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Textile conservator, Gwen Spicer of Spicer Art Conservation at work

Thursday, May 28, 2015

A magnet is only as strong as . . .

. . . . its receiving side will allow it to be.  Yes, that is right, a magnet on its own has no power. But in the company of another magnet, or a ferromagnetic material, it will show its pull force.

Metals are grouped by their magnetic behavior, and this is an important factor in determining a magnet's effective pull force. Metals are divided into three groups:
  1. Ferromagnetics which are very/highly attractive
  2. Paramagnetics which are weakly attractive
  3. Diamagnetics which are opposed to magnetic fields

Magnets used in art conservation, spicer art conservation, textile, paper, object conservator

The magnetic system will not function to its full ability if the receiving component is not properly paired with the magnet. This is because the full strength of a magnet can only be reached if the ferromagnetic material it connects with can become magnetically saturated. This means that the receiving material has to be able to hold all the magnet’s “flux” (i.e. the amount of magnetic field passing through a given surface) to utilize 100% of the magnet’s pull force. 

Of the three metals most often magnetized—nickel, cobalt, and iron—iron alloys are the most readily available. Among all elements, these materials can be temporarily magnetized (also referred to as “soft” magnetization) when in proximity to a permanent magnet. (When positioned near a temporary or “soft” magnet, the permanent or “hard” magnet creates the attachment force). But that attraction is lost once the permanent magnet is removed. One common example is a magnetized chain of paper clips: a permanent magnet touches a paper clip, that paper clip becomes magnetized, a second paper clip touches the first and it also becomes magnetized, and so on. Each paper clip has become a soft magnet, but once a paper clip is detached from the chain, it loses its magnetization.

Steel, composed mainly of iron and carbon, offers a wide range of characteristics including high strength, shock resistance, and machineability. Other metals, like manganese, silicon, chromium and molybdenum, are added to alter the properties of the steel to make carbon steel, alloy steel, or tool steel. However, their addition lowers the ferromagnetic properties of the material.

When a sheet of steel is too thin, some of the magnets strength will extend behind the steel, because the steel isn’t thick enough to hold it all. If another ferromagnetic material is placed behind it, just like a paper clip, it too will be attracted and become a soft magnet. In this way the magnetic field can travel to several neighboring layers of ferromagnetic material, increasing the magnetic force as needed. However, if the sheet of steel is thick enough, then the reverse side of the metal shows no magnetic attraction because the steel has become fully magnetically saturated.

The arrows indicate the alignment within the domain walls

Ferrous metal sheet thickness is measured in gauge, commonly found between 30 (thin) and 8 (thick); therefore the higher the number, the thinner the sheet of metal. Specifically, a gauge 8 metal sheet is 0.4 cm (0.1644 inches) thick; a gauge 30 metal sheet is .03 cm (0.0120 inches) thick. 

Gauge measurement refers only to the thickness of the metal sheet, not to the percent of iron alloy or any applied coating; hence one cannot rely on a specific metal’s gauge to ensure that it will have the intended effect. Galvanizing adds to the thickness of the metal and has its own reference tables. Thus, a 24-gauge steel sheet and 24-gauge Galvanized steel sheet have different thicknesses but are equivalent magnetically. 

When using rare-earth magnets, using 22-gauge or thicker is optimal (the minimum gauge steel sheet to use is 24-gauge). Selecting the best gauge of steel sheet for the magnet system is more critical than the overall weight of the mount.

It is also important that when recording your system that along with the shape, grade and size of the magnet, that the gauge and type of the ferromagnetic material (i.e. galvanized steel) is noted. Without these details the system cannot be fully documented or reproduced.

Gwen Spicer is an art 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 artifacts is unrivaled. To contact her, please visit her website.

Thursday, May 14, 2015

Magnet use in art conservation: charts, tables, references & further reading

Magnets are fascinating, but greatly under appreciated because they are so common in our everyday life, therefore it is assumed that they are simple in function and there is nothing more to know. However, the way they work is really complex and there is so much to know about them. When I mention their use for conservation treatments or mounting for exhibition, I usually hear two different responses:

1)  "I don't use magnets, I don't know enough about them and I'm worried I will harm the artifact, OR I'm afraid the magnet(s) won't securely hold the artifact and it may slip or fall."

2)  "I use magnets! But, I don't know too much about them other than I put the artifact against a magnetic surface and then I put a bunch of magnets on the surface (probably more than I have to, but I want to make sure the artifact won't slip or fall)."

My own use of magnets started when I used them to secure an object to a mount. Truthfully, at the time, I knew so very little about magnets, yet I was keenly aware that I needed to be cautious about using any that were too strong for fear of causing damage. The artifact I mounted was a perfect choice because it was sturdy and there was no risk of crushing or marring any surface. The magnets were placed on the mount with metal washers placed inside of the object. A layer of protective Mylar was placed between the magnet and the object.

