An Introduction to Magnetic Mounting Systems
At Spicer Art Conservation, we are passionate about magnets and the amazing possibilities of their use in museums and cultural institutions. Their use is especially beneficial where standard stitching techniques are not possible. However the use of magnets is not “magic,” there is actual science behind how a magnetic system functions, incorporating three key factors that must be considered:
1. The strength of the magnet itself. Magnetic strength is the amount of force necessary to pull the magnet straight from the surface of a steel plate. It is measured in Gauss.
2. The receiving ferromagnetic metal, aka, what the magnet will attach to. Magnetized regions of the receiving metal are what allow the full potential of the magnet’s strength to be realized.
3. The magnetic field distance, or “the gap”. This gap is the space created by the layers in between the magnet and the receiving ferromagnetic metal.
Balancing these three parts is what determines a successful system. Once these three key factors are understood individually, as well as how they work in combination with each other, any system can be developed for a specific artifact. No one method appears to be prescribed. Instead each component is adjusted for each particular situation. This is further complicated by the wide variety of needs and requirements of each artifact. Hence, it is only by understanding the parts that make up a system, and their interactions, that a system can be created for a specific task. The developed system needs to be strong enough to support the artifact while not being so strong as to create damage. Each variable can be slightly altered to reach the desired effect. The solutions provided here are to be adapted to fit the needs of the artifacts at hand.
Most museum professionals use the rare earth magnet, Neodymium, due to its small size to high strength ratio. The use of rare earth magnets is still in its infancy, but this will change as the knowledge of how to create magnetic systems is better understood by the community. No one method has been created to support or mount all artifacts, nor should it be. In many ways a “one size fits all” solution is simply too much to ask given the variety and range of artifacts being mounted.
The often-overlooked component of the system is the ferromagnetic material, or what the magnet will attach to. It is the material that the magnet makes magnetic in its presence, i.e. a “soft magnet” or like a magnetized chain of paper clips. The magnet’s performance relies directly on the ferromagnetic material because the magnet will not be optimized if the ferromagnetic metal is not magnetically saturated. Therefore, if a steel sheet or metal foil is used but is too thin, there will be a diminished pull force and the magnet will subsequently behave as if it were of lower strength. The unfortunate part of this is steel is heavy and requires specialized machinery to cut or drill, which is not often found in conservation labs or small museums.
Image of steel gauge on magnetic field and strength with the same size disc magnetic. Image on the left shows a magnet with a thicker steel sheet where the magnetic flux remains within the plate making it a strong ‘soft’ magnet. Where as the image on the right is a thinner steel plate, in which the magnetic flux extends beyond the plate, making it a weak ‘soft’ magnet (K&J Magnetics).
The use of magnets in magnetic mounting systems occurs either as point-fasteners or to provide continuous large area pressure. Both methods have been used successfully.
The local point-fastener, the most common method, uses individually placed magnets. The selection of a specific magnet depends solely on the pull force and interaction of the magnet with the ferromagnetic metal, with no connection to a nearby magnet. The conservator can select a size and grade of magnet for ease of handling; adjust the gap layers between, and design the magnet to blend with the artifact. Magnets can then be added or subtracted based on what is deemed necessary for support. Typically, the artifact is large enough that the magnets used will not be placed close enough to any other neighboring magnets for the polar direction of the individual magnets to be of concern.
A drawback to the point-fastener method is the creation of local stress point in an artifact. For artifacts that have drape, introducing small stresses within the structure can lead to new weaknesses, but for rigid artifacts this approach works quite well. When considering the attachment of a single object to a mount for display, ensure that the pull force is sufficient to support the weight of the object.
The other method for creating a magnetic mounting system is the use of magnets in continuous large areas to create pressure supports to achieve the necessary pressure to hold the artifact in place. This is often done by using magnets with ancillary materials; magnets embedded within stiff materials, an attached webbing sleeve, or some combination of these. How the magnets’ poles are oriented or by their proximity to one another in this auxiliary material will greatly affect the magnetic system’s strength, as well as the selected materials surrounding the magnet. These encased magnetic systems have the added benefit of being reusable.
