Encapsulating Support for Large, Three-dimensional, Fragile Specimens
This system allows the specimen to be safely stored and, when necessary, turned over without handling the specimen itself. It also allows hoists and lifts to be used when turning large or heavy specimens without damaging them.
Dan S. Chaney
Department of Paleobiology
National Mus. of Natural History
Washington, DC 20560 USA
Tel (202) 357-4479
Fax (202) 786-2832
Photographs: Karen Ackoff
& Britt Griswold
Illustrations: Alexia S. Scott
The support consists of two or more pieces constructed of strong, lightweight materials such as polyester resin or gypsum cement, and glass fiber (Fig. 1).
Figure 1. top, Shell base has been removed to view encapsulated specimen in support.
bottom, Shell base removed from specimen.
The support is constructed as a form on which the specimen can be stored for extended periods of time (see also Fitzgerald et al., “Storage System for Large Objects Using Form-fitted Support Pallets and Pallet Racking,” this volume).
Each of the support parts has wide lips that are fastened together with bolts, nuts and washers so that they do not separate when the specimen is turned from one side to the other (Fig. 2), but can be separated to view the specimen (Fig. 1). Metal legs, supports, or braces may be added as required to the basic support.
Figure 2. Support is turned upside down prior to viewing. Wooden braces have
been incorporated into support shell base and casters to ease movement of specimen.
Electrical conduit is used to strengthen the top half of the shell.
Materials Tools Supplies
- Container, large, flexible for mixing gypsum cement
- Casters, metal
- Electrical conduit (optional)
- Glass fiber mat, chopped, and polyester resin or glass fiber mat continuous strand, random monofilament , 15mil and gypsum cement
- Paintbrush, for applying resin
- Polyethylene sheeting
- Polyvinyl acetate, 20% in ethyl alcohol or acetone or ethyl methacrylate/methyl acrylate copolymer, 20% in acetone
- Scissors or utility knife
- Stainless steel metal bolts and wing nuts (size dictated by size of the support)
- Stainless steel strips with pre-drilled holes
- Stainless steel washers (size dictated by size of the support)
- The specimen is prepared for storage and the procedures for construction of the first section of the support are described by Fitzgerald et al.”Storage System for Large Objects Using Form-fitted Support Pallets and Pallet Racking,” this volume, in steps 1 through 5 under Customized half-shell forms. In this discussion, polyester resin and felted chopped glass fiber mat are used to construct the support.
Working with polyester differs from working with gypsum cement in that much greater ventilation is needed because of fumes, and the glass fiber mat is always placed on the specimen and then coated with polyester using a brush.
- Construct a wide lip around the specimen by fashioning a temporary dike from cardboard or clay to support the polyester and glass fiber mat while it cures (See Chaney et al., 1989). Notice that the lips are at right angles to the specimen whenever possible (Fig. 3).
Figure 3. Setup for construction of the support shell. Polyethylene sheeting
provides a vapor barrier and separating layer for support shell.
The proper positioning of the lips is needed to prevent the specimen from becoming locked into the support. It is important that only half of the specimen be covered by one half shell; the lips should never be positioned lower than the middle of the specimen. Temporary cardboard or clay dikes must be used in constructing the necessary number of support parts.
- Continue with steps 6 through 12 in Fitzgerald et al., this volume. Do not trim the polyethylene sheeting vapor barrier as it will later be used as a separator between two adjacent sections of the support (Fig. 4).
Figure 4. Cross section of completed support. Note separating layer.of poly-ethylene sheeting, metal reinforcing
strips, and wood brace.
- When the first section of the sup-port has cured, turn the support over with the specimen in it.
- Move the polyethylene sheet vapor barrier aside and coat the lip with polyvinyl acetate or an acetone soluble acrylic resin, to prevent the lips of the next section to be constructed from sticking to the lip of the finished piece. The finished lip will serve as the support for the construction of the lip of the second part.
- Cover the exposed remainder of the specimen with polyethylene sheeting and continue with steps 6 through 12 (Fitzgerald et al., this volume). If there are more than two pieces of the support to be constructed, repeat this step as necessary. do not remove any pieces until step 7 has been completed.
- Add metal reinforcements to the lips when initially made, or after all the pieces of the support have been completed. Metal washers need not be incorporated into the lips of small and medium sized supports. Longer and stronger reinforcements should be incorporated for ease of use at a latter time (Fig. 5).
Figure 5. Top view of support showing metal reinforcing strips.
When using washers, bolts, and nuts to hold the pieces of the support together, drill holes slightly larger than the bolts through both adjoining lips. Space four or more holes to provide sufficient closure. Place one washer on each bolt prior to insertion into the holes and a second washer over each bolt prior to screwing on the nut. This distributes the force of the bolt head and nut and avoids breaking the lips. Finger tightening of wing nuts is sufficient.
Alternatively, one can use strips of metal with preset holes for easy alignment of the two pieces. Fasten the ends of the metal strip into the lip by placing glass fiber strips across them and applying polyester resin to adhere them to the lip. If the metal strip is long it may be desirable to fasten the middle of the strip to the lip in a similar manner.
After attaching the metal strip to one lip, drill holes through the adjoining lips using the holes in the metal strip to determine their location. Place bolts through the holes in the metal strips and through both lips. Then place the second metal strip for the other side over the bolts and screw on wing nuts to hold the metal strip in place. Then fasten the second metal strip to the lip as described above.
- With the bolts and nuts in place holding the two sections tightly together, the specimen may be turned with either side up (Fig. 2). The upper support may be removed by removing the nuts and bolts and carefully removing the support.
To view the other side of the specimen, carefully replace the support, insert bolts and nuts, and tighten with fingers. Turn the specimen over in the supports, remove nuts, bolts and support section. The specimen need not be touched during this entire process.
Gypsum cement and monofilament glass fiber mat can be used to construct supports for small to large specimens. Heavy, and unusually large specimens are better supported by polyester resin and glass fiber mat.
There are no set guidelines as to when to use gypsum cement or polyester. Familiarity with the product and the individual requirements of each specimen will determine which materials to use. The polyester resin, however, produces a lighter support.
The type of steel reinforcements will vary with the object. For small supports, metal washers usually are sufficient to spread the load. For middle-sized projects, flat metal strips with holes can hold the bolts if they are lined up properly.
Support forms for large specimens will require additional bracing of the support itself. These braces can be made of wood or metal and are incorporated into the support to form a flat base (Figs. 2, 4, 6).
Figure 6. Bottom view of support showing wood braces for stabilization.
The ends are fastened to the support just as are the metal strips on the lips. Much more glass fiber and polyester resin are required to assure that the braces do not break off at any time.
It is important to be able to inspect specimens easily to monitor them for signs of deterioration. The upper support must be removed each time the specimen is examined. After removing the support, place it next to the specimen just as it was removed, or flipped it in its mirror image, thus preventing confusion when replacing it.