Supporting Old Bones, Storage Jackets for Oversize Dinosaur Bones
Fossil bone can and does break under its own weight without external support. Proper storage of paleontological specimens is as important to their long-term usefulness as is good preparation. One aspect of proper storage is adequate support for fossil bones, which, although they appear strong, lack the internal strength of living bone. This support can include specimens stored within specimen trays, as well as those large or fragile specimens that require more elaborate bedding jackets. For smaller specimens within trays polyethylene foam cut to fit the bone is adequate support. However storage support for large bones, some weighing several hundred pounds, require custom-made support jackets of materials able to withstand the stress of such weight. These are usually Hydrocal plaster and fiberglass with additional supports of metal pipe and wood, lined with polyethylene foam.
The Yale Peabody Museum Vertebrate Paleontology Preparation lab has made over two hundred support jackets for the large Jurassic dinosaurs collected under O. C. Marsh in the 1870’s. This article discusses the design and creation of these jackets, and why this design and these materials were chosen.
Marilyn Fox and Vicki Yarborough
Yale Peabody Museum of Natural History
170 Whitney Avenue
New Haven, CT 06511
Photo Credits: Vicki Yarborough and Marilyn Fox
Fossils stored sitting on their teeth, rocking to and fro within drawers as they are opened, or lying on hard shelving, are often damaged just due to the storage conditions. Old adhesives, such as hide glues, plaster joins, and Duco Cement, fail and the information held within the bones can be lost.
For the very large specimens, we chose to make hard-shell permanent storage jackets. Made from long-lasting materials, these jackets will support the specimens if (when) adhesives fail. We developed this particular style of base because of several factors. One is that we can make them easily, as all the steps are simple. Secondly, all the materials are fairly inexpensive and readily available. Third, the materials are less toxic than some alternatives, although protection should be always worn to avoid breathing MDF (Medium Density Fiberboard), plaster and fiberglass dust. The final and most important factor is that they use the least amount of space in overcrowded collection rooms and still safely support the specimen, while making it available for research.
“In recent years conservators, curators and architects have become increasingly aware of the effects of the environment upon museum collections. We now make great efforts to control such known causes of deterioration as temperature, humidity, light, airborne contaminants, insects and handling. However, we often forget that all objects have weight; and it is this forgotten factor – the ever present effect of gravity – that is one of the prime causes of physical deterioration.” P. Ward, Poor Support, the Forgotten Factor, Museum, 1982
Materials, Tools & Supplies
- 0.1 mil plastic sheeting (local hardware)
- Van Aken Plastalina modeling clay (Dick Blick or local art supply)
- heat lamp to soften clay, and to melt it through a sieve to clean it
- rolling pin
- aluminum foil
- coated steel exterior wood screws, various sizes (local hardware)
- 3/4″ or 7/8″ galvanized steel electrical conduit (local hardware)
- MEDEX or MEDITE II MDF (local distributor of Sierra Pine, http://www.sierrapine.com)
- Hydrocal or Hydrocal FGR 95 (local plaster supply)
- Surform (local hardware) chopped strand fiberglass or heavy cloth fiberglass (Merton’s Fiberglass, or local boat building supply)
- 1/8th” polyethylene foam (local supplier)
- Rhoplex N-580 (Talas – http://www.talasonline.com)
Step 1: The bone is set up in the sand table, in the direction opposite from that in which it will be stored. In other words, mammal skulls are placed in the sandbox teeth down, so that when finally in their jacket, the teeth will be up. Generally, we try to have the most scientifically informative side of the specimen on the top in the finished support.
Step 2: The whole area is covered with thin plastic sheet, to protect the bone from the plaster and clay. The support base will cover all of the bone that needs to be supported but will not extend around the curve of the bone. As much of the bone surface as possible will be exposed and available for research.
Step 3: Van Aken Plastalina Modeling Clay, a sulfur-free clay, is heated to soften, rolled out to the thickness of the 1/8th” polyethylene foam sheet that will be used to line the jacket, and neatly applied over the plastic covered bone. The clay is used to create the shape of the jacket, and is also used to fill any areas that might create undercuts in the jacket.
Step 4: The clay is covered with aluminum foil, to prevent the clay from sticking to the plaster that will be used to create the support jacket. The edge of the foil is where the edge of the plaster will be. The advantage of the foil is that is can be smoothed tightly to the clay, to create a smooth, even surface.
Step 5: Sometimes we add 3/4″ or 7/8″ galvanized steel electrical conduit for added support. This extra structural support is important, especially as we often make open, arched or cantilevered jackets, like this one, rather than creating a solid, and therefore heavy, support.
Step 6: Brown paper can be laid on top of the bone and cut out to make a pattern for cutting the MDF base.
Step 7: The MDF base is cut to shape. We make sure that this base extends outside of the farthest edge of the bone, thus creating a sort of “bumper” for the bone itself. By having the base create the “bumper” we can expose as much of the bone as possible for researchers, while still fully protecting the bone from being damaged through contact with other bones on the shelf. MDF is a compressed particle board, easily worked, but particle boards emit urea-formaldehyde. We prefer to use MEDEX or MEDITE II, which are formaldehyde free boards. Dust masks should be worn when working with MDF.
Step 8: Runners are added with countersunk screws. These raise the platform of the base, so that hands can slide under the specimen to lift it.