1. How do you secure a magnet to a mount?
Using glue is a challenge as that it needs to be stronger than the pull force of the magnet that is being secured. This is even the case when a resin, like Acryloid B-48N, that is more attracted to metals is used. But depending on your substrate, strong adhesives like superglue or UV cured adhesive is best.
Actually fastening the magnet to a mount can be done. Some magnets come with counter-sunk holes for a flat head- screw. This method is used by SmallCorp Inc for their Magnetic Slat. Such magnets are secured to an aluminum “L”- shaped strip that actually holds the weight of the artifact, while the strong magnets ensure the hold of the slat to the ferromagnetic material.
The simplest, and perhaps strongest, hold could be the direct connection of a magnet to a ferromagnetic material (i.e. with no gap material in between). This is simply because a magnet attached directly to a ferromagnetic material is more strongly attracted than a magnet and ferromagnetic material with gap material between. A mount where a magnet is placed inside of a metallic cup amplifies this behavior creating an even stronger connection.
What ever method you use, make sure that HOT MELT GLUE is NEVER applied to the magnet! Rare earth magnets will lose their magnetism when exposed to extreme heat. For reference the maximum recommended temperature for a Neodymium magnet is about 500° F. More information about magnets and temperature is available from K&J Magnetics. <https://www.kjmagnetics.com/blog.asp?p=temperature-and-neodymium-magnets>
2. Where should a magnet be placed, on top, inside or behind the artifact?
Part of this discussion is an understanding of care and handling of rare earth magnets for their optimal and continual performance. Areas of concern include the mechanical shock on the magnet, the heat and moisture of the environment, and a demagnetized field. Therefore, systems with a layer of padding material have the advantage of limiting damage to the magnet from the shock of suddenly snapping together, as might occur accidentally during handling when two magnets are drawn together quickly by their strong magnetic force toward each other.
How the practitioner handles the magnet is important. This also is the case with their storage.
A few rules:
Separate the rare earth magnets from all other types of permanent magnets.
Provide cushioning between the magnets and prevent any shock.
Keep away from all heat sources.
Rare earth magnets should be protected. A successful method is to embed the magnet on the mount or within materials. Keeping the magnet surrounded by materials aids in their longevity by preventing demagnetization from both shock and heat. These embedded magnets or ferromagnetic materials can be placed on top or within an artifact as well as being used for the point-fastener or the continuous pressure methods.
Embedding magnets into a stiff material like a mat, or corrugated board is an obvious approach. At the Asian Art Museum, they have mastered the inclusion of camouflaged magnets within an outer border that supports the artifact while on display with the use of a modular system where block-shape magnets are embedded into strips of mat board and become the finishing outer perimeter of the display mount by being placed over the outer edge of the artifact.
3. Should magnets be secured to the mount rather than incorporated with the artifact?
Yes. Probably the most practical reason is that the mount can be reused, and having the magnet positioned in place could potentially be useful. Whereas, if installed in the artifact's internal structure, the magnet might remain there, even after the artifact is returned to storage. The cost of rare earth magnets is ever increasing and the added expense of purchasing more and more magnets is not necessary. More importantly, the long-term effects are unknown; therefore magnets kept within artifacts might be ill advised. Also, keeping an "active device" such as a magnet inside the artifact may cause inadvertent harm. Magnets are always "on", and we at SAC often speak of the "one-mindedness" of magnets and how they will jump to a receiving metal as quickly as possible. If you did not know that an artifact had a magnet inside of it you could place it on, or near, something you actually do not want it to magnetically attach to.
4. How do I learn more about using magnets with my work?
There are many ways to learn more, one can always contact Gwen directly, read her blog posts and of course purchase the recently published book Magnetic Mounting Systems for Museums & Cultural Institutions available at https://spicerart.com/magnetbook/.
Gwen Spicer is a fellow of AIC and as been in private practice for over 20 years. Spicer Art Conservation specializes in the conservation of textiles, objects, and works on paper. Gwen uses magnets for innovative treatments and mounting of artifacts. To contact her, please email her at firstname.lastname@example.org or visit her website where you will find additional information about Spicer Art Conservation and the use of magnets for both treatment and exhibition.
Editor’s note: Magnetic Mounting Systems for Museums and Cultural Institutions won the 2019 Greater Hudson Heritage Network publication award