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Turning a Negative into a Positive (and Vice Versa)

by Bernard K. Means, Director

There are a number of reasons why creating virtual avatars of cultural heritage items is so significant:

  • Preservation: even if the original object ceases to exist due to the marches of time (e.g. decay) or the forces of destruction (mishandling, intentional demolition, etc.), the virtual avatar preserves the cultural item in perpetuity (well, as long as one remembers to migrate the data)
  • Access: virtual avatars can be shared and accessed more readily than the original item to all reaches of the globe (and beyond) via digital means (such as our Sketchfab site), helping to democratize heritage and reducing stress on collections managers
  • Analysis: sophisticated  measurements can be made on virtual avatars of artifacts that would be challenging or time-consuming if analog techniques were used, notably approaches that involve the application of morphometrics to compare data sets
  • Reproduction: Virtual avatars of artifacts or ecofacts can be replicated readily through 3D printing, and used in public programs, teaching, exhibits, and analysis in ways that might be unfeasible or unwise with the original items

To this short and cursory list, I can add manipulation of the virtual avatars using readily available digital tools.

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Terracotta figurines on exhibit in the HNB Garhwal University Museum of Himalayan Archaeology and Ethnography

This past May, I was working with archaeologists at HNB Garhwal University, located in Srinagar (Garhwal), Uttarakhand, India, to help them with 3D scanning of archaeological discoveries, including items that are on exhibit in their Museum of Himalayan Archaeology and Ethnography.  I was funded by Virginia Commonwealth University (VCU)’s Virtual Global Classroom Initiative, so another motive for my being in India was to help broaden access and awareness to this not easily accessible museum, not just for my students but also for people living in India (or anywhere in the planet). Archaeologists Mohan Naithani and Sudhir Nautiyal and I walked through the museum one day during my visit, selecting items that we thought would help achieve this goal.  One of these items was a clay mold for a figurine that dates to the Kushan period.  We had already 3D scanned a number of Kushan-era figurines, and I wondered what the figurine that would have been produced from this mold would have looked like.

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Terracotta figurines on exhibit in the HNB Garhwal University Museum of Himalayan Archaeology and Ethnography

3D scanning of the mold was a bit challenging.  Electrical outages were intermittent as a result of damage caused by a tornado earlier in the week.  It was also difficult to orient the mold in such a way that we could capture the entire interior with our NextEngine Desktop 3D scanner.  Because this was one of the last items 3D scanned while I was in India, I did not know whether our 3D scan of this mold was successful.  I brought this digital file back to the Virtual Curation Laboratory at VCU in Richmond, Virginia, where one of my summer research interns, Wasamah Shaikh, worked to edit this and other models.  Once we created the digital model of the mold, we still did not know how well we had captured the original item, short of producing our own cast from the mold.

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One way to create a cast from the mold would have been to 3D print the mold, and then press clay or some other substance into the mold to see what type of figurine would result. This is not a path I chose, although we can do this in the future.  Instead, I used the freely available program MeshMixer, inserted a geometric shape into the cavity of the mold, and “subtracted” the mold itself (using the Boolean difference option).

2159_scan female mold 13-22_interior

 

This created a positive, e.g. a cast, which revealed the figurine of a woman wearing a necklace. Much as was done 2000 years ago during the Kushan period in North India, we can now mass produce our own figurines.

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I can also reverse the process: make a mold from a positive.  A few weeks ago, I was loaned an architectural detail from Mount Vernon’s New Room that is used in public programs. This architectural detail was made of clay and attached to a board, which makes it a bit unwieldy.

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I 3D scanned the object, and removed the board, leaving behind only the geometric medallion.

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I then 3D printed just the medallion, which is much easier to share with public groups.  I also took the virtual avatar of the medallion and, drawing on the Boolean difference option in MeshMixer, then created a negative of the medeallion, e.g. a mold. This mold can now be integrated into public programs to create replicas using clay or other media in a manner akin to how the architectural detail was created in the first place–using a mold to create a design in plaster. This will enable a more interactive experience for young visitors to Mount Vernon.