Friday, 29 June 2012

Detecting Under the Microscope: How Green Was my Metal Detector?

If you look on UK metal detecting forums at the moment you might be forgiven for thinking they'd all gone from being resource depleters to "eco-crusaders". they are up in arms about "green waste". They want compost banned in British farming, and can think up all manner of arguments why. There's videos on You Tube showing shock-horror pictures of fertilised landfill with plastic and other rubbish in it, a petition with 800 signatures ("Ban 'Green' Waste being dumped on the Countryside"), a campaign of letter writing to MP’s, attempts to contact the media, the NCMD getting involved. There is a teckie Campaign blog here:

So what's all this about then? Pretty simple really. At the moment, even on the best discriminating metal detectors it is difficult for most users to distinguish between auminium and the signals from certain other non-ferrous metals, so if they get a signal, they cannot tell if it is worth stooping to dig it from the sound or signal alone. So they end up digging up a lot of aluminium pieces.

Now time was when (just after Nigel Swift set the Heritage Action Artefact Erosion Counter ticking away) tekkies kept moaning that they were misrepresented. Ignoring the fact that the blurb to the artefact erosion counter said clearly it was modelling the removal of PAS-recordable objects, dullard tekkies claimed it was "number of metal objects found", adding that "but many of the metal objects we find are modern rubbish, those idjits in HA don't know this, so there!". They even did a survey to show how many modern metal objects they found an hour - trouble was when they put the results up on their forums, embarrassingly for them, it turned out to coincide precisely with what HA were saying - so they took it down).

The problem is now reality is in some areas coming to match the propaganda. There is a lot of extraneous matter in green waste. Some householders are not so fussy about what they throw into the green waste bins when segregating rubbish. A bigger problem is collection of organic waste in parks and road sweeping. In amongst the fallen leaves are all sorts of other stuff. Theoretically this is screened out at the processing plants, but obviously what the tekkies are finding in the fields shows this screening is less than effective. Aluminium is not magnetic, so has to be sorted out by hand.

The result of poor sorting means that shredded aluminium is getting into the fields. And its causing problems for those hobbyists who want to use an electronic tool to hoover those fields for archaeological collectibles. The aluminium is slowing down the searching sites by producing too many signals. Hence the campaign.

A comment that encapsulates the issue and deserves immortalising as the spirit of the campaign:
I have lost a Romano British temple/shrine to it…
What that means is at least one Roman temple will not be so heavily looted of its archaeological content as the rest as a result of 'green' farming methods using poorly sorted compost.

The reason why metal detectorists in the past few weeks have become interested in (even militant about) this issue is because people are now noticing they are losing searchable fields, rather than because they’re suddenly growing a conscience about fragile resources. If they were so interested in countryside conservation, why were they silent when this problem first became prominent some five or six years ago? This is not a problem just in the UK (Deborah K. Rich, 'Taking out the trash: Municipal green waste needs cleaning up', The Chronicle  November 7, 2007). It surely is in improving methods used to screen waste that the answer lies. Why are metal detectorists calling to "ban" it for selfish reasons when the problem should be addressed by improving screening? I think the problem is the simplified black-and-white world many of them seem to live in.

For a rather less extreme response to the problem:  'Contamination of green waste can result in non-collection or the waste going to landfill' St Albans council News release: 18 October 2011.

Vignette: From 'Eco-warrior Chick'

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