Daly Conservation

Otter Tanning Workshop

Cultural Resources Center of the Smithsonian Institution’s National Museum of the American Indian

In May-June 2008 I participated in a otter tanning workshop with Glenn Burlack, a Management Support Specialist at the NMAI and member of the Lumbee of North Carolina, Susan Heald, Head Textile Conservator, Anne Kingery, Catalina Hernandez, and Sarah McNett, Mellon Fellows in Conservation, Ashley Jehle and Kari Kipper, pre-program interns in conservation, and Monique Tyndall, a Mellon intern in conservation at the Smithsonian Institution’s National Museum of the American Indian Cultural Resources Center in May and June 2008.The purpose of the workshop was to demonstrate one method of tanning, synthetic tanning or syn-tanning.

In ethnographic conservation we deal with many tanned skins and hides, by going through the tanning process we obtained a better knowledge of how it chemically and physically changes the skin so it is soft, pliable, raises the shrinkage temperature, and makes the skin less sensitive upon contact with water.

Glenn has been trapping for 30 years; he learned trapping from old time trappers in Slickville, Pennsylvania. He began trapping opossums and raccoons in the woods. He has been brain-tanning for around 20 years, and over the past five years he began using a synthetic tanning process. Swamp trapping is not as popular as it once was due to the decline in prices in the fur market and many swamp trappers are retiring. To counteract the decline in beaver trapping the Department of Natural Resources has raised the limits to how many otters you can trap from 5-per season to 10-per season[1].

The limit on otter was raised because in areas with severe beaver problems swamp trappers were reaching the otter limit and leaving[2]. Otter and beaver are both aquatic furbearers if you are trapping in an area where both live you could trap either in your trap. The season for trapping beaver and otter is December 15-March 14 in Maryland for 2008-2009[3]. The maximum penalty for going over the bag limit, the limit on the number of otters you can hunt per day or season, is a fine of $1,500.[4]. Otter and beaver are trapped in the winter when their coat is thick and holds together more after tanning.

We tanned river otters, species Lutra canadensis. Otters are around 2 ½ feet long and weigh 11-24 pounds[5]. Otters are recognized as one of the more intelligent species.[6] They are different from beavers in that they do not build a community but travel up and down the rivers and mate with multiple partners[7]. Glenn trapped the otters in the Zachia Swamp in Southern Maryland. He uses un-baited body gripping traps placed under the surface of the water. Once the trap has been triggered, the set-up breaks apart from the thrashing of the animal in the trap and goes downstream. The trap is connected on one side by 4-5 feet of wire which are anchored into the ground. Since the trap goes downstream other otters are not alerted to the presence of a trap at that particular set-up.

Glenn “clean-skinned” the otters before we began the tanning process. Skinning refers to physically removing the skin from the body. Fleshing refers to removing the residual pieces of fat, connective tissue, membrane, and muscle that are still on the fur after skinning. Clean-skinning is removing the skin and as much of the fat and connective tissue as you can in one step. It is a more detailed skinning because it is all knife work. It is not possible to merely pull the hide away to separate it from the connective tissue and fat. Skinning and fleshing otter is more involved than some other animals because there is little to no fat tissue. Trappers used to skin on the trap line, but now they skin the next day. This ensures that the body is cold and the trapper will not be exposed to rabies.

We decided to follow a synthetic tanning process. Synthetic tanning was first manufactured in 1911 in Germany.[8] We decided to use a synthetic tanning process for the otter; as they do not have a sufficient amount of brain per animal to perform brain-tanning. We decided to follow a pit tanning process rather than a drum tanning process. Pit tanning is a more traditional technique using organic tanning chemicals in a large bath and manipulating and breaking the skins by hand. Drum tanning is much quicker than pit tanning because the mechanical action of breaking the skins is performed in the drum. However, the mechanical action of the drum can damage the grain surface of the skin.[9]

When we began the five clean-skinned otters were very stiff. We soaked the skins in water and liquid dish soap to soften the fats and make the skins more pliable. After rinsing we placed the skins in an acidic bath with salts and a de-greaser, this process is called pickling. The pickling uses Citric Acid to make non-structural proteins like fatty tissue soluble so they can be removed. By removing the non-structural proteins the tannins will adhere to the structural proteins more successfully[10]. The addition of a degreaser is important when tanning otter because they have high oil content in their skins and many problems arise if the oil is not removed.[11] We agitated the skins every day using a stick, after a few days we removed the skins from the pickle, placed them on a fleshing board, and removed more fat and tissue with a draw knife. The skins were then put back into the pickle.

