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the Trust’s very own flotation tank

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This week, Trust excavator Emma Sanford was busy at Roman Circus House making a flotation tank, assisted by Trust renovation volunteer Neil. The tank was set up in the yard and in full working order on Wednesday (20th May). The Trust’s flotation tank is special, though, because it incorporates a vintage pump which we retrieved from the rear of the former Radcliffe’s shop in the High Street at Colchester, during our excavation at the Williams & Griffin store. This is, apparently, a WW2 stirrup-pump and it includes a manufacturer’s label for ‘W. T French & Son Ltd / Mysto Works / Birmingham’.

Yesterday (22nd May), Emma was using the flotation tank to process material from our recently-completed excavation at Thaxted in Essex. During the excavation, we collected bags of soil samples so that any environmental evidence could be extracted and analysed. The environmental evidence is extracted by flotation. Our flotation tank consists of three containers and a hand-operated pump. In manual water flotation, the soil is added to water and filtered, and the process produces waste water and silt sludge, heavy fraction (like stones), and flot (small residues). Flotation is usually undertaken by an archaeo-environmental specialist, who then checks through the fraction and analyses the dried flot. Now the Trust can process our own bags of soil samples, and send just the flot to specialist Val Fryer for analysis. Environmental material includes seeds, shells and macrofossils of, for example, organic material, which contributes important evidence towards the interpretation of an archaeological site *. The flotation process is impressive, as numbers of large bags of soil samples are reduced to a few tiny bags of flot!

Emma made the flotation tank using the article ‘The hand-pump flotation system: a new method for archaeobotanical recovery’, by C. P. Shelton & C. E. White, 2010 (published in the Journal of Field Archaeology, vol. 35, no. 3).

The images show large bags of soil samples waiting to be processed behind Roman Circus House, the flotation tank and pump, Emma removing fraction from the flotation tank yesterday, one batch of the heavy fraction, and the extracted flot, in the sieve and tied up into a tiny bag.

 

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* This extract is from specialist Val Fryer’s environmental report in CAT Report 412: ‘… Excavations prior to redevelopment at the [Colchester Garrison Alienated Land sites] revealed a range of features of Neolithic to medieval/post-medieval date. These included an extensive Roman cemetery, which appears to have been in use between the 1st-4th centuries AD. Samples for the extraction of the plant macrofossil assemblages were taken from three of the excavation areas (C1, C2 and J1). Thirty two assemblages were assessed, along with the fills of four cremation urns (CAT Report 361). This assessment showed that plant macrofossils were generally scarce, and none of the assemblages studied contained sufficient material (ie 100+ specimens) for quantification. However, a group of nine samples did contain material, which was considered to be significant to the interpretation of particular aspects of site use, and these form the basis of this report. In addition, a single charred fruit, which was hand picked from the fill of pit JNF252, is also included.

Methods
The samples were processed by manual water flotation/washover, and the flots were collected in a 500 micron mesh sieve. The dried flots were sorted under a binocular microscope at magnifications up to x 16, and the plant macrofossils and other remains noted are listed [in the table]. All plant remains were charred. Nomenclature within the table follows Stace (1997) and identifications were made by comparison with modern reference specimens. Material is classified within the table as follows: cereals, herbs, tree/shrub macrofossils and other plant macrofossils. The presence of other material types is also recorded.
As quantification was not undertaken, the density of material within each assemblage is expressed in the table as follows: x = 1-10 specimens, xx = 10-100 specimens and xxx = 100+ specimens …
Although rare, cereal grains, seeds or tree/shrub macrofossils are recorded from all nine of the assemblages studied. Preservation is poor to moderate, with most of the grains being either fragmented or puffed/distorted as a result of combustion at high temperatures.
Possible barley (Hordeum sp.) grains, with noticeably convex profiles, are present as single specimens within both the bustum context (sample 68) and the pits containing pyre debris (samples 8 and 69). However, none are sufficiently well preserved to enable close identification. Wheat (Triticum sp) grains are particularly abundant within sample 8 from pit with pyre debris CF126, along with a number of indeterminate grain fragments. The wheat grains are mostly of an elongated “drop-for” shape typical of spelt (T. spelta), although occasional rounded hexaploid forms may also be present. A single, large, heavily charred fruit was hand picked from the fill of pit with pyre debris JNF252 (sample 96) …
Weed seeds are particularly rare within the current assemblages, and most are poorly preserved. A small number of legume (Fabaceae) seeds with elliptical cross sections are recorded from sample 9, from bustum context (JNF34) … Hazel (Corylus avellana) nutshell fragments are particularly common within the three Late Neolithic pit assemblages (samples 1, 2 and 40), and small fragments are also present within two of the pits containing pyre debris (samples 16 and 69).
Charcoal fragments are common or abundant within all nine assemblages. Other plant macrofossils are rare, although pieces of charred root/stem are recorded within the bustum and unurned cremation burial deposits.
Fragments of black porous or tarry material are present in all nine assemblages. Most are probable residues of the combustion of organic remains (either plant materials or possibly even body tissue) at very high temperatures, and are commonly seen within both cremation and pyre deposits. Burnt bone fragments are present or common within the unurned cremation burial, the bustum deposits and the pits containing pyre debris. Other remains are rare, but it should be noted that small coal fragments are recorded from a number of samples. However, it is considered most likely that these are modern contaminants within the contexts …’

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CAT

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