From 1976, hobby metal detectors became available on the Dutch market. At that time, the focus of detector manufacturers was entirely on performance, while ease of use and comfort were neglected. After a hesitant start, the number of users steadily grew, making metal detecting a popular hobby. Users quickly demonstrated that they could still recover many metal finds from sites after the completion of archaeological excavations. In and around the filled-in pits and leveled mounds, remarkable objects still surfaced. This initially caused some resistance among archaeologists to the phenomenon of ‘metal detecting’. Especially when some individuals started digging in excavation pits, the opinion of many archaeologists about the users and metal detectors quickly turned negative. In professional archaeology, metal detectors only started being used regularly in the 1990s. In the meantime, the detector had also evolved in terms of technology and ergonomics. Decades later, the metal detector is fully accepted as an essential tool in the archaeologist’s toolkit. This is demonstrated, among other things, by the KNA Metal Guideline1 (2021), which provides detailed information on metal detection. The appendix of this guideline includes additional explanations on the operation of a detector, the desired detection equipment for professional research, and field applications. ‘ Metal detecting requires a clear mind’

Since the 1990s, the analog detector brands C-Scope and Tesoro have been the most popular among excavation institutions. Especially the Tesoro was known as a simple to operate, solid, and reliable device. However, these devices have long exceeded their expiration date and are slowly ‘dying out’. Even the manufacturer of Tesoro has gone bankrupt. This sometimes gives a sad sight of a once glorious metal detector standing in deplorable condition against the wall of an excavation pit, rusting away. Therefore, archaeological excavation institutions must switch to digital metal detectors.

This article delves deeper into the use of the digital detector in archaeology. A choice is made for a suitable brand and type of metal detector for archaeology. The various useful detector programs for archaeological purposes are discussed. In the final part, an overview is given of the easy and difficult-to-find archaeological metal objects and the associated pitfalls. The article concludes with suggestions for the user regarding the maintenance and daily use of the digital detector.

INCREASE IN METAL FINDS

Metal objects usually have different functions and forms than (for example) pottery or bone and are often well datable. The use of metal detectors has increased the datability of the site and has highlighted more and different aspects of the past than before. The introduction of metal detectors has led to a significant increase in metal finds in archaeological research, especially in the form of small finds such as coins, pins, buttons, nails, and buckles. Due to the establishment of PAN – an initiative of VU Amsterdam – detectorists have registered around 150,000 finds.

The detector can be used in archaeology in the following ways:

• From ground level before the excavation begins
• At various levels during excavation with a machine;
• During manual deepening;
• On spoil heaps and in soil from features
• After filling in the excavation pits
• To locate finds in large remote areas such as Roman marching camps.

In current practice, the step ‘after filling in the excavation pits’ is often not carried out. For the best informational value of the excavation research, it is important to do so, as there are several examples where, after completion of the research, detectorists have found significant finds.

FAREWELL TO THE ANALOG METALDETECTOR IN ARCHAEOLOGY, BUT WHAT NOW?

The ‘extinction’ of the older analog devices is a fact. This means that excavation institutions must switch to new digital detectors. And that brings some questions. It is no longer just a matter of placing new batteries once a month, turning a few knobs, and running with the detector. The digital detectors require a different way of handling them. They use more power, receive updates, and the number of different setting options is impressive. Detector manufacturers aim to serve all their customers with options for different needs depending on what the user wants to find: Australian nuggets, thin European silver coins, or thick American silver dollars? It should all be possible with modern detectors, and it is. Most modern detectors have several standard programs so that even beginners in any part of the world can pick up the detector and search successfully according to their needs and circumstances. However, these standard settings do not </span > include the appropriate settings for use in archaeology. These will need to be set in the optional programs.

Which Digital Metal Detector?