When choosing the type of magnet to use for this first project, I knew that some magnets were stronger than others, especially that there were these really strong magnets called "rare earth". I knew magnets needed a receiving material - a metal that they could "stick" to; and that some metals created a stronger "stick" than others. But truly what was physically happening within the magnet or the receiving metal was sort of magic. I needed to understand this magic and I needed to be able to create a mount that was SAFE for whatever artifact I was working with. As I began to understand magnets, I realized that the possibilities were endless; mounting textiles, upholstery work, I could think of so many opportunities where I could employ magnets.

Art conservation, rare earth magnets, textile, object, paper conservator, magnets used in conservation
The tufting of a seat using rare earth magnets.

The next project that was perfect for magnet use was to create the tufting on a chair. Disk shaped magnets were the perfect "button" for the tufting site. Strong magnets made a nice tuft as they were strongly attracted to the washer embedded in the seat layers, and the fabric was a reproduction so there was no risk to harming a textile artifact. When the project was completed I was completely hooked on magnets. I had done countless mock-ups in preparation for the tufting, trying various magnet sizes and strengths, pairing these magnets with various sized metal washers, and determining how the fabric layers in between their junction effected the attraction.

Did I make mistakes in the beginning? Yes, of course. For instance, I had no idea that extreme heat would have an impact on how rare earth magnets functioned. So, in an early project I had the great idea of using hot melt glue to affix foam to the magnet, not knowing that the heat of the glue was too hot and made the magnet useless! How sad to find that I had ruined a few magnets before I realized what was going on.

Rare earth magnets used in art conservation, art conservator, Spicer Art Conservation

Also, if I redid some early mounts, I would have ALWAYS put the receiving metal inside of the artifact, never the magnet. Only because reusing rare earth magnets is more desirable than leaving them inside artifacts because of their cost and the environmental damage caused by the mining of these materials. Also, unless the artifact is clearly labeled "magnet within" (or some other kind of warning), it could be placed too near a metallic surface where an attraction could be made, not a pleasant surprise for the person handling the artifact.

Magnets have been around for a very long time. Articles citing artifacts mounted with magnets appear as early as 1988. These were all important early "pioneer" projects, and as art conservation projects using magnets moves forward in time, the complexity of the magnets and materials grows.

To understand and sort out all of the magnet information I had gathered, I began to create charts to reference information I might need again. The charts are listed below and are linked to the image of the chart itself.

- comparison of types of magnets (and their performance properties)
- a list of art conservation projects using magnets (compiled in 2012)

As I began to understand that there are three parts to a magnet system: 1) the magnet, 2) the space between the magnet and the metal receiving material, called "the gap", 3) the receiving metal; I realized that this was more easily understood if diagramed in a cross section.  Below, are the two most requested diagrams from various projects to illustrate each of the components of a magnetic mount and how they work together.

1) Hunzinger chair tufted with the use of Rare Earth magnets:

Spicer Art Conservation, textile conservator, rare earth magnet, re-tufting of chair, upholstery conservation, restoration

2) Hanging system for textiles using "L" bracket

Mounting artifacts with rare earth magnets, Spicer Art Conservation, textiles, objects, paper

Word to the wise:
There are a few things that I have learned that I would strongly advise when using magnets:

1) Don't use hot melt glue. Instead, read this invaluable information about how to safely glue rare earth magnets from the wonderful and knowledgeable people at K & J Magnetics.
2) Think twice if you are tempted to use the products labelled "magnetic paint" to simply paint a wall and then affix magnets to it to hang an artifact.  While this may seem okay when you test it, mathematically there is just not enough strong magnetic attraction created in this type of a system and because of that simple fact, it would be the most likely system to fail.
3) Fingers get easily and painfully pinched when they inadvertently find themselves between two strong magnets that are "jumping" together. If you are using strong rare earth magnets, keep them in containers where they can be separated and handled one at a time - contact lens cases are PERFECT!

Finally, I have compelled a list containing the references for some books or articles written about magnets, especially the aspects of their environmental impact. I have used many of these as a reference in my papers, talks, workshops, or articles. Additionally if you will find a comprehensive list of my magnet articles they can also be accessed on my website, under the PUBLICATIONS tab.

Also, if you have not picked up a copy, my most recently read magnet book is: "RARE; The High Stakes Race to Satisfy Our Need for the Scarcest Metals on Earth" by Keith Veronese.  Get yourself a copy and read it!

Gwen Spicer is an art 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 artifacts is unrivaled.   To contact her, please visit her website.