Flotation tank blues

Updated: Sep 30, 2018

Deep down in every archaeologist there lurks an Indiana Jones fighting to get out: no matter how many times we all dutifully explain during public site tours that we don't dig to find artefacts, they are in fact only a means to an end for the important role they play in site interpretation, we're all lying - everyone wants that thrill of getting the star find of the day, hence the mad rush of everyone on site towards someone who's just gone 'hey - look what I've got here'. Much of excavation is deeply tedious, painstaking work that has to be done - photo cleaning springs to mind here - but at least on-site you have the camaraderie of the rest of the team to keep you going.

This is not the case for the post-excavation work, which tends to be a fairly solitary experience. Take for example the processing of environmental samples, commonly known as 'flotting'. Environmental sampling is another of those arcane archaeological arts that's vitally important to any excavation, as the end result is the retrieval of carbonised material - such as cereal grains - which you need to get good radiocarbon dates, but is decidedly unglamorous. You start by getting the special blue sample bucket and lining it with a special (also blue) plastic bag, a clean hand shovel and clean trowel, then carefully filling lots of these plastic bags with soil from the particular bit you're excavating, all of which are dutifully recorded, double bagged, tagged, labelled, entered in a record sheet and in a record book, fingerprinted - OK I made the last one up but you get the idea - archaeologists understand the necessity for chains of evidence just as much as the constabulary!


Environmental sampling in progress - blue bag in a blue bucket

After that, which is time consuming and annoying in itself, the average digger forgets all about them (apart from occasionally swearing when they trip over the mounting piles of sample bags outside the finds hut) - since they are now the preserve of specialists - i.e. the environmental archaeologist. Actually you don't have to be an environmental archaeologist to process samples, just have a penchant for spending your days up to the elbows in cold water and mud, with occasional breaks fro cups of tea, since 'processing' means putting bits of the sample in water, shwooshing it about and breaking up all the little bits till it's reduced to silt and catching all the interesting stuff that floats off:


Flotting is pretty tedious work - even the dogs are bored

In the pic above the sample bags are in the barrow, the tank has a mesh clipped to the edge of it to put the sample in, and the handsome dudes are Bran and Patch. The other one is Dave, who is a specialist, but an osteoarchaeologist moonlighting as an environmentalist. Actually he volunteered to help out - we couldn't process the samples in Rousay as it's been so dry this summer than everyone's boreholes were drying up and we couldn't get any water - running water in fairly large quantities being necessary to wash through the samples. Rubber gloves are vital for this job, if you want to have any fingers left at the end of it. Your hands are still freezing though as you have to have gloves thin enough to feel what you're doing and they don't keep out the cold. The idea is to gently break up all the clumps of soil - ok if it's light but a different proposition when it's all claggy & clay.


For hands that do dishes!

And this is what it's all about - collecting in a fine mesh sieve all the flot - i.e. the stuff that floats off when you break up the claggy mess in the cold water, all the important carbonised material that can both be analysed by the real environmental specialist to give you important information about agricultural practices and much else, and also be used for radiocarbon dates:


Sieve collecting the flot

The flot then gets lovingly wrapped in muslin, and hung up to dry along with its label, on a clothesline if it's dry, or indoors if not - this is where having a stove with a clothes dryer above it really comes into its own (please ignore the obviously unfinished bit of roof lining in the background - that's one of those little jobs I've been meaning to get around to since 2013 but always find much more important things to do - this is a warts & all dig diary after all):


Washing & flot in perfect harmony

You are then left with the flot grot - or to be technically correct the residue or heavy fraction - all the stones and bits and pieces that neither dissolve and nor float, but which includes fragments of bone, pot, slag etc that went in with the sample (which was necessarily was collected in large chunks so a not to damage the carbonised remains). This is carefully dried in trays - luckily here at Swandro HQ we have a large GP shed (general purpose - covers a multitude of sins) suitable for air drying all the grot.


Flot grot aka residue

It's dried for a reason, which is so that you can carefully pick through it using a magnet (for the hammerscale) and tweezers for all the little bits of interesting stuff - here we have some very nice fragments of copper alloy from our smithy from one of the residues:


Bits of copper alloy from our smithy

I think that qualifies as a pretty exciting find, although I probably do need to get out more, and it's not up to Hollywood standards, I can't imagine 'Indiana Jones and the Copper Alloy Fragments' is going to be a big box office hit any time soon!


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Swandro - Orkney Coastal Archaeology Trust 

Scottish Charitable Incorporated Organisation No: SC047002 

Patron: His Royal Highness The Prince Charles, the Duke of Rothesay

Registered office: Bayview Birsay Orkney KW17 2LR   email: info@swandro.co.uk