Poor detectors are no longer made, apart from Chinese toys. The well-known top brands Nokta, Minelab and XP are almost equal in terms of performance. However, not all models of these brands are suitable for archaeology. The KNA guideline states that: ‘for use during archaeological excavations, a quality entry-level model is usually sufficient’. However, the current entry-level models often have a fixed and too large search coil for optimal use in archaeology. They also lack the necessary customizable program options for use in archaeology. Moreover, they are not all waterproof.

Which modern detector is suitable for archaeology? The Deus II from XP has proven to be a good choice. Why? • Ergonomically, the Deus II is ultralight, no more staff absences due to overloaded joints. • The headphones are not fully enclosed. This allows good contact with the surroundings (colleagues – excavator ) to be maintained. • Waterproof, no more hassle with plastic bags as with analog detectors. • Wireless, both the coil, the electronic box, and the headphones. Therefore, the shaft with coil can be easily placed further away without being connected to wires that always get caught somewhere. • The detector can be set with 10 standard programs and 10 optional, customizable programs. The 10 optional programs are particularly useful for archaeology. • Easy to charge, built-in batteries that have enough charge for more than a day of searching. • Sturdy and reliable. The warranty is 5 years with quick repair service. • Works with separate modules, such as the separate coil, electronic box, and headphones. The separate modules are easy and quick to repair and/or replace. • Several archaeologists with their own detector have already chosen this XP Deus. The ease of use without wires and the ergonomics of the Deus II are a plus. The electronic box can be carried separately in a pocket. Then only the shaft and coil are held. One can therefore search comfortably all day with little strain on the arm/shoulder. The recommended size of the search coil for archaeology is approximately 22 cm (9 inches). Only in very large find locations with very few signals is a 27 cm coil somewhat more useful because it covers more ground per sweep. A larger coil allows you to cover ground faster, but it is heavier.

Depth Range of Metal Detectors

For hobbyists, depth range is sacred. However, the depth range is much less important in archaeology. All top models must reduce their sensitivity when used in archaeology! Due to the method of excavating in layers during an archaeological excavation, a large depth range is often not desirable, as this can disturb the relationship between find and context. Typically, the layer is deepened by about 5 cm at a time with the excavator. A detector set with a too large depth range can detect finds very deep. When excavating in the deep pit, it is not always possible to determine in which habitation layer the find lies. The big advantage of reducing sensitivity is that the detector operates more stably with fewer interference signals and discriminates more accurately.

SEARCH PROGRAMS

The search programs must be set on the detector. The settings for the different archaeological programs can be found in the attached diagram. The following search programs are suitable for use in archaeology:

• Program A for the Iron Age and Bronze Age. This program has the lowest discrimination, making it possible to detect not only iron but also Iron and Bronze Age pottery fragments. These fragments contain metal. This can also serve as a warning for the presence of larger fragments (pots) of this fragile pottery.
• Program B for medieval and Roman outlying areas + spoil heaps. This program sets discrimination so that micro-iron and rust particles are almost ignored. Pottery is also ignored. Also suitable for finding small coins such as minimissimi, sceattas, and thin medieval silver pennies.3
• Program C for medieval and Roman habitation layers and settlements + spoil heaps. Due to the amount of iron, these are places where the discrimination ability of a detector is heavily tested. More or less complete iron nails and other not too large iron objects are not completely discriminated in this program but are indicated with a soft low tone.
• Program D for the top layer before and after the excavation. In this program, iron and coke are ignored.
• Program E for locating finds in large remote areas such as Roman marching camps. In this program, the detector is set to full power for maximum depth range with some discrimination of micro-iron and rust particles.

CHOOSE AND GO

In practice, one selects the appropriate program A, B, C, D, or E for the excavation type. The detector remembers the last set program, so during the entire research, it is only a matter of turning the detector on and off. The Deus II detector has many setting options. In the attached diagram, the most important settings are listed for the respective excavation type.

