What is your base knowledge about Rare Earth or Neodymium magnets?

Sometimes we just need to begin with the basics.

There has been lots of talk recently amongst conservators about Rare Earth Magnets, specifically rare earth magnets composed of the element Neodymium. These neodymium magnets have gained a foothold as the "go-to" magnet for mounting artifacts for exhibits and display. That is not say that this particular type is the only suitable rare earth for conservators to use, just that our literature indicates it is the most popular choice. Besides Neodymium, the other rare earth magnet for conservators is a Samarium Cobalt.

Rare Earth?  Neodymium? Samarium Cobalt? What do these terms really mean, and is there a big difference from one magnet to another?

To begin with, rare earths are not really rare, nor are they precious. They are actually as common in the earth as lead or tin. What makes them "rare" is that the elements that make up the rare earths are hard to come by, meaning mining for these elements is no easy task, and when they are found, the process to isolate them from the surrounding materials is quite difficult.

On the periodic table they are the upper row of elements that sit below the table (the plum color). (The lower fuscia colored row are the radioactive elements). They are part of the Lanthanide group of elements. Of the four permanent magnets, all developed in the twentieth century, two are made of elements from the Lanthanides; Samarium and Neodymium.

Conservators may be partial to Neodymium magnets for several reasons. They are cheaper than Samarium magnets, but more importantly, Neodymium magnets are strong, compact, permanent magnets, and they have the highest magnetic field strength as well as a higher coercivity (which makes them magnetically stable). The downside is that they have a lower Curie temperature (tolerance to heat  exposure) and are more vulnerable to oxidation than samarium-cobalt magnets. Samarium magnets, are more prone to corrosion and are far more brittle.

So it is an easy choice for many conservators, the neodymium magnet is the logical choice. The drawbacks (i.e your neodymium magnet being demagnetized because it is exposed to high heat) can easily be avoided. Simply do not use hot-melt glue with your neodymium magnet. Other options are available, like countersunk magnets to accommodate a screw for instance.

Hot melt glue and neodymium magnets just don't go together. The temperature of the glue
(even the kind marked "low temp") is just too high and will render your magnet useless.
Neodymium magnets begin to lose strength if heated above their maximum operating temperature,
which is 176°F (80°C) for standard N grades. They will completely lose their magnetization if
heated above their Curie temperature, which is 590°F (310°C) for standard N grades.

So now that we have established why neodymium is the logical choice, lets talk about the variety of neodymium magnets that are available. Not only do they come in a variety of sizes and shapes, but they are available in many strengths as well. Essentially that means these magnets are labeled in a way that tells you how strongly they "stick" to a ferromagnetic surface, which is perhaps the most useful information for conservators as we are often looking for a delicate balance of supporting an artifact, but being careful not to cause any harm to the artifact.

A very small sample of the sizes and shapes of Neodymium magnets available.

Neodymium magnets are marked N35, N38, N42, N52…but what does that mean? According to our favorite magnet distributor, K & J Magnetics, "Neodymium magnets are all graded by the material they are made of. As a very general rule, the higher the grade (the number following the 'N'), the stronger the magnet. The highest grade of neodymium magnet currently available is N52. Any letter following the grade refers to the temperature rating of the magnet. If there are no letters following the grade, then the magnet is standard temperature neodymium".

One of the smallest Rare Earth Neodymium magnets available.   This N52 measures 1/16" in diameter and only 1/32" thick!

The magnet above is an incredibly small magnet, yet as a N52 magnet it's pull force is quite strong.  Finding a balance between size, shape, pull force, and other factors to accomplish a mount is challenging. One would wonder if you could simply weigh your artifact and then figure out how many magnets would hold it up, and maybe add a few extra as a safety feature. But as we all know, nothing is ever that simple. For Conservators it is not just about holding the weight of the object, but how intact is the object, and what is it's ability to hold it's own weight. Sadly, there is no way to measure that. So we build in safety factors, like an angled display board, or a display fabric to provide some built-in friction for a textile.

