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Replicas share the sparkle of archaeological discoveries

By: Dr Robin Torrence, Tina Mansson, Category: AMRI, Date: 10 Nov 2017

Skilfully made obsidian replicas enable scientists and communities to benefit from and enjoy significant archaeological discoveries.

Student with replica obsidian tool in Papua New Guinea

Student with replica obsidian tool in Papua New Guinea
Photographer: Rocky Roe © Hargy Oil Palm Plantation

How can everyone appreciate and learn from new archaeological finds once they have been stored in a safe and secure place within the museum? There comes a time when archaeologists must part with the artefacts they have discovered and spent so much time analysing. All heritage items are deposited in an official museum or keeping place so they can be conserved for future generations. In my case, passing material on from my lab to the museum storeroom was especially difficult. This is because the large and beautifully flaked obsidian tools I have been studying over 30 years rightly belong in the National Museum of Papua New Guinea in Port Moresby, the legal depository for all archaeological materials in that country. Once returned to their permanent home, I would no longer be able to share these unique and stunningly beautiful discoveries with specialists and visitors in Sydney.

While facing this dilemma, I recalled a similar situation during my fieldwork in New Britain, PNG. A stunning obsidian stemmed tool was discovered by workmen while bulldozing a terrace for a new house at Barema. Several months after I visited the oil palm plantation to study this key discovery, the manager deposited the artefact in the PNG National Museum. Although conforming to PNG antiquities legislation, he reported that the local community regretted the removal of an important part of their local cultural heritage. He asked if it was possible to make a replica for them. At the time, I had no idea how to help.

Later I wondered if it would be possible to make a copy using a scanner and 3D printer. The problem with obsidian is that it is a natural glass with a shiny surface. The diagnostic reflective surface cannot be captured by scanning. When I posed my problem to Tina Mansson, the skilled model maker at the Australian Museum, she eagerly rose to the challenge. Her brief was to make a model that accurately copied the flaking scars and the sparkle of the original obsidian. Her solution was old fashioned moulding and casting with modern materials, but she used some unorthodox methods because of time constraints.

Tina began by making a mould of the Barema obsidian tool using Pinkysil, a fast setting, two component rubber that copies intricate impressions very quickly. To begin with, she made sure that any dust or fingerprints were removed so they would not be replicated. Next she rolled out a ball of Kleen Klay to serve as a soft supportive base. A snake-shaped length of clay was made to form the positive side of the zip lock. Tina then made a clay wall around the edge to serve as a dam wall and the silicon rubber was poured onto the tool. After it set, the clay was removed, the tool was flipped over onto the other side, and the rubber was coated with a release agent. Finally, the second component of the rubber was poured over to complete the mould. At this stage the original tool was removed. The two part rubber mould then required a pour or entry hole for the resin that would cast the tool along with two or three pin-sized air exit holes to ensure the resin would fill the mould completely.

For the cast Tina used a fast setting, two component, translucent, rigid polyurethane resin called BQueen. It was coloured with a tiny amount of black pigment to mimic the colour of the obsidian. The choice of material solved the patina issue but a further problem was how to increase the weight of the resin cast to mirror the original obsidian artefact. Tina tried adding sand and iron filings to the resin, but both of those dulled the sheen too radically so we had to make do with a lighter tool. Finally, each cast was cured in the oven at 70 degrees Celsius and any excess material or ‘flash lines’ was physically removed.

Tina began testing with an ordinary obsidian tool to check whether making the mould destroyed any of the microscopic traces of use on the surface. Once it was clear that the test artefact was not damaged by the process, she made moulds for 6 tools representing the common shapes among the ancient obsidian stemmed tools, including one with a pecked handle. One of the big advantages of moulding is that multiple copies can be made fairly easily. Tina created 3 full sets of tools as well as a copy of the Barema tool for the local community. In addition to a reference group for the Australian Museum, a set of replicas has been donated to the National Museum in Port Moresby for use in teaching and display. This ensures even when the delicate and irreplaceable originals are safely tucked away in the storeroom, the public can still be dazzled by the shimmery tools with elaborate flaking and complex shapes. A third group went to West New Britain where most of the artefacts were originally found. At the Mahonia Na Dari Research and Conservation Centre they will figure prominently in teaching about local heritage within the Saturday school program for local high school students.

Back in Barema the arrival of the replica tool has been greeted with excitement and it is now proudly displayed in the board room of the plantation. Everyone agrees that a 3 dimensional copy is much better than the photos I had sent them previously.

The current revolution generated by 3D scanning will enable museums to share collections with much wider audiences. Sometimes, however, the plain coloured printed models just do not capture the essence of the original material in a way that can be appreciated by non-specialists. In these situations, old fashioned moulding and casting with modern materials still has an important role to play in sharing the sparkle of important discoveries with a large community of interested specialists, descendant communities, and the public at large.

Dr. Robin Torrence, Senior Principal Research Scientist
Tina Mansson, Production and Design

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