History hunters: metal-detecting technology in search of gold
Metal-detecting technology has advanced enormously from the military equipment that was used to find landmines during the Second World War. Now sophisticated devices allow detectorists to follow their sport of hunting for lost treasures.
The metal detector has a long history, one that pre-dates the x-ray vision of comic-book heroes by many decades.
It became clear to scientists in the 19th century that electro-magnetism could provide a way of locating metal objects hidden behind or beneath other materials. This ability was initially sought to help miners find ore bodies, while it was also developed to try and locate bullets in injured soldiers.
While further developments took place in the early 20th century, it wasn’t until the Second World War that metal detectors were produced in quantity.
A design originally created to locate unexploded shells was completed by Polish Lieutenant Jozef Kosacki and pressed into service by the British in the North African campaign, where it significantly accelerated British advances by clearing land mines much faster than by traditional methods.
The Polish detector weighed 14kg and operated in much the same way as basic detectors today, with two oscillators working together to generate a steady tone. When the machine’s detecting coil comes into close proximity to a change in conductivity below it, the change of induction in the coil alters the balance of one of the oscillators, causing a change in tone.
In some detectors, this would shift the tone of a note the user hears or, if the detector’s circuit is tuned to run silently, the change in ground condition results in a variable tone where before there was none.
When consumer detectors first came on the scene this was a starting point onto which other refinements were added.
Simple tuned circuits have little ability to differentiate between one metal and another and will detect mineralised materials as well as metal. If finding coal and slag was not irritating enough for the hobbyist, spotting piles of iron quickly became boring. While very skilled detectorists could differentiate some metals and objects by sound alone, when detectors were invented that could exclude iron the hobbyist market took a big leap forward in popularity.
The converse is true with commercial security detectors that in the main are tuned to spot iron rather than non-ferrous targets. While a treasure hunter’s detector will often be set to miss a lump of iron the size of a hand gun but spot a small gold coin, an airport detector will pick up a metal belt buckle but disregard a large chunk of gold on a traveller’s wrist.
An electronic oscillator has several components but for a metal detector the key is an inductor, generally a coil of wire.
If you have a stable oscillator purring away and you wave some metal close to the inductor in the circuit, the circuit’s attributes will change, and the speed of the oscillator will change along with it. This is the basic mechanism of a metal detector. The coil waved across the ground is the inductor and the rest of the machine is the oscillator and ancillary circuitry to power it and push the sound of the oscillator to the operator’s headphones.
For very basic detection, for example sensing a mine hidden an inch below earth, all that is needed to spot the object is a change in tone of the oscillator. Anyone in a minefield running the coil over a mine will hear the tone in their earphones suddenly change and will be sure that they have found a mine.
Over the years, the coils of metal detectors have changed to provide a range of signals which in turn are fed to increasingly sophisticated signal processors in the machine’s control box. With the advent of complex digital signal processing and ever more powerful microcomputers, detectors have become small portable signal-processing computers.
Early metal detectors relied on the operator to distinguish and evaluate the unfiltered signals from the machine or conversely dig every signal they got, but the modern machine gives a wealth of information about a located find before the user needs to dig it up.
The metal detector has come a long way since the heavy valve machine of World War Two. Now there are a plethora of devices with different technologies for different needs and terrains. There are underwater detectors, detectors for highly mineralised environments like gold fields, detectors for the saline conditions of wet and dry sand and detectors for normal soil conditions.
While the first detectors were large machines with primitive electronics, modern designs contain signal-processing computers that interpret the signal from the coil and interpolate information about targets such as depth, metal and ground conditions. An era of carbon-fibre bodies, Wi-Fi linked, GPS-locating, web-enabled machines is here.
Gary Blackwell of the highly regarded hobbyist website Gary’s Detecting says: “With today’s metal detector technology, the future very quickly becomes the past as performance boundaries are always being pushed. Machines like the Deus XP, made in France, have software updates like any other computer, allowing the user to stay ahead of the game. Loading a machine with technology is great – the real magic is making a machine loaded with technology that everyone can operate, no matter what skill level.”
