November 10, 2014
by Jessica Rymer
Fiske Center conservator Dennis Piechota has been teaching a mini-course on conservation for archaeologists for the past four weeks. Included in this mini-course was a demonstration on excavating and retrieving composite objects, in this case a wood handled iron knife. Listed below are the steps that Dennis recommends for maximum preservation of both the wood and iron during storage and transport from field to lab. Most of the materials that he used in this demonstration can be easily purchased before a project or off-site during one, and assumes that the project has access to a refrigerator. For further reading, he recommends Retrieval of Objects from Archaeological Sites, edited by Robert Payton (Archetype Publications).
1. When exposed to air the wood component begins to irreversibly shrink and distort due to drying – spray wood handle with distilled water if possible constantly to maintain its surface moisture and then cover it with polyethylene whenever possible.
The wrought iron/steel component is also corroding due to exposure to the air. Though it would benefit from being dried and placed in a bag with dessicating silica gel this would destroy the wood component so focus on maintaining the wood moisture first. While the wrought iron component is not stable and will need treatment it is more robust than the wood.
2. Excavate around the object and pedestal it creating a block of supportive soil matrix surrounding the artifact (idea is to then be able to lift the pedestal out and flip it upside down to expose the underside without it all falling apart)
3. Cover the exposed artifact with a barrier film, like a strip of polyethylene. Thin clear high-density poly (HDPE) works well and is often available as trash bags!
4. Apply plaster bandaging (available from art/craft stores) to the pedestal- Lay the wet bandaging over the polyethylene layer so the block of soil is covered on 5 sides (you’re basically making a plaster box).
5. Label the plaster with orientation, context and artifact ID when it is hardened and dried.
6. Slide something thin and stiff under the plaster to lift it out. Aluminum flashing cut to the size of the pedestal works well and is available at hardware stores. Aluminum foil-covered cardboard will work in a pinch especially for small artifacts.
7. Lift and flip the pedestaled artifact while keeping it sandwiched between the aluminum flashing and the plaster support. This will safely put the artifact within the five sides of the plaster ‘box’.
8. You may remove the aluminum flashing to further clean the artifact while supported within its plaster ‘box’ or leave that for the lab.
9. Wrap for transport: Prevent drying by bagging the sandwich of plaster/artifact/aluminum in clear polyethylene e.g., a clear trash bag and wrap the bagged sandwich tightly in clear packing tape. Place it in a refrigerator as soon as possible to preserve moisture and slow the iron corrosion rate.
10. De-oxygenating bags made of Escal barrier film and an oxygen scavenger (available from KeepSafe (http://keepsafe.ca/Prices.htm)) will help preserve the iron while maintaining the moisture in the wood. If you put it in the Escal/O2scavenger bag and refrigerate it, treatment of your composite artifact can wait until the end of the field season if necessary. Without the Escal system the artifact should be conserved as soon as possible.