow Castle to Frankfurt Airport and from New York’s John F. Kennedy Airport to the MET in a truck with air suspension. The differences in the configuration of the air suspension in German trucks compared with American ones needed to be taken into account.
A point for discussion was whether, on the flight from Frankfurt to New York, the goblet would be placed on the seat next to the courier in the plane or on a pallet along with other crates in the cargo area. The decision would have a significant effect on the design of the protective packaging and also on the procedures the courier would be expected to follow. In the first option, the protective packaging would be shaped like a small suitcase. The courier would have needed training to teach them the right way to walk when carrying the suitcase in stress situations without exerting excessive loads on the goblet in the suitcase. In July 2019 – four months before the planned transportation – it was decided that the goblet would travel on a pallet in the plane’s cargo area. In addition to the take-off and landing, this meant the package would also be carried by a forklift truck and on a conveyer belt. It was also known that the journey to New York and the journey back would be the same.
On top of the vibration minimization and shock absorption measures, the temperature and relative humidity in the immediate vicinity of the turban snail goblet would also have to be kept constant throughout the journey. The brass and the delicate parts of the goblet in particular are very sensitive to climate changes.
The many external influences to which the fragile turban snail goblet would be exposed during its journey meant that there was only one possible solution: the goblet would need to travel in its own customized microenvironment in terms of both vibrations and the climate. This could only be achieved if the object was transported in a crate that had a controlled climate in accordance with the latest construction technology standards and that could move freely in its own space with true vibration decoupling. This basic idea led to a crate-within-a-crate setup in which the inner crate containing the object was connected to the outer one by metal springs.
This concept was turned into a structure using computer-aided design (CAD), with finite element modelling conducted in parallel.
To optimize the protective packaging, parameters were defined that could be given a range of possible values within certain limits. These were for example the positions of the springs and their stiffness constants, the geometric dimensions of the inner crate and the materials used. The task of the optimization software was to find combinations of parameters that minimized the dynamic loads the turban snail goblet was exposed to.
The next step was to build the protective packaging described by the data. As the real world is always more complex than the modelled world, collaboration with a professional partner was essential. This was all the more so given that the object would be entering the US, where specific guidelines would have to be adhered to. Bringing in a carpenter to implement the design, as had been done in the previous project, was therefore not an option. To keep the costs down, an existing, proven product was sought that would allow modifications to be made to match the calculated parameter values.
The TURTLE® Climate Cabinet was chosen, a product made by the Dutch company TURTLE® that has been known for 25 years for its high-quality, sustainable art transport crates.
When building the transport crate based on the TURTLE® Climate Cabinet, a protective box was created on polyurethane wheels with low rolling resistance that which could be jacked up onto runners during the truck journeys and the transport on a pallet in the plane. The outer casing was a removable hood with a retractable trolley handle. The hood made sure that packages or side walls nearby would not interfere with the necessary freedom of movement for the inner crate. The inner crate, which was also easy to remove, was mounted in a vibration-isolating aluminium frame during transportation. The inner crate could be carried if required and had passive climate insulation that met the latest standards.
A final detail concerned fixing the turban snail goblet in place in the inner crate. Any inappropriate choices when implementing the transit storage could have negated all efforts to minimize the vibrations. Moreover, the inner crate needed to be sustainable. This meant in particular that packaging waste should be avoided and it should be possible to reuse the protective packaging for other objects.
As a result, the inner space was divided into three sections. The turban snail goblet (without its lid) was fixed in place in the central section using layers of Plastazote foam. The object in its protective casing was positioned in such a way that its median line was aligned with that of the inner crate. The lid was also encased in protective foam and fixed in place in one of the outer sections.
The expenditure on the protective packaging and the courier escort paid off. Unlike other objects, the fragile turban snail goblet returned home to Schwerin in March this year without any additional damage.
The State Palaces, Gardens and Art Collections of Mecklenburg-Vorpommern (SSGK MV) worked together with Professor Kerstin Kracht, a vibration technology & structural dynamics engineer, to jointly develop transport packaging that maximizes vibration reduction and shock absorption in a way that is specific to the object. This minimizes the risk of new damage during transport.
Kerstin Kracht is a visiting professor in the continuous mechanics and material theory group at the Technical University of Berlin (TU Berlin) specializing in the mechanics of artworks and cultural artefacts. She also operates as a freelance engineer in the field of vibration engineering and structural dynamics. For the past 16 years, she has been coming up with new research findings and developing methods to protect works of art and cultural assets from shocks and vibrations. Contact: firstname.lastname@example.org
Katalin Baruth MA was one of the project members responsible for the care of the collection of the State Palaces, Gardens and Art Collections of Mecklenburg-Vorpommern. In that capacity, she escorted the courier transporting the turban snail goblet from the Metropolitan Museum in New York to the State Museum in Schwerin. Contact: email@example.com
A heartfelt word of thanks is due here to Claudia Köhler, the restorer in charge of craft objects and archaeological artefacts at the State Palaces, Gardens and Art Collections of Mecklenburg-Vorpommern, for her invariably cooperative and expert contributions throughout the project. Particular thanks are also owed to TURTLE®, as this transport crate could never have been created without their expertise and extremely high quality standards or their goodwill.