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Textile conservator, Gwen Spicer of Spicer Art Conservation at work

Tuesday, April 24, 2018

Successfully Mounting Barkcloth with Magnets

A few months ago I was fortunate to have a visit with Monique Pullan, a conservator of organic artifacts at the British Museum. I was interested in seeing how she was mounting a range of artifacts using a magnetic system, and I was especially curious to talk with her about mounting barkcloth, which has long been a challenging material to display safely.

First, what is Barkcloth?

"Barkcloth is a versatile material that was once common in Asia, Africa, Indonesia, and the Pacific. Barkcloth comes primarily from trees of the Moraceae family, including Broussonetia papyrifera, Artocarpus altilis, and Ficus natalensis. It is made by beating sodden strips of the fibrous inner bark of these trees into sheets, which are then finished into a variety of items. Many texts that mention "paper" clothing are actually referring to barkcloth."    -- Wikipedia, accessed February 24, 2018

Making barkcloth

Given the fibrous nature of the material and methods of fabrication, barkcloth is often characterized by creased surfaces, undulating edges and irregular sizes. It is used for clothing, for masks and various ritual objects, to support painted decoration and to mark sacred spaces. Write Nicholas Thomas and Jonathan Watkins, "... barkcloth formed a major vehicle for creativity, kinship, exchange, and the expression of political prestige. Everywhere these fabrics maintained and communicated the artists’ deep connections to ancestors and country." [1]

As you can imagine there are large collections of barkcloth in museums ranging in date from the early nineteenth century up to the present day. Also called Tapa cloth, they are important culturally, symbolically and historically, but are often collected for their sheer decorative appeal.

Mounting with Magnets

Barkcloth has long been a challenge to mount in museums due to its wide variety and difficulty of fitting it within standard mounting museum methods. For one, is it a textile or paper? Actually, neither of these fully describe the nature of this material. Conservators have in the past generally mounted barkcloth as though it was a textile, using Velcro, sleeves for rods, hinges or even Plexiglas clips in an attempt to find a suitable method to support these widely varied materials.

As one can imagine the possibilities of using magnets is now an increasingly viable option. What has become clear in researching magnetic systems for mounting barkcloth with magnets, however, is that few systems have been published. The few systems that have been published do not fully describe the system such that could be fully reproduced.

Part of the reason to visit Monique Pullman at the British Museum was to see she how she has mounted barkcloth in their collection. She showed me a method were she attached a 'magnetic' stainless steel sheet to a Tycore (honeycomb archival paper board) mount. The full mount was covered with flannel and display fabric (for information about 'magnetic' stainless steel see our recent post 'What is magnetized stainless steel?'). The fabric-covered, disc-shaped N42 grade magnets were positioned along the upper and side edges of the barkcloth, as shown below. The outer surface of the magnets were covered with toned Japanese tissue paper (more can be read about camouflage of magnets by reading 'How do I camouflage my magnets?').

Cross-section of the magnetic mounting system used by Monique Pullman and the British Museum (left);
Schematic showing the location of the individual disc-shaped magnets along the upper and side edges.

Monique Pullman's mock-up board for her
magnetic system for mounting Barkcloth.

This is only one of the many variations of magnetic mounting systems that have been used and that I have documented. A summary of all of the systems found at this time is that they are all 'point-fasteners', in essence where single individual magnets, either disc- or block-shaped, are used with a receiving metal.

In studying the magnetic systems used, I have been interested in the spacing and location of the individual magnets, the weight and thickness of the barkcloth, the grade, size and shape of the magnet, as well as the type and gauge of the receiving side metal or the ferromagnetic material, whether stainless steel or steel. All of these details are important to gather in order to replicate the mounting system or to even develop a possible 'rule of thumb' to mount an artifact as varied as barkcloth.

In my forthcoming book, Magnetic Mounting in Art Conservation and Museums, many magnetic mounting systems are illustrated to mount barkcloth and other types of collections -- with an attempt to present systems that can offer solutions to meet the variety of types of cloths that can be found in museums.

[1] Nicholas Thomas and Jonathan Watkins. Tapa: Barkcloth Paintings from the Pacific. Exhibition Catalogue, Ikon Gallery, Birmingham, UK. 2013.

Additional Resources
Kimberly Adams. World in Progress: Modern Bark cloth in Uganda. Deutsche Welle. (2016-01-27). 2016-01-28.

Margot M. Wright (ed.). Barkcloth: Aspects of preparation, use,deterioration, conservation and display, 96-111. London: Archetype Publications. 2007.
Peter Mesenhöller and Annemarie Stauffer (eds.).  Made in Oceana: Proceedings of the International Symposium on Social and Cultural Meanings and Presentation of Oceanic Tapa. 117-28. Newcastle on Tyne, Cambridge Scholars Publishing. 2014.

UNESCO. Bark Cloth Making in Uganda. 2005.

Wednesday, April 18, 2018

Hands-on magnet experiments that look closely at particle size

One of my local museums, MiSci, in Schenectady, New York, is a popular hands-on science oriented museum. During my last visit, I was greatly surprised to find a small exhibit with strong magnets that tested the attraction of various iron particle sizes. The exhibit consisted of three vessels filled with liquid (see photo below); at the bottom of each vessel were particles of iron. Each of the three vessels held a different size of iron particles, starting with a "nano" size. Positioned near the vessel were two magnets on vertical sliding rods.

Three vessels with magnets on rods. Each vessel contained different sized
 particles of iron, yet the magnet near each vessel was the same size and strength. 

The purpose of the exhibit was to learn how the particles behave in the presence of the magnet. For the interest of conservation and understanding more about iron particles, this was a wonderful activity to see!

Below is the image of the iron particles that are considered "nano" size or 100 nanometers or 0.1 microns. In the presence of the magnet, the particles are all clustered together very near the magnetic field. As the magnet moves up the vessel the particles stay together following the magnet and traveling easily together in a tight group.

The image below shows a larger size particle, called "magnetite sand" at 1,500,000 nanometers. These particles followed the magnet as it moved up and down on the rod, but did not remain as a tight group. These particles are so small they have fewer magnetic regions that can align to be attracted to the magnet. More about domains can be read in a previous blog post "Magnets are only as strong as ....".  

Next is "magnetite powder", at 3,000 nanometers. These particles only slightly are attracted to the magnets. These particles are hardly attached to the magnetic field force. They really just want to sit at the bottom of the container.

So, what is going on here? What might be the difference between "sand" and "powder"? Clearly it is the activity of the small regions, even smaller than the particles called "domains". It is how these domains align in the presence of a magnet that make them attach to a magnet or not.