So often I hear, "oh, magnets?! I know all about those" only to discover that the real magnet knowledge of the speaker is limited, it is only the term "magnet" that is familiar. Understanding that magnets are part of a broad and diverse world is the first step in using them properly.  Being familiar with magnets and their properties is the first part of creating a successful mounting system. In future blog entries we will discuss the other parts of a magnet system: The gap (or space in between the magnet and the ferromagnetic material) and the ferromagnetic material (what the magnet is attracted to).  Once these parts are understood, their cooperation together and the ways in which they can be altered, can be utilized to create inventive and successful systems.
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Gwen Spicer is a textile conservator in private practice.  Spicer Art Conservation specializes in textile conservation, object conservation, and the conservation of works on paper.  Gwen's innovative treatment and mounting of flags and textiles is unrivaled.   Her current research focuses on the use of rare earth magnets in conservation. To contact her, please visit her website.

Learn more about magnets and their many uses in the new publications Magnetic Mounting Systems for Museums and Cultural Institutions. Available for purchase at www.spicerart.com/magnetbook.

Shipping or traveling by air with Rare Earth Magnets

Recently, when I purchased some magnets, I noticed the box that they came in was labeled: "Not packed for shipment by air." What does this mean?

The box was small, only holding a few rare earth magnets in a zip-lock bag and the entire box was filled with crushed paper. I began to think, "what more was needed to ship this package by air"? Is there a concern with the pressure in the baggage compartment of the plane? Could the few magnets in the box effect flight instruments? Neither seemed possible or a significant issue. 

So, I looked into it further. First, I found that magnetized material is NOT regulated as a hazardous material when transported via ground/surface transportation. However, the U.S. Department of Transportation has determined that rare earth magnets pose a safety risk when shipped by air unless they are specially packaged. Many suppliers do not provide such specialized packaging, and therefore do not transport via air. Perhaps they do not want to take the time to concern themselves with the added time to determine this. We know of one trusted supplier who does, to see how they ship their magnets via air, see the link below for K & J Magnetics.

It is important to realize that when groups of magnets are in close proximity to one another, their field forces unify and thus increase. Therefore if a large or moderate quantity of magnets are shipped together, shielding of some sort could be necessary.

Is it safe to take magnets on airplanes? Yes and no. Magnets can affect the navigational equipment on an aircraft. However, most single small magnets are not capable of significantly affecting these instruments from a moderate distance. But to determine exactly how strong a magnet(s) would have to be to affect the instruments, and how close they would need to be to do so, the US Department of Transportation and the International Air Transport Association have set precise guidelines for the transport of magnets by air. If the magnets you are transporting exceed certain thresholds, they will be considered Class 9 Hazardous Materials and should only be placed on an aircraft by trained and certified personnel. 

So, what are the rules?

According to K & J Magnetics,
"There are two important measurements of a package containing magnets. Rule #1: If the field strength is 2 milligauss (0.002 gauss) or more at a distance of 7 feet from the package, the IATA (International Air Transport Association) says the package needs to be labeled as Magnetic (see below). This is especially applicable for international shipments.

This label would be placed on a package containing magnets being shipped via air.

Magnets are often shipped in a steel-lined box to remain below this limit.

If there is any chance that the arrangement of magnets could change, or any package shielding could be damaged so that a measurement exceeds this value, it falls under the Dangerous Goods category and should be labeled as Magnetic.

Rule #2: For any package shipped by air, whether it is labeled magnetic or not, the field strength must be 5.25 milligauss or less at a distance of 15 feet from the surface of the package (FAA Title 49, Part 173.21 Forbidden materials and packages). If the package measures above this value, don't ship it by air.

Why are these rules so important? The magnetic compass. Despite all the fancy GPS navigation systems, the basic compass is still an important part of aircraft navigation. If a cargo of magnets alters the compass readings, accurate navigation might be compromised.

Remember, your magnets are competing with the magnetic field of the Earth, whose strength is only about 0.5 gauss on average."

So the short answer is that a magnetized material is considered a hazardous material and is regulated as a hazardous class 9 material when it is offered for transportation by air and when it has a magnetic field strength that is capable of causing the deviation of aircraft instruments. 