Metal detecting is not all about finding treasure; there are so many other things to take into account, such as being out in the countryside, spending time with friends and the sheer enjoyment of a hobby.
Metal detectors are no longer called mine detectors, but while their targets have changed, their purpose of finding hidden objects remains. With the founding of the hobby of metal detecting, the initial reaction to ‘treasure hunters’ was very negative. For thousands of years people have been losing and burying items in the ground and then suddenly they could find them again and it came as a shock, especially in the world of archaeology.
Institutional fear and envy rose quickly and metal detecting was banned out of hand in many countries. It remains a serious criminal offence in them even today and still sits in a twilight world of legality in many others.
The US and UK, while suffering a backlash in the early days, nonetheless didn’t ban metal detecting, and the UK with its aeons of patrimony, has benefitted massively from its thoughtful regulation of the hobby. This enlightened standpoint has been responsible for the recovery of a large trove of history for the nation.
What has been understood and harnessed is that metal detectorists do not follow their sport for money and would quickly starve if they tried. They love their hobby because of the history they recover.
British treasure laws tacitly accept that and give detectorists a channel to hand their finds over to archaeologists for study and the nation for safe keeping while giving them a fair reward for it. As a result, a fabulous series of finds have been unearthed by metal detectorists. These are well rewarded ‘finds of a lifetime’ for a detectorist but when spread across an army of searchers combing the country at weekends, it amounts to little average reward.
What the UK has in fact developed by embracing metal detecting is a legion of amateur archaeological scouts only too pleased to turn over their finds to the UK’s network of Finds Liaison Officers.
While a find like the Galloway Hoard, which earned the finder Derek McLennan a reward of nearly £2 million, may be the equivalent of winning the National Lottery, it transpires that people are quite happy to watch others detect on YouTube rather than buy their own machine and sally forth. In the same way as game players have hugely popular YouTube channels where people watch them play rather than play games themselves, treasure hunting channels have large followings, too.
Beau Ouimette, aka Aquachigger, is a leading American YouTube treasure hunter and metal detectorist famous for his Civil War artefact finds and river searching. While the British may be fascinated by ancient Celtic, Roman or medieval finds, the huge US YouTube audience is riveted by searchers finding GoPros, Apple iPhones and Ray-Bans in rivers. Whereas an English detectorist might regard a musket ball as scrap, their US counterparts are overjoyed to find them.
“These days, for most people, the treasure is the video,” explained Ouimette. “When I find something, maybe a million people find it with me. It doesn’t matter if it’s gold or a shell fragment from the Civil War, or a button or a horseshoe, it’s the journey that’s important.” With a million subscribers watching Aquachigger you have to agree that treasure hunting has little to do with what museums call treasure and more about what people find fascinating about history and artefacts, even modern ones.
While the value may well be in the video, real treasure is definitely in the ground. With the advent of the metal detector an unprecedented number of small finds have been unearthed, and because of the laws that embrace detectorists in the UK, many spectacular ones too.
Ian Goldbart runs Sovereign Rarities Ltd, one of Britain and Europe’s leading coin dealers. He comments: “The double leopard, or double florin of Edward III, has only three known examples. The most recently discovered one was found in a field, apparently, in Kent, by a metal detectorist, in 2006. The Coenwulf Gold Penny, a unique specimen, was also found by a detectorist. Because UK laws allow for such finds, detectorists are preserving and discovering pieces of our history that might never come to light any other way. I’d be surprised if another Coenwulf penny ever turns up.”
The Coenwulf Mancus is one of only eight gold coin types produced in Britain between 796-821 AD and is the only specimen of its type. It is now in the British Museum. It was found in the mud of a footpath in Biggleswade, a solitary coin find in a location only a metal detectorist would search.
Likewise, the gigantic Grouville hoard was found in Jersey by two detectorists after a 20-year search. Having discovered a lone Celtic coin in a field, they kept up their search over the years until the day they bought a deep-seeking detector that could detect to a depth that found the hoard of 70,000 Iron Age and Roman coins and jewellery weighing in at 750kg.
For every artefact or hoard held in a context where archaeology might find them, many more are strewn at random across the country: in wood, on hill and under farmland – where they are at risk from modern farming practices, as ploughing shatters and fertiliser dissolves. Fortunately, detectorists are recovering some of this heritage.