Step 9: Here’s the base ready to be attached. In areas where the base is near to and in contact with the bone, we have drilled large holes and screwed coated steel exterior wood screws of various lengths through the base. Both of these help to hold the plaster and fiberglass firmly to the base. Otherwise, the shrinkage of the plaster as it cures could cause the plaster to come away from the base.
Step 10: Either chopped strand fiberglass or heavy fiberglass cloth can be used. Cut into strips, the fiberglass is dipped into the liquid plaster until fully impregnated with plaster, and applied. Excess plaster can be wiped off. The fiberglass should be well worked in so that there are no large air bubbles underneath. The plaster mix can be fairly thin, about the consistency of melted ice cream. Dust masks and rubber gloves should be worn when working with fiberglass. Dust masks should also be worn when working with dry plaster. Rubber gloves protect the hands from drying when working with plaster
Step 11: One layer of Hydrocal or Hydrocal FGR 95 plaster reinforced with chopped strand fiberglass or heavy fiberglass cloth has been added to this base, enclosing the conduit. The fiberglass should be about 1/2” in from the edge. Hydrocal is a very strong gypsum cement. Hydrocal FGR 95 sets more slowly, giving more working time, and is intended for use with fiberglass reinforcement.
Step 12: This base is ready to be plastered on. Working from underneath, the fiberglass is well wrapped around the screws, attaching the plaster of the jacket firmly to the base. Working time and set time of the plaster can be controlled to some extent by adding more or less plaster to the water.
Step 13: Sometimes you really have to get into your work. Here’s Vicki smoothing the plaster. We think the surface should be smooth and clean, partly for esthetics but also to make the jackets less painful to move. The plaster is smoothed, either by hand or with sculpting tools, while it is setting, and can be re-wet slightly with water.
Step 14: The finished and dried base is removed and the edges cleaned up with a Surform rasp. Dust masks should be worn when sanding the edges of the plaster. The plaster needs to be completely dry before the polyethylene foam is applied. A very large may take a week or more to completely dry.
N.B. Some polyethylene foams have been noted to show deterioration of under strong UV light, showing yellowing and brittleness over time. As the citation in the Boston Museum of Fine Art Conservation and Art Material Encyclopedia Online (CAMEO) notes: Ethafoam® is lightweight, stable and has low emission of volatiles although, in general, polyethylene is susceptible to degradation, shrinkage and warping in direct sunlight.
Step 15: Once the plaster is thoroughly dry, the polyethylene foam is applied. We use 1/8th” foam. Rhoplex N-580 is the adhesive. This is an acrylic emulsion that remains sticky, and is used as a contact adhesive. It’s painted on both the plaster and the foam, let dry for about 10 minutes and then the two parts are stuck together. The fossil is not exposed to the adhesive. It is sometimes necessary to cut darts, or slits into the foam to fit a complex shape.
Step 16: The permanent storage jacket is ready for the bone to be placed into it. Usually, we replace the finished jacket onto the bone while the bone is still in the sandbox, and carefully roll both upright. This way the bone is never unsupported and there is less chance of damage.
Step 17: The finished support jacket is relatively light but very sturdy, and will safely support the specimen for the use of future researchers. The base is usually painted white to keep a clean look. The used Van Aken plastilina clay can be cleaned of any plaster bits by melting it through a sieve with a heat lamp and reused on the next jacket.
Images A, B, C These are variations on the plaster and fiberglass support jacket. The wooden base may be lined just with polyethylene foam, as in Image B or it may be a combination of plaster and plank polyethylene foam, as in Image A. Large pieces of foam can be adhered with hot melt adhesive. Image C shows a “clamshell” type jacket, in use at the Smithsonian Institution. These jackets encase both sides of the specimen. One side of the jacket is opened at a time, and the specimen stays safely encased and supported at all times. The use of these jackets requires a large, open storage space and heavy lifting equipment. See: http://www.jpaleontologicaltechniques.org/pasta3/JPT%20N1/Bulletin.html Jabo, S.J., P.A. Kroehler, F.V. Grady, 2006, A Technique to Create Form-fitted, Padded Plaster Jackets for Conserving Vertebrate Fossil Specimens.
Some polyethylene foams have been noted to show deterioration of under strong UV light, showing yellowing and brittleness over time. As the citation in the Boston Museum of Fine Art Conservation and Art Material Encyclopedia Online (CAMEO) notes: Ethafoam® is lightweight, stable and has low emission of volatiles although, in general, polyethylene is susceptible to degradation, shrinkage and warping in direct sunlight.
Jabo, S. J., P. A. Kroehler, F. V. Grady, 2006, A Technique to Create Form-fitted, Padded Plaster Jackets for Conserving Vertebrate Fossil Specimens Ward, Philip. R., 1982, Poor support: the forgotten factor, Museum, 34, pp. 54-56.
Supporting Old Bones, Storage Jackets for Oversize Dinosaur Bones, Fox, Marilyn, Yarborough, Vicki, poster at 2012 SPNHC Annual Meeting, New Haven, CT
A Review of Vertebrate Fossil Support (and storage) Systems at the Yale Peabody Museum of Natural History, Fox, Marilyn, Yarborough, oral presentation given during the Preparator’s Symposium at the 2004 Annual Meeting of the Society of Vertebrate Paleontology, Denver, CO