This image from K&J Magnetics shows a packing
method to keep magnets as far from the box walls as possible.

So how do you put this into practice? Well one way is with the use of a compass. That's right that ancient tool that was invented when the mysteries of magnets and Lodestone were first put to use. With your compass you can also measure the field distance of the magnets inside a box. (The first link below also includes a great youtube video showing this!) Remember, the farther away from a magnet you are the more the field force drops.

Read more of K & J Magnetic's article at: https://www.kjmagnetics.com/blog.asp?p=shipping
some other sites to visit:
http://www.rare-earth-magnets.com/t-safetyinformation.aspx

http://www.mceproducts.com/knowledge-base/article/article-dtl.asp?id=10

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Gwen Spicer is a textile conservator in private practice.  Spicer Art Conservation specializes in textile conservation, object conservation, and the conservation of works on paper.  Gwen's innovative treatment and mounting of flags and textiles is unrivaled.   To contact her, please visit her website.

Learn more about magnets and their many uses in the new publications Magnetic Mounting Systems for Museums and Cultural Institutions. Available for purchase at www.spicerart.com/magnetbook.

Ferrous Attractions - What did Conservators experiment with at the AIC Annual Meeting?

In the last few weeks some questions have come up about testing magnetic systems and how to determine the proper system for mounting an artifact. While more and more conservators are turning to magnets (YAY!!!!) as a solution for mounting, there is still some information out there that may be confusing, here I hope to clear that up!

Below is a recap of the hands-on session conducted by Spicer Art Conservation at AIC's 2013 annual meeting. This hands-on session was an opportunity for conservators to test various types of magnets,  ferromagnetic materials (sheet metal, metal strips, embedded washers, etc) and gap materials (the artifact, mylar, display fabric, or other interleaving materials).  

About 80 participants were present for the early morning hands-on session. For those who were unable to attend AIC's 2013 annual meeting, or were at the meeting but were at other specially groups, here is just a quick summary of the session and the important outcomes observed by the various groups. Read the earlier blog post for a full description and details of the materials we used and how the tests were performed. The goal of the session was to become acquainted with the diverse variables of a magnet system. (1. The strength of the magnets; 2. The ferromagnetic materials; 3. The gap or space between.)

Conservators busy experimenting with magnets.

Small groups of 4 – 5 participants were created. Each group had a "jig" (a stand and a combination of a magnet system, and pre-measured weights to test the system with). Any combination of the system could be used. Fabrics, paper, Mylar, etc, were all placed between to act as a gap. Performing each trial 3 times was recommended, and then recorded onto a worksheet.

Wooden blocks were placed on the aluminum bar. Chains were then added to smaller blocks to hang clips. The clip supported the bucket for the weights. All of the weights were pre-measured sand-bags, in sizes of 5lb., 1lb., ½lb., and ¼ lb., as well as ½ oz.

Example of the block on the jig.

Below are images of the various blocks that were provided in each of the five groups. (A detailed description of the different components in each group is in the earlier post - see above for link.)

Local spot fasteners.

Steel gauge

Powder iron in several preparation methods.

Flexible ferrite magnets.

Velcro alternatives. (Read more about this system here.)

Observations

The final section of the session was when, as a group we were able to discuss our observations of the various trials. Each group was allowed to speak. Below are the recorded comments, with some of the most important comments in bold.

Test	Test Comments	Gap Comments
Green	One group recommended, “buy the cup!” While, they also mentioned that it left a mark or impression on the paper.	The felt/batting diminished the strength of the magnet’s strength. This observation represents the whole idea of: the thicker the gap, the weaker the pull strength.
Blue	The powdered iron embedded into the batting created the best results. Groups clearly saw that the increase in the concentration of iron powder held better. The 1” disc magnet in a cup did not hold more weight than the ½” disc in a cup on average. This was seen on all tests.	Mylar on the outside was better than when placed on the inside. This was noticed by other groups too. Nap-to-nap surface was better. Alluding to the fact that friction can play a role in the system.
Orange	The thin foil (.001) steel did not even hold the bucket. (The average weight was 40 grams) 24 gauge steel held the cup	When the Mylar was next to the steel, it failed at ½ lb. where as, when the fabric was placed next to the steel, it stayed at ½ lbs. Other groups also noticed this. Best results were when the suede was between and in the gap.
Red	The overall concession was that Flexible magnets do not hold much weight. One group was able to hold as much as 1-½ pounds using the 0.125 thick magnets.	All felt that the strongest was with the suede in the gap.
Yellow	Not a lot of sheer strength Magnet needs to be smooth when using the cup Mock-up is essential Discussion of how to adjust the lower lip of the “L” slat.	None

