What are they and how can they be used in archaeological research?

Wood charcoal is the charred remains of wood used in domestic or natural fires. Anthracology is the study of wood charcoal found in archaeological deposits and can be used to both reconstruct past environments and the usage that populations made of woody plants. This discipline sheds light on several issues of importance to Archaeology, such as the past landscape, dwelling space, site catchment area, fuel economy, use of wood in domestic and ritual contexts, among others. Through this, it allows a better understanding of previous ways of life. Short-lived species can also be selected for C14 dating.

Storage parenchyma is a generic term for various vegetative storage tissues within ‘roots and tubers’ but actually concerns three types of tissues- parenchyma, sclerenchyma and the vascular tissues. Each of these types of tissue has a different function. Parenchyma is thin walled and used by the plant for packing, storage, and turgidity. Sclerenchyma is thick walled and provides cellular support and defence. Vascular tissues include two types of cells:  xylem which is thick walled and for transport, and phloem which is thin walled and also for transport. Analysis of this material can provide information upon the diet and subsistence practices of cultures who utilize root and tuber crops, such as those in the Pacific region.

What is the best way to collect a sample for analysis?

Depending on the research questions being asked, sampling strategies can involve either targeted spot or complete samples from archaeological features such as house floors or postholes, or bulk samples (usually around 10L) taken from archaeological deposits such as midden deposits or other occupation layers. Piha Archaeobotanical Services can advise on the most appropriate sampling strategy.

How can it be extracted?

Charcoal can be separated from samples using either a combination of flotation and wet-sieving, or just wet- or dry-sieving. The methods for extraction should suit the nature of the archaeological deposit and soil composition (for example clay needs to be wet-sieved but sandy soils can be dry-sieved). These can either be done prior to sample submission or by Piha Archaeobotanical Services.

How can it be identified to species, genus or family?

Charcoal identification involves the examination of wood cellular structures visible in snapped or cleaved surfaces under incident light microscopy at 20 to 500 times magnification. Features such as the presence or absence of growth rings, wood porosity, ray size, and the arrangement of vessels can be analysed. Most New Zealand woods have a cell anatomy that is sufficiently distinctive to allow identification to specific or generic level.  

At the most basic level, charred vegetative storage parenchymatous tissues can be distinguished from wood charcoal based on several gross morphological and anatomical characteristics (Hather 1991:673; 1993:3, 2000; Pearsall 2010). These include: rounded shape of fragments and cells, highly reflective vascular tissues and bundles, and irregular cavities caused by the evaporation of moisture. Remains can be identified to a particular taxonomic group if the fragments fit all or most of the features of a reference species such as cell size, shape, the arrangement of vascular tissues, and crystal or starch grain morphology (Paz 2001:82)

What types of samples can I send for analysis?

Bulk or spot samples from archaeological features or deposits, or charcoal that has already been separated.