The skins were removed from the pickle and rinsed, then neutralized with a baking soda and water bath (Sodium Bicarbonate) and rinsed again. It is important that the skins are neutralized or the tanning chemicals will rapidly fix to the skins surface with little or no penetration[12]. This causes the interior of the skin to become stiff on drying as result of grain collapse because the tannins did not penetrate the skin fully.

Next we prepared the tanning solution and left the skins in the solution for about 24-hours. The tanning process forms cross links between collagen fibrils in the skin and stabilizes the fiber network structure by tying up the reactive sites on the collagen molecules. It fixes the ionizable side groups of collagen by increasing hydrogen bonding between collagen molecules[13]. This prevents deterioration and raises the shrinkage temperature of the skins, which could be correlated with the reduction of water in the fibers.[14]

After tanning we oiled the skins with Pro-Plus tanning oil. The oil was applied with a brush and the skins were left overnight so the oil could penetrate the skins. The skins were then broken over a blunt edge. A fleshing board and a hockey stick were used to stretch the skins and make them more flexible.

The workshop gave me insight into the lives of otters, the culture of swamp trapping, and how the collagen fibers are broken down chemically in the tanning process and physically in the breaking process. I saw the important service swamp trappers perform to keep populations of animals like beaver and otter, which can be destructive, balanced. We had five otter skins to tan and this provided enough work for eight people during the pickling, tanning, and breaking. Breaking the skins is labor-intensive and I was glad to have so many people to help with that part of the process. I found that performing traditional processes gave me a greater reverence for the objects in our collection and the work that was required to make these objects. As an ethnographic conservation student this is invaluable to understand the importance of the fur or skin I am treating.

Rose Daly

Pre-program intern in Conservation

The National Museum of the American Indian

Photographs taken by workshop participants

---

 

[1] http://www.dnr.state.md.us/huntersguide/furbearers.asp

 

[2] Phone conversation with Robert Colona, Furbearer project leader for the DNR. 6/26/08

 

[3] http://www.dnr.state.md.us/huntersguide/fbchart.asp

 

[4] Phone conversation with Sgt. Ken Turner Spokesperson for the MD Natural Resources Police. 6/24/08

 

[5] http://www.mnh.si.edu/mna/image_info.cfm?species_id=142

 

[6] http://www.nationaltrappers.com/otter.html

 

[7] Personal conversation with Glenn Burlack 6/2008

 

[8] http://spotlight.satra.co.uk/linkfiles/Spot1207-Modern%20leather%20manufacturing.pdf

 

[9] Michael, Valerie. The Leatherworking Handbook: A practical illustrated sourcebook of techniques and projects. Orion Publishing Group. March 2006.

 

[10] http://www.vandykestaxidermy.com/newsletter/dec08-2004.htm

 

[11] http://www.vandykestaxidermy.com/tanning-hair-on-hide.php

 

[12] http://www.vandykestaxidermy.com/newsletter/dec08-2004.htm

 

[13] http://dhr.dos.state.fl.us/museum/collections/artifacts/acs4/

 

[14] N.C. Avery and A.J. Bailey. “Restraining Cross-Links Responsible for the Mechanical Properties of Collagen Fibers: Natural and Artificial”. Collagen: Structure and Mechanics. Springer US. May 2008.

More Links:

U.S. Department of Agriculture directions on home tanning 1962

Tanning Deer Hides and skins from New Mexico State University

Patent for Syntan: the method we are using

Syntan