Participants quickly found that the amount and thickness of the ferromagnetic material greatly affected the strength of the magnet. This was seen no matter what form the ferromagnetic material was used in: washers, steel sheet, or powdered iron. Neither the foil tape (0.001), nor the powdered iron in the paint medium was found to be strong enough to hold the bucket with any of the magnets. Large differences in magnet size did not affect the pull strength (1” to ½” was the same) (See the table below).

With using a 1/2" disc, N42 grade neodymium rare earth magnet, the table below shows the range of weight values that the range of ferromagnetic materials can support. 

.001 steel	.01 steel	.025 steel	Fender	Thick washer	Painted	Epoxy mix	Embedded batting
Less than 40 grams	½ lbs	1 1/8 lbs	¾ lbs	1 lb	Less than 40 grams	~40 grams	1/8 lbs

The activity was designed as a learning experience while also serving as a fun introduction to magnetic systems. It appears that both were achieved. Participants were able to deal with many of the issues in creating and altering a magnetic system.

While some participants had prior experience with magnets, many were experiencing the magic of magnets for the first time. Many participants mentioned to me their surprise that there were so many magnets to choose from; they had no idea of the differences in size, shape, or strength, or even what a "rear earth magnet" really was. Many participants also mentioned that before the testing they envisioned certain trials to be more successful than others. For example, many confessed their disappointment in the strength of iron powder mixed with paint as they considered it to be a more achievable method for use in their museum and hoped to use that scenario. After seeing the low hold of the iron powder and the risk for slippage of the artifact, many confided that it seemed "too risky".

The other important feedback that came out of the hands-on session was from the conservators in the green group. They immediately saw the benefit of spreading out the "magnetic force" in a system we now call "large area pressure" rather than using an individual point system (i.e. small magnets placed at intervals). Their concerns were based around the possibility of an artifact becoming indented from using a magnet that was too strong. They had only considered mounting an artifact with magnets by placing the artifact on a ferromagnetic backing and simply placing magnets at intervals across its face. Not only did the hands-on session give them appreciation of testing a system before implementing the system, but they realized that they were not limited to using magnets in one single way, instead they could consider having magnets imbedded into the wall, while having a steel strip in the artifact.

The idea of leaving a magnet in an artifact brings up a very important topic. It was not until much later and after much research that we at SAC have started to design systems where the magnet is not kept in the artifact (read an earlier blog post). This is NOT because we determined it to be dangerous (although to our knowledge there is no published information to indicate detriment or safety), but it is really about the cost of magnets and the re-usability of a commodity that currently has environmental concerns (we will not go into it here, but if you are interested, do an internet search on the mining practices for rare earth metals and you will see much of it is done in China, and that it is done in a way that is not friendly to mother earth or the people who call her home).

The use of magnets in conservation is still very much in its infancy, but with good research and sound science, we can make remarkable progress towards utilizing the exciting and great potential magnets possess. Look for more of our blog entries on magnets and conservation in the future, we have a lot to say about magnets and hope that they excite you as much as they do us!

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Gwen Spicer is a textile conservator in private practice.  Spicer Art Conservation specializes in textile conservation, object conservation, and the conservation of works on paper.  Gwen's innovative treatment and mounting of flags and textiles is unrivaled.   Her current research focuses on the use of rare earth magnets in conservation. To contact her, please visit her website.

Learn more about magnets and their many uses in the new publications Magnetic Mounting Systems for Museums and Cultural Institutions. Available for purchase at www.spicerart.com/magnetbook.