Archaeobotany - Storage

STARCH : STORAGE

Archaeological and modern reference starch samples can be stored long-term in a variety of forms, including on slides, as dried or alcohol-preserved extracts, or within the original plant tissue (for modern samples). Digital image archives can also be created. The key factor in all cases is that samples are well preserved and protected to minimise degradation and contamination.

Slides

The first thing to consider when curating slides long-term is that some mounting media can degrade starch over time (Piperno 2006; Field 2006). For example, features such as lamellae can become less distinct when mounted in Permount (a non-aqueous media) for long periods. Dry mounts of starch that are rehydrated each time they are examined can also degrade owing to repeated wetting and drying. In some cases, temporary mounts may be preferred so that starches can be removed in future for other types of analysis (e.g. SEM). Semi-permanent slides such as those mounted in aqueous glycerol must be sealed well around the coverslip to prevent dehydration. These types of mounts also remain fluid, so slides should be stored flat so the residue does not shift or leak. Slides should be protected from dust and other contaminants during storage, preferably in plastic slide storage boxes (which can be stored standing upright so that slides remain horizontal) or on trays in special cabinets.

Slide storage cabinet with horizontal trays.

Starch extracts and reference plant samples

Extracts from modern and archaeological samples, as well as unprocessed reference samples (e.g. pieces of root or tuber, seeds) can be dried in an oven at < 35°C or preserved in 70% ethanol (as shown to the right). These treatments will retard fungal growth. Samples should be stored in airtight glass or plastic vials labeled with the relevant sample identification details. Seal labels with cellotape to make sure that they won't come loose over time. If storing samples in ethanol, keep in mind that accidental leaks may cause ink on labels to run, so make laser-printed labels where possible.

Starch reference samples preserved in alcohol.

Digital image archives

Digital photographs of reference and archaeological starch granules are an important data source that can be stored long term with ease. When making a digital archive, it is important that the image quality is good and detail is clear. Always record at what magnification an image is taken and the lighting conditions (e.g. transmitted brightfield, cross-polarised, DIC). If a scale bar is not inserted by the image capture software, then the resolution of digital images should not be modified so that scale bars can be inserted later using another program. It is recommended therefore that a separate copy of all original unmodified digital images be kept as part of an archive. Finally, as with all digital data, back up regularly!

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