Archaeobotany - Storage

PHYTOLITHS : STORAGE

Storing phytoliths

Phytoliths are easy to store. Both the original sediment sample and the silica fraction extracted do not need controlled environmental conditions for their preservation. Storage of phytolith microscopy slides is also rather simple.

The main issue when storing phytolith sediment samples (as when collecting them) is to avoid cross contamination. The samples must always be double bagged using airtight (zip seal) plastic bags. Do not insert the paper label (if one is required) directly into contact with the sediment as paper may contain phytoliths!

Always put the labels in the second bag together with the first sealed bag. Never use paper containers (envelopes, small boxes, etc.) as again they might be a source of contamination. For long term storage it might be useful to first dry the samples in a drying cabinet at ca. 50ºC for a few days to avoid algae growth while in storage, especially if the bags are not going to be kept in the dark. Drying does not damage phytoliths.

This photograph shows different types of vials that could be used for phytoliths storage.

Storing silica fraction for future reference

Once extracted, the phytolith residue can be preserved for any amount of time as dry powder. Sometime they are also preserved in wet form as a suspension in alcohol (ethylene or methylene, but better use the ethylene as it is less toxic). The phytolith powder or suspension can be kept in glass vials of variable volume, depending on how much silica fraction is extracted. In general, vials of between 5 and 20 ml are more than enough for holding the residue but wide-mouth vials are generally better as will make the transfer of the silica fraction in the vial easier (see phytolith extraction). Plastic containers/vials are less ideal because of their high static attraction that will result in the smaller phytoliths to stuck to the container walls. Also, if the silica fraction is stored in alcohol do not use plastic as this will dry up and break in the long run. The vials can be stored in small boxes or vials racks. There is no need to shade light or keep them under specific temperatures.

Storing phytolith microscopy slides

Phytoliths can be mounted in permanent mounting (e.g. Entellen™ or Styrolite™) or in "liquid" mounting using, for example, microscopy immersion oil. Permanent mounting produces slides that can be stored for very long time in special plastic or wooden boxes with slots to accommodate the slides. However, it is important that the slides mounted with permanent mounts that can run are stored in a flat position to avoid possible "running" of the mounting. Indeed, some types of mounting once have dried can still slowly move (run) over the years. For synthetic resins like Styrolite™ this is not a problem and they can be stored in a vertical position. Liquid mounting slides must be stored flat, avoiding putting any pressure on the covers (e.g. do not pile them up) as this will result in oil spillage and consequential loss of the slide.

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