Page 283 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

262 Maritime Archaeology: A Technical Handbook, Second Edition
transferred to the sandbox. Slightly more robust material can be placed in a polythene bag filled with water and tied off with a knot so that the bag does not collapse when removed from the water. Large objects are best carried in a basket (such as a plastic wastepaper basket), and commercial fish storage baskets or any self-draining basket of reasonable rigidity is useful.
Usually each operator works in a particular area during one session, so it is best that one operator’s finds are kept together and not mixed with those of other operators working in the same or different areas. By keeping the material together, the excavator can usually provide notes from the record slate or, subsequently, provide verbal information on the objects during debriefing or registration (see Chapter 10). Thus, each excavator must have collection equipment available on the site for immediate use. As the excavator works in an area, important artifacts can be plotted on a plan of the excavation area or grid. Where there is a lot of integrity in the dis- tribution of the material, it may be necessary to take record photographs and detailed plans. In some cases, the objects can be tagged in situ, recorded, and then raised (see Chapter 10 for the problems of tagging).
C. TOOLS
Concretion always presents problems to an excavator because it usually offers no clue as to what is inside. Therefore, it is important to adopt a careful and sensible approach to such objects. In some cases, it is possible to remove the concretion to a conservation laboratory where the material can be dealt with properly and leisurely. If this is not possible, it is impor- tant to have on-site conservation facilities available to deal with the various types of material in their varying conditions. Concretion is a hard, cement- like substance that usually forms around iron objects. The process of for- mation of concretion is not clearly understood, but there are several easily recognizable types. The concretion formed around iron objects tends to enclose the object in a shell that is generally much harder than the object itself. The condition of the object depends on the length of time the object has been immersed under water and the type of iron of which it is composed.
Cast iron, because it has a high carbon content, forms a concretion which exactly molds to the object. The object itself varies in condition as a result of a number of complex processes. Thus, a number of concreted cannon balls from the same area will vary considerably in their state of deteriora- tion without any obvious reason. The outward appearance of the cannon balls after removal of the concretion may be similar; they will all appear to