Lifting Techniques for Retrieving Artifacts from an Excavation
There are many considerations essential to minimizing damage to deteriorating artifacts upon their discovery during an archaeological excavation including preparation, cost, time, and minimizing the effects of surrounding features of a site. Archaeological conservators collaborate with others involved in the methods used for processes of conserving significant organic and inorganic materials determined to need specialized care. The early stages of preparation and retrieval of objects from a site can set the stage for the degree of impact and damage to them; improper retrieval can severely damage objects and it is critical that conservators recognize that in some cases, the best option is to leave objects in situ.
There are several lifting techniques used by conservators that, if prepared and performed correctly will provide safe storage and transportation of fragile artifacts until they can be properly excavated, analyzed and curated in a laboratory. The methods for lifting from a terrestrial excavation, are block lifting objects isolated in situ on a platform and lifting objects that have been isolated on a pedestal; they have been developed as a means to provide support to prevent fracturing and further deterioration of cultural materials. Prior to using any lifting technique, it is imperative that all preparation steps have been set, including having all materials and assistance necessary for a successful excavation. If the conservator cannot attain the required materials and assistance, then they should not engage in any attempts to retrieve an object. In a case where the situation calls for rescue archaeology techniques, improvisation with materials on-hand may be necessary. A reasonable assertion is the most crucial component to lifting an artifact is a thorough preparation. It should be noted that with future technological advances, techniques for artifact conservation will likely improve and lifting methods will also change. Additionally, the method chosen is determined by the condition and type of artifact and should be the least intrusive to the object itself as well as the context of its immediate surroundings within the archaeological excavation.
The method of block lifting involves lifting an object from the ground. First, the surrounding upper and lower parameters of the block must be determined. The object is isolated in situ on a soil platform with enough soil to sustain the integrity of the object. Second, the soil environment the object has resided in must be maintained as much as possible to minimize damage; in the case of moist soils, the humidity is retained by misting the soil with water and then covering the entire block in a protective covering of gauze bandages. Third, the bottom of the block is undercut with a trowel and then a strong, firm support slid underneath the block. Finally, the block can be further protected with additional bandages and/or other safe protective materials, and then removed and placed into a proper storage container.
Methods for lifting objects isolated on a pedestal are similar in that they both require parameters for removal to be delineated, and objects to be pedestaled and protected by some kind of supporting material. Their differences lie in the types of supports and materials use. One method is referred to as “lifting from a cocoon” (Cronyn 1990:47) where the object is isolated on a soil pedestal where the object may be partially exposed. Next, the soil can be misted with water and both the object and pedestal wrapped in damp non-acidic tissue. Then the object and pedestal are wrapped in gauze bandages that have been soaked in plaster of Paris. Once the plaster of Paris has set and hardened, the cocoon can be removed from the ground by undercutting with a trowel then sliding a firm support underneath. The cocoon can then be inverted and placed in a proper container. Another method, referred to as “Lifting by the formation of a polyurethane foam cocoon” (Cronyn 1990:49) involves isolating the object on a soil pedestal and wrapping it in some kind of “clingfilm.” Next, a rigid support such as corrugated cardboard is set in place around the object. The cardboard must be supported by surrounding soil banked up against it. Then polyurethane foam can be poured in according to directions and allowed to set. Once set, the cocoon can be covered and stopped with a plywood lid, and removed from the ground as in the previously discussed methods. The cocoon is inverted and placed into a proper container.
Other similar techniques used vary in the kinds of materials used to protect fragile objects. The primary focus is for conservators and people they collaborate with on a given project to carefully determine all the necessary preparation, materials, methods, and available assistance required to ensure minimal damage to objects. If these steps are unattainable, or an object cannot be safely excavated then retrieval must be postponed until circumstances provide for a safe retrieval.
Cronyn, J.M. 1990 The Elements of Archaeological Conservation. London: Routledge.
Prince of Wales Northern Heritage Centre 2007 Conservation Manual for Northern Archaeologists, 3rd ed. Rosalie Scott and Tara Grant, eds. http://www.pwnhc.ca/programs/downloads/conservation_manual.pdf, accessed February 23, 2014