Metal detectors have kept pace with technology, and the next wave are likely to include primitive imaging. There are already magnetometers that make crude underground images, but these devices are bulky and do not discriminate for the non-magnetic targets metal detectorists seek. However, it seems it is only a matter of time before detectors will show clear images of what is roughly below the ground, with machines already showing depth, an approximation of size of target and metal type on their digital readouts.
The holy grail for treasure hunters is a detector that can detect at distance. While that technology is nowhere to be seen, it hasn’t stopped companies producing and selling such devices to optimistic customers. Seeing metal objects under a foot of earth seems pretty magical, so divining them from afar isn’t such a stretch for the hopeful imagination. Sadly, though, no such device has retained any credibility.
That doesn’t stop detectorists hunting treasure from afar. The canniest have been using Google maps for years and are now turning their attention to lidar maps of Great Britain to try and glimpse the sort of lumps and bumps in terrain that might give away long-lost sites. It is nothing new for metal detectorists to fly drones across fields on the lookout for clues to new finds.
Treasure will always have an allure, and while finding hoards of ancient coins will remain for most just a dream, metal detectors are a way of touching and recovering history against a backdrop of an environment where objects are constantly lost or degraded through changes in land use and farming practice. Where once the manual activities of ploughing, building or road-making uncovered the past, modern equipment obliviously chews through it.
It is fortunate that there is an army of lone detectorists trudging up and down ploughed fields prepared to find sacks of aluminium and other such pieces of trash incidentals in the hope of discovering a find of a lifetime. As now and again they do.
1715 Treasure Fleet
Metal detecting is not just about dry land. The 1715 Treasure Fleet returning with the yearly revenue from Spain’s South American dominions was sunk en masse by a hurricane off Florida. Eleven of 12 ships that were sunk contained the modern equivalent of billions of dollars in silver, much of which still lies under the beaches of Vero Beach in Florida. Enough still remains for specialist boats to dredge for treasure when conditions allow. After removing 3-6m of overbearing sand, divers descend with metal detectors in the search for pieces of eight and other such artefacts. In 2015, treasure hunter Captain Jonah Martinez and his divers William Bartlett and Dan Beckingham recovered 350 coins worth $4.5m including extremely rare examples of ‘royal’ gold 8-escudos.
After 20 years of looking, Reg Mead and Richard Miles finally discovered one of the greatest ancient hordes of all time on the Channel Island of Jersey. The Celtic hoard, interpreted as a tribal stash against the invading Roman legions of Julius Caesar, was a 750kg lump of fused silver and gold coins with jewellery sprinkled inside it. The 70,000 mainly Celtic silver staters are valued at between £7m and £14m; the value of each item diminished by the sheer number of examples. Dismantling and documentation of the hoard coin by coin has taken years.
The Hand of Faith
Metal detecting is not all about priceless ancient artefacts. In Africa, Australia and America the activity is often aimed at finding raw gold. A giant example of this was the discovery of an 876-ounce (27.25kg) nugget called the ‘Hand of Faith’. It was found in gold country in Victoria, Australia in 1980 and put on display in Las Vegas’s Golden Nugget Casino.
The ‘Staffordshire Hoard’ found by Terry Herbert in 2009 near Hammerwich, Staffordshire, contained 3500 items, many of which were gold or silver. In gross terms, the exquisite Anglo-Saxon pieces weighed in at 5kg of gold and 1.4kg of silver. They where considered initially to be battlefield loot in an era when high-status individuals would adorn their weapons and armour in gold and precious gems. There are now other interpretations.
Many homes have a piggy bank, a jar of coins or a suitcase with heirlooms. Coupling this hoarding instinct with war and the fall of an empire results in hoards both large and small left forgotten in the ground. The Hoxne Hoard was found in a Suffolk field in 1992 by Eric Lawes, who was looking for his farmer friend’s hammer. Lawes uncovered silver cutlery and gold jewellery, sparking an urgent excavation that uncovered the largest trove of late Roman gold and silver coins found in Europe.