News Item: Guide to metal detecting
(Category: Other news)
Posted by support
Wednesday 18 November 2009 - 22:16:45

Like archaeology, metal detecting can be an interesting and exciting hobby.

Thousands of people own metal detectors which are useful tools for locating both metals and minerals
underground.Metal detectors are available in a number of models made by different
manufacturers, with the general rule being, the more money you spend the better and more
versatile detector you can buy. Detectors can be used to identify different types of metal and
some designs allow you to discriminate so that you are only alerted when certain metal
types are detected; this stops the inevitable bleep whenever a soft drinks can is found. The
most expensive units also give an indication of how deep a find may be in the ground.
Apart from hobbyists and airport security, metal detectors are also used by archaeologists
to highlight areas of interest before systematic excavation begins, and the responsible use
of this versatile tool can be a real benefit during an investigation.

How it works
Most detectors follow a similar design. A search loop, or antenna, is held at the end of a
handle and is connected to a control box, which contains all of the gadgetry. Most
incorporate a counterbalance which cups the forearm to aid a smooth sweeping operation.
Some detector control boxes have an in-built speaker to alert the user to a signal, but most
operators prefer to use headphones.
Detectors can use three systems for targeting metals. Pulse Induction (PI), Very Low
Frequency (VLF) and Beat Frequency Oscillation (BFO) to search up to 30cm (12 inches)
below the ground.
PI detectors send pulses of electromagnetic field into the ground. If the field makes contact
with a metal object the object produces its own field with its own frequency which upsets
the expected pattern of pulses the machine is emitting. This change is detected and the
machine alerts the user.
VLF detectors produce an electromagnetic field which is directed into the ground. Again, if
the field makes contact with a metal object the object produces its own field with its own
frequency. This new field is detected by a receiver which is incorporated into the equipment.
By tuning out certain frequencies from the receiver, different metals can be discriminated
BFO detectors are the most basic and cheap designs which interpret their signals as radio
waves. Once a metal object interferes with the detectors electromagnetic field the radio
waves become agitated and emit a tone to alert the operator.

The detecting debate
There has been a long running debate between hobbyists and archaeologists about the use
of metal detectors. The main concerns from archaeologists are about treasure hunting and
the temptation to remove artefacts from their resting place, while not recording their
provenance, combined with the loss of archaeological value in an artefact when it is taken
out of context. The detectorist's view is one of equal access and ownership of our past and
the right to freely detect given all the correct permissions. The bottom line for both sides is
one of respect and responsibility; for the historical environment, the law, and the future of
our archaeological resource.

Responsible detecting
The first step towards responsible detecting is to follow the law. You can't detect on any land
that you don't own without the permission of the landowner. You also can't detect on any
protected sites, such as Scheduled Ancient Monuments or local authority protected sites,
without specialist permission. The best way to get started is to join a local club or society,
which often issue a code of practice to their members and have lots of experience on hand
for you to call on for advice and guidance on safe places to detect.
The next step is to work in a responsible manner. Think about the implications of your
detecting. You should steer clear of protected sites and also be aware that sensitive
undiscovered archaeology could be below the surface at any time. To be on the safe side you
should aim to detect within topsoil, or plough soil, and no deeper. Work in a methodical way
and always carry a note book and finds bags so that you can record where finds are
discovered and package them properly. Ideally a hand held GPS system, or good oldfashioned,
large-scale map and compass should be used, to record the grid references of find
Finds should be treated carefully and with respect. Rubbing finds on your jeans in the field,
or resorting to 'old wives tale' cleaning remedies back home can cause untold damage. The
best way to conserve and protect your finds is to get yourself an education in conservation
first. The most innocent attempt to polish a coin can ruin it, so make sure you know what
you're doing first. Richard Hobbs has written a "Guide to Conservation for Metal Detectorist's",
which is both thorough and informative, published by Tempus Books. Your local museum
curatorial officer, or a Portable Antiquities Scheme officer (see below), can also advise you
about caring for finds.
Finally, you need to think about the cultural value of your discoveries. A Roman brooch may
look nice on the mantelpiece, but the same arguments of access to our past which allow
metal detecting as a legitimate hobby also apply to artefacts too. If an item is held in a
private collection and unknown to the public a piece of cultural heritage is lost. Access to
information is the key and letting your local museum see your finds allows them to be
recorded for the archaeological record. Contrary to popular belief museums can't
automatically take your finds away from you. They would just like to see them and they
may be able to provide you with some useful information about what they are.

The portable antiquities scheme
The Portable Antiquities Scheme was established in 1997 to record finds held privately for
the general archaeological record and to raise awareness of archaeology and the cultural
value of artefacts. Well over 100,000 artefacts have been recorded by the scheme in the last
seven years. Regional Finds Liaison Officers cover the whole of England and Wales offering
advice on conservation, identification services and opportunities to record your artefacts.

The treasure act
The Treasure Act of 1996 replaced the common law of treasure trove in England, Wales and
Northern Ireland (Scotland has different laws, see below). The Treasure Act removed the
need to establish that objects were deliberately hidden with the intention of being recovered,
which was one of the tests of the common law of treasure trove. The Treasure Act sets out
the precious metal content required for a find to qualify as treasure; and it extends the
definition of treasure to include other objects found in archaeological association with finds
of treasure.

What is treasure?
Treasure, according to the Treasure Act, is any object at least 300 years old when found
• is not a coin but has metallic content of which 10 percent by weight is precious metal.
• is one of at least two coins in the same find area of which 10 percent by weight is precious
• is one of at least ten coins in the same find area.
does not fall within the specific categories given above but would have qualified as treasure
trove. This object has to be made substantially of gold or silver; has to have been buried with
the intention of recovery and its owner or his/her heirs cannot be traced.
Scottish law
The law is different in Scotland. All archaeological finds in Scotland, whether of precious
metal or not, automatically belong to the Crown and are effectively treasure trove until
proven otherwise. The Archaeology Department of the National Museum of Scotland
provides the Secretariat for the Treasure Trove Advisory Panel, which deals with individual
cases and provides information and advice on the law as it relates to the discovery of
artefacts. The Crown does not always exercise its claim, but all objects found should be
reported to your local museum. After examination finds not required for the museum
collections are returned to the finder.

This news item is from METALDETECTING PORTAL
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