Ammons: Welcome to the Preservation Technology Podcast, the show that brings you the people and projects that are advancing the future of America’s heritage. I’m Kevin Ammons with the National Park Service’s National Center for Preservation Technology and Training. Today we join NCPTT’s Mary Striegel as she speaks with Chandra Reedy. Reedy serves as Director of the Laboratory for Analysis of Cultural Materials in the Center for Historic Architecture and Design at the University of Delaware. Today we are talking to Chandra about the importance of thin section petrography for conservation.
Striegel: Good afternoon Chandra. We’re coming today from the National Conservation Training Center. We would like to talk a little bit about the petrographic analysis course that just took place here. So tell me a little bit about your areas of research.
Reedy: Well, I do thin section petrography of stone and [?] materials, although lately I’ve been working mainly on projects with ceramic materials and working to modernize this technique by bringing in digital image analysis technologies.
Striegel: So, I know you use thin section petrography to study ceramics. Can you tell us what thin section petrography is and how you use it?
Reedy: Okay. For thin section petrography, you have to take a small solid sample from your material. If you have a stone sculpture, you might take a sample from the underside of the base where it’s not visible, and you would never sample a whole undamaged ceramic piece, but when you have shards, which in archeology we tend to have a lot of shards, it’s easy to take a sample as a small slice. Then you mount it in an epoxy resin on a glass slide and grind it down to exactly 30 microns thickness where you can then use the optical properties visible in minerals to identify the material that you have and to also look at different aspects of technology or deterioration.
Striegel: How difficult is it to learn this technique?
Reedy: It is a bit time consuming because you have to learn to identify [?] minerals and you have to be familiar with mineralogy so I learned this at UCLA when I was a graduate student taking geology courses. I took a one year sequence in mineralogy and another in different aspects of stone. But if you don’t have a course like that available, well you can learn on your own, especially if you’re working with a specific type of material. You can really study the components of that material and become an expert in that particular material type.
Striegel: Now I know you’ve received two grants from the National Center for Preservation Technology and Training. How have these grants helped you advance your work?
Reedy: Well the first one was comparing different image analysis packages in their application to cultural heritage issues and that was very helpful for me because I spent a year studying how we can use image analysis and looking at different types of packages and programs in software for image analysis and that helped me in developing that as a new research tool that I can use with thin section petrography.
The second grant was for helping to complete my book on thin section petrography of stone and ceramic cultural materials. It was very helpful in getting to that final completion stage for a book project that took about seven years from start to finish.
Striegel: Well, I’ve seen your book and it has beautiful images in it, and it’s really a useful tool when you’re using thin section petrography. Now what are some the most interesting observations that you have learned from looking at thin sections? What is perhaps maybe a favorite project you’ve worked on?
Reedy: Well, right now I think the one I’m working on right now is one of my favorites. I’m working with the Ancient Ceramic Technology Lab in Beijing at the Forbidden City and we’re collaborating on a project to look at the five great wares of the Sung Dynasty and Chinese ceramics are very, very interesting in general and Sung Dynasty period has some spectacularly interesting glaze technologies and ceramic production technologies, so I’m enjoying that project.
Striegel: Now how do different professions use thin section petrography? For example, how does an archeologist use the technique for say somebody who’s interested in historic architecture?
Reedy: Well, in historic architecture, somebody may be interested in looking at building materials or looking perhaps at deterioration and assessing the results of various conservation treatments to help in selecting the best treatment. Whereas, an archeologist may be more interested in what the technology of the ceramic material can tell you about the people who made and used them or about the different social systems and trade and exchange networks. They may be interested in stone or ceramics in trying to identify a provenance or a source of a material.
Striegel: Okay and how does digital imaging analysis help you with petrography or make petrography easier today?
Reedy: Well it gives you a mechanism for collecting quantitative data over a wide variety of types. You can look at the area percentage of different components and different shape characteristics and size characteristics. You can get in apparently rapid manner, some quantitative data that is statistically valid because you can look at hundreds and hundreds of grains instantaneously. It can also help you in getting better qualitative data because you can use the image analysis to enhance some of the visual aspects that are harder to see just through typical thin section petrography methods.
Striegel: Well I know we’ve just finished up a two-day workshop here where we had ten participants and at the end of that workshop, you asked participants what they learned or enjoyed most about the workshop. Now, I’ll ask you what did you enjoy most about the workshop.
Reedy: Well, seeing people who had never done any thin section petrography before really get interested in it and to begin to see the potential of that technique in terms of the different types of research questions that you can address and understanding how you can get culturally relevant information if you ask the right research questions and go about it in the right way. I didn’t know if people would actually be interested or if they would very soon find it boring or too much in range or just not comprehensible so it was good to see that coming in without much background, they were able to come away with a lot in just two days.
Striegel: Well, I really appreciate you taking the time to talk with us and for being an instructor at this workshop and we look forward to working with you again.
Reedy: Thank you.
Ammons: Thank you for listening to today’s show. If you would like more information, check out our podcast show notes at ncptt.nps.gov.
Until next time, good bye everybody.
More information about training in Thin Section Petrography for Conservation can be found at https://ncptt.nps.gov/petrographic-analysis-for-conservation-2013/