With advancing insight in general and personal experiences these values can be adjusted. While searching, settings can of course be adjusted to the search conditions on-site. However, if these changing settings are not saved in the program, they will be lost when the detector is turned off. NB 2: It goes too far to delve deeper into all the settings in this article. For that, study the detector manual and watch the Metal detecting Skill School videos on YouTube.4

VDI

The term ‘VDI’ stands for ‘Visual Discrimination Indication’. This is - in addition to hearing a tone in the headphones - the number that is clearly visible on the display of a metal detector when a metal object is located under the coil. This number can provide extra information about the object in the ground. Depending on the position of the object relative to the coil, the numbers can vary. The highest and lowest VDI number of an object is indicated in the table. The height of the numbers depends on: - the material: bronze and silver have a higher VDI than gold; - the shape: a closed ring gives a much better signal than an open ring; - the mass of an object: the more mass, the higher the VDI; - the position of the object in the ground.

Due to current low-frequency detectors, it is likely that this type of thin Roman fibula with an iron core in the broad spring roll (no. 5) is now almost never found. This also applies to this small Roman iron ring (no.6) with bronze plate with a VDI of 7.

WHEN IN DOUBT, ALWAYS DIG!

In the diagram, there is a tipping point around the lead weights (VDI 46-48). Above that are the objects with a higher VDI that most searchers will still find. For objects with a lower VDI, it is likely that they will be missed first when searching hastily and carelessly. The most difficult objects to find are spiral shapes, small, thin, composed of different metals, or have a combination of these factors.

The Deus II is a detector that provides very good information about an object through sound, the tone. The VDI numbers on the display are just an aid. The numbers usually correspond with the tone, but sometimes not. The golden rule is therefore: when in doubt, always dig!

STEPS FOR HANDLING INTERFERENCE (EMI)

Nearby high-voltage pylons, electric motors, generators, buildings, and urban areas can cause EMI (Electromagnetic Interference) in the detector. This results in loud, irritating hums and crackles in the headphones. Modern Multi-frequency machines (such as the Deus II) are more sensitive to this because they transmit and receive on multiple frequencies simultaneously. To tackle this problem, follow these steps: 1. Hold down the top right button on the electronic box of the Deus II for a few seconds. The detector will automatically scan several </ span> frequencies close to each other and will select the frequency with the least EMI. 2. If necessary, reduce the sensitivity from 95 to, for example, 85.

If there is still too much EMI:

1. Select program number 7 on the Deus II: MONO. This program works just like the Deus I with a single main frequency. Use the plus and minus buttons to find the best main frequency with the least EMI.
2. Then use the scan function again.
3. If necessary, further reduce the sensitivity to about 85.

QUALIFIED PERSONS FOR DETECTOR USE

‘Good searching’ means, first and foremost, that it is done by qualified persons, because not everyone has the right search technique and can properly set the detector for the excavation! The detector and associated accessories must also be maintained. Therefore, it is important that a designated person is responsible for the metal detector(s). This includes regularly charging the batteries, cleaning, checking, and installing available updates. Nearly all archaeologists have their own trowel and spade they are used to and trust. Likewise, more archaeologists have their own detector. This ensures that the detector is charged and the settings are correct. They know the peculiarities/signals of their own detector inside out and can therefore use the tool optimally.

METAL DETECTING REQUIRES A CLEAR MIND

Finally, once properly set, searching with the right digital metal detector is fairly straightforward. Now it comes down to good search technique. Unfortunately, it has been shown that there are not many searchers with the correct search technique. This is evident everywhere, with people wasting their precious energy by swinging the search coil too high, whether during a detector day of an association or company, or in archaeological excavation pits. This is despite the fact that every metal detector manual extensively explains the correct search technique in words and pictures. Developing good search technique requires intention and practice! Those who search attentively with good technique are not concerned with making meters, completing sections or meeting the deadline of the excavation. Good searching – with any perfectly set expensive detector – requires a mental attitude of ‘being in the here-and-now’, and that requires a clear mind. Those who feel rushed will quickly adopt a less effective search technique, leading to a decrease in the total number of finds, particularly an under-representation of smaller and lighter objects.