Archaeological Block-Lifting
What I learned at AIC’s Archaeological Block-Lifting workshop for Conservators
At the beginning of March, I attended an Archaeological Block-Lifting workshop in Tucson, Arizona with Dr. Nancy Odegaard and Gina Watkinson. This workshop centred around teaching conservators how to assist archaeologists in protecting objects whilst excavating through block-lifting. This ensures the retention of as much material, and therefore information as possible.
We learned about the situations that create the need for block-lifting materials. This primarily has to do with concerns for the stability of an object. However, it can also be used to:
- Retain the interrelationship between materials
- I.e. a ceramic that still demonstrates contents or retaining the interrelationship between several objects in a deposit
- Demonstrate impressed materials
- I.e. evidence of roofing/matting pressed into clay bricks
- Or to recognise technology and manufacture
- I.e. how wood was joined
This information is essential to understanding archaeological sites and the communities that lived and worked at these sites. The importance of this information requires delicate handling and control of excavation that cannot always be performed on-site and thus, conservators are asked to lift a block of material for precision excavation in a controlled laboratory environment.
Arguably the best part of the workshop was the full day “on-site” at a simulated excavation. On-site, we discussed working with archaeologists and understanding the logistics of blocks after they have been lifted. This includes knowing where the block is going to be stored, how it will be packed (and how the resulting materials will be stored) as well as the reason for the micro-excavation, whether it be for research, drawing, or repatriation. One of the most important logistical questions was that of maneuverability. We had a total of four planned lifts and we were uncertain of their size. We knew that we only had a certain amount of space between the boots of two cars, which would be a possibility in professional applications as well.
On our simulated excavation, we tested varying types of block-lifting methods. This allowed us to understand the need for adaptability on excavation and how certain techniques are more appropriate for specific soil types and climates. Methods also would depend on the strength, size, weight, and condition of the composition of the lift, including both soil and archaeological materials.
The first step was to excavate in our given area in order to understand the limits and depths of the deposit of materials. We determined the spatial aspects of our deposit and began to excavate around the area in order to form a pedestal that we would then support and lift out.
photo courtesy of Paige Hillman
Three different wrapping methods were tested at our excavation:
- Traditional plaster gauze bandage
Plaster gauze bandages were cut into strips and wetted with tap water in order to activate the plaster before being applied to the soil block. The use of several layers ensured that the block was sturdy enough to be lifted.
Pros:
– Most apt for the relatively loose, wet soil and arid climate
– Drying time is reasonable
– Tight wrap-ability around block
Cons:
– Less effective if the humidity were higher
– Issues with access to materials when on site
- Plaster + bandages(+ PVA)
Old Polyvinyl acetate (PVA) glue was watered down and applied to the block to help consolidate the material and hold it in place. Old medical (ACE) bandages were then wrapped tightly around the pedestal. Plaster of Paris is then applied to the surfaces in order to strengthen the block.
Pros:
– Reuse of old materials
– Cheap
– PVA helps consolidate soil around object and limit slumping/loss
– Tight wrap-ability
Cons:
-Messy
– Drying time
– Can be hard to keep bandages taut prior to application of plaster
- Cardboard + expanding foam
Thin, flexible cardboard is wrapped around the pedestal. This is then surrounded by a thick layer of expanding foam in order to push the material flush. This is then further surrounded by another layer of cardboard. After the material is “capped” with a protective layer, expanding foam is applied to the top of the pedestal and pressed flush using a sturdy piece of cardboard.
Pros:
– Useful when considering limited
conservation materials at a remote site
– Cheap
Cons:
– Larger/bulkier materials
– Bad for environment
– Risk for unstable materials
- Methylcellulose and japanese tissues
This technique was not trialed on our simulated excavation. However, it should be mentioned as it is good for smaller surfaces in need of facing or backing. It is primarily used for fragile materials including paint flakes or thin materials without considerable surrounding soil as walls can be built using the tissue to support instead of the soil. This technique can also be altered for water-sensitive materials by using Klucel adhesive in alcohol to replace methylcellulose.
Another variable that was considered when block-lifting was the “capping” material. This is done to further support the block for lifting, as well as protect materials from wrapping materials with a release layer. This is primarily done using either cyclododecane or paraffin wax. There are problems with this practice on site, as both materials require heat to be applicable. Paraffin wax is more widely available than cyclododecane, but its low melting point leaves it less desirable for warmer climates, as it will remain malleable compared to cyclododecane.
After the block is capped and wrapped in one of the aforementioned methods, a thin sheet or tray is used to cut underneath and lift the block. It is then deposited upside down so that the soil can be further stabilised.
One of the main takeaways from this hands-on experience was the importance of problem-solving on-site, between the limitation of materials and time constraints.
The following day, we took our blocks back to the lab in order to excavate in a controlled setting. We discussed the importance of ensuring that there was enough time for the conservator to complete the excavation without stopping in order to ensure the stability of the contents and the knowledge required to assist the archaeologists. It was useful to be able to see the entire process through to completion, as well as enjoyable to discuss finds and potential information we could provide to our fantasy excavation.
Of course, a workshop with Dr. Odegaard would not be complete without some material analysis and spot testing. We utilised spot testing techniques for salts out of Odegaard, 2015 in order to understand the possible concerns for materials once they are removed from their source soil. We learned about the characteristics and tests for four different salts; sulfates, nitrates, chlorides, and carbonates, which we tested on known positives and negatives before comparing them to several unknowns. We were also able to try these tests on ceramics that we removed from our personal block-lifts. We also combined this information with knowledge and testing of water and soil pH, which we learned would help understand further condition issues and assist in recommendations that conservators can provide to archaeologists to ensure the stability of artefacts following their excavation.
This was an incredible experience and I am so grateful I was able to attend and meet conservators and pre-program students from all over the United States. The Arizona State Museum’s facilities are fantastic and it was interesting to further discuss the importance and use of block-lifting and micro-excavations with archaeologists who work closely with conservators. It has certainly reinvigorated my love of archaeology and I cannot wait to be able to utilise these new skills in my professional work.
Thank you to the Foundation for Advancement in Conservation and the National Endowment for the Humanities for individual professional development scholarship, without which I would not have been able to attend this workshop.