Our very own Carolyn Thome will be giving a presentation at the National Museum of Natural History tomorrow. She will be talking about the various techniques used to recreate artifacts including casting and 3D printing. Don't miss it!
The Office of Exhibits Central (OEC) recently launched an exciting new initiative utilizing 3-D scanning and printing technology. One of the projects for which it is being used is an upcoming exhibit on which OEC is collaborating with the National Museum of Natural History (NMNH). For the past several months, OEC model maker, Carolyn Thome, has been working with NMNH model maker, Paul Rhymer, to create plaster casts of bones and prehistoric tools that replicate the original artifacts. The casts will be on long-term display in the exhibit which will be on permanent view at the museum.
In most cases, the plaster casts are being made from artifacts, or from existing casts which the model makers use to create silicone molds from which they subsequently produce new plaster casts. In other cases, objects are on loan from outside lenders who have made their molds available to the model makers for use in making new casts. In some cases, however, neither molds nor casts exist. Additionally, in many instances, the objects are too fragile or too complex, or the artifacts are not accessible long enough for the model makers to be able to produce molds of them. An effective alternative has been to use a 3-D "printer" or "fabricator" to create a cast from a computer data file. The result is a three-dimensional object with an exceptionally high degree of detail.
In order to produce casts for the exhibit using the 3-D printer, the first step in the process was for NMNH researchers Mat Tocheri and Christyna Solhan to scan the artifacts at NMNH using a CT scanner. The OEC team also transported its portable laser scanner to NMNH to help scan objects. Once that was completed, the scan data were uploaded to OEC's ftp site; each artifact had a separate data file. Thome then created a "print build" for each artifact by importing the scan data into the software program and arranging it in the "build envelope" to achieve the most efficient print. The build envelope--outlined on the computer screen--represents the actual size of the cavity in the 3-D printer in which the cast will be created; it measures 15"(l) x 10"(w) x 8"(h). Once Thome achieved the arrangement that she wanted, she forwarded the "build data" to the 3-D printer.
"Print build" showing the scan data for several bones of a Homo floresiensis skeleton
To create the cast, fine powder, similar to plaster dust, is loaded into the cartridge, and an elevator-like mechanical metal plate is positioned at the top of the 15"(l) x 10"(w) x 8"(h) build envelope cavity inside the 3-D printer. To begin production of the desired object, a "fast axis" arm moves back and forth across the metal plate, and spreads a thin layer of powder with every pass; each layer measures .004 mm. Inside the arm, printer heads release a binding agent only where the computer data instruct them to, which binds the powder particles together at those points, creating a solid mass. Each layer has individual print instructions, and successive layers are built up by the slow descending of the metal plate into the cavity, as the fast axis arm deposits layer upon layer of powder and binder. The loose powder that is not glued together by the binding agent, serves to hold the object in place within the cavity. After the object has been removed, the loose powder is collected, and reused for the next project.
Thome finishes the cast by sanding it, and painting it so that it resembles the original artifact, according to the curator's specifications. She then "infiltrates" it with a medium such as epoxy to help stabilize it, and increase its strength. Brackets to position the object while it is on display are then constructed, if necessary. As Thome observed, "Casts, themselves, often become accessioned artifacts, and it is tremendously exciting to be creating these pieces which may become part of the Smithsonian's collections."
An example of the use of this technology for the exhibit is a series of casts, made by Thome, of several bones of a Homo floresiensis skeleton from NMNH's collections, which were scanned by the museum's researchers. The data file for the bones totaled 100 megabytes, and consisted of 39 separate files--one for each bone. Thome processed the data file, and sent the print instructions to the printer. The data file took 11 1/2 hours to print, and had 1,557 layers; the finished three-dimensional cast, standing approximately 6 1/4" high, was then painted and sealed by Thome.
Another interesting example of the use of the technology for the exhibit is a set of casts on which Thome has been collaborating with a museum in South Africa. Because the artifacts were only available for one week, it was not possible for the model makers to prepare traditional plaster casts of them; the use of the 3-D printer, however, allowed the project team to take advantage of the brief window of opportunity during which the objects were accessible. The artifacts were hand-couriered from South Africa to Washington, D.C., where CT scans were made at NMNH. Thome then used the printer to fabricate casts using the resultant data files; the casts included three endocasts--casts made of the inside of a skull; a jaw bone; and prehistoric tools. Thome plans to provide copies of the casts to the museum in South Africa in exchange for allowing their artifacts to be scanned.
3-D "print" of an endocast
3-D "print" of a jaw bone
This invaluable initiative was made possible by a generous grant from the Smithsonian Institution Women's Committee (SWC) which provided funding for the 3-D printer. Their significant gift provided the support necessary for OEC to acquire the equipment, and begin utilizing the technology on current projects. In addition to exhibit work, many other uses for the technology may be developed. As mentioned above, collaborations among museums to exchange casts can increase each museum's respective collection, as well as provide study casts for researchers, thereby creating a significant opportunity for a world-wide exchange of information. Additionally, scan data files can be posted to web sites, greatly facilitating research and analysis.
OEC model makers, Vincent Rossi and Adam Metallo, who brought the 3-D printer to the attention of the Women's Committee, expressed their gratitude to the committee for the SWC's generosity. Due to the Women's Committee's dedication to furthering the interests of the Smithsonian, as well as their understanding of the great benefits that can be derived from this equipment, Rossi and Metallo noted, OEC now has the ability to be able to share this technology with others on an ever-widening range of projects.