Authors: Cornelius Palmbach, Thomas Fankhauser, Matthias Läuchli, Anita Hoess und Nathalie Bäschlin
University of Bern /Bern University of the Arts, Switzerland
The number of artworks in transit around the world is constantly growing. During such transits paintings are subjected to a great deal of stresses and risks such as shocks and vibrations. The handling of such paintings at museums, during loading and unloading of packing crates, truck journeys over bumpy roads and cargo handling at airports are typical situations where such risks may lead to the paintings becoming damaged. The objective of the research project (www.gemaeldetransport.ch) is to find a new approach to the classification of the shock and vibration immissions that occur during transit, to the manner in which the associated risks are assessed and to determine tolerances for developing preventive strategies.
The laboratory measurement series carried out using the newly developed simulation rig, together with the supplementary measurements carried out during the actual transportation of paintings, provides the basis for the evaluation of current packaging methods and the development of future ones. The interdisciplinary research team comprises specialists from the Department of Conservation and Restoration (KuR) at the University of Bern BFH / Bern University of the Arts HKB and the Institute for Mechatronic Systems ifms at the Bern University of Applied Sciences in Burgdorf, Switzerland. The project is supported by four business partners: A Swiss insurance company and the four leading Swiss art transportation firms. Specialists from various Swiss museums are participating in the project as partners that are able to contribute practical experience in this area.
Monitoring actual consignments in order to classify the shock and vibration immissions
Until recently an individually assembled, custom measuring system was used for the project, to record the shocks and vibrations acting upon a painting inside a packing crate in transit. This comprises a control unit, an external battery and multiple external acceleration sensors.
This allows continuous, highly accurate measurements to be carried out (with a measurement rate of up to 2,000Hz) over a period of several days (large battery capacity, memory capacity of up to 32GB – depending upon the USB stick used). While this system offers very high performance and precision, it is impractical for the purpose. Firstly, the individual components are very expensive and complicated to use (custom-written application software) and secondly, it is very heavy and unwieldy. It is therefore impossible to pack this system into the crate along with the painting – it must instead be carried in its own technical crate that is connected via cables to the acceleration sensors mounted inside the painting’s crate. An ideal alternative is therefore an
An ideal alternative is therefore an MSR165 logger, configured with an internal triaxial acceleration sensor, internal humidity sensor and an additional slot for a 4GB micro SD card for expanding the memory capacity. This logger still allows continuous measurements to be recorded during transit (without threshold values) over a period of up to 3 days, at a measurement rate of max. 1,600Hz. Reducing the measurement rate allows the maximum operating time to be extended even further. In order to be able to fully utilise the memory capacity of the SD card, the logger is used with the ring memory mode activated. This means that when the SD card is full, the oldest data is automatically overwritten – and therefore deleted. For this reason, the maximum possible measurement time is determined in advance so that the time at which the transport is expected to commence can be programmed as the start criteria and the time at which the memory card becomes full can be set as the stop criteria.
As a result of its very small external dimensions, low weight and the fact that the sensors and power supply are incorporated into the logger itself, the MSR165 data logger can be mounted directly to the frame of a painting or to the inside of the packing crate. It is not necessary to run cables that could constitute an obstacle when handling the packing crate. The ability to easily charge the device’s battery via the USB connection of a laptop and simultaneously program the measurement parameters significantly eases handling of the logger in comparison with the measurement system used previously.
MSR165 allows vibrations in the fabric supporting the painting to be measured
To-date, the MSR165 has only been used to measure the shocks and vibrations acting on the frame of a painting or on the internal wall of a packing case. The device configuration – with its four additional analogue inputs – does however allow a further uniaxial acceleration sensor to be connected so that vibrations in the fabric supporting the painting can also be measured. An additional, self-developed external power supply is however required for this third-party sensor.
It’s not only mechanical influences that can cause damage to paintings; climatic variations present potential risks too. For this reason, a device configuration that includes an internal humidity sensor is used for transport measurements, so that a just a single device is needed to additionally record the ambient humidity and temperature history in addition to the shocks and vibrations within the packing case.
Comparative measurements for evaluating current transportation packaging
The type of painting, the transit route and the mode of transport determine the type of packaging used. From simply wrapping in bubble wrap to the use of an elaborate double insulated packing case, a multitude of methods and material combinations are used in practice to reduce both the number of shock events and the continuous vibrations acting during the transportation of a painting.
An MSR165 was attached to each painting in order to record vibrations the painting were subjected to during the journey over highways, motorways and through city traffic
In order to evaluate and compare the damping power of the existing packaging systems used by the different business partners with one another, test journeys were carried out using trucks with air suspension. Each truck carried up to eight identical test paintings that were packaged differently. This was done to ensure that each of the packaged test paintings was subjected to practically the same stresses. An MSR165 – with the configuration described above – was attached to the frame of each test painting in order to record the vibrations to which the paintings were subjected during the journey over highways, motorways and through city traffic. In order to determine how well the different packaging systems dampened the vibrations generated by the truck, the individually assembled measuring system was used to additionally record the vibrations at the floor and sidewalls of the truck during each journey.
The MSR165 devices were programmed such that recording (at a measurement rate of 1,600Hz, continuous without threshold values) could be manually started and stopped by pressing a button. For evaluation purposes, the recorded measurement data was saved in the form of CSV files and subsequently evaluated using the Matlab software. In order to assess the transmission behaviour of the vibrations from the truck to the test paintings, the maximum values, the RMS level (root mean square) and the dominant frequencies were determined. The results are intended to highlight the pros and cons of the different packaging methods and allow proposals to be developed for optimising them. The further advances and results of the research project can be viewed at: www.gemaeldetransport.ch
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Case study republished with permission in writing from MSR.