Visual Display Indicators (VDI), sometimes called Target IDs, are the numerical readings modern metal detectors use to classify a buried target before excavation. These numbers represent the detector’s analysis of the object’s electromagnetic properties, primarily its conductivity and ferrous content. The VDI scale provides a quick assessment of the metal the search coil is passing over. While different manufacturers use unique scales (such as 0-99 or -95 to +95), the underlying principle of assigning a number based on the target’s response remains the same. This allows the detectorist to make an informed decision on whether to dig the target or use discrimination settings to ignore it.
The VDI Range for Gold
Gold is a metal of moderate conductivity, occupying a wide range on the VDI scale depending on the item’s physical characteristics. Small gold nuggets, thin chains, and delicate earrings are low-conductive targets due to their minimal mass. These items typically register at the very low end of the non-ferrous scale, often overlapping with aluminum foil, small pieces of iron, and nickels. On a common 0-99 scale, this low-end gold frequently falls between 8 and 36, a challenging range that requires digging significant amounts of trash targets.
As the size and mass of the gold item increase, such as with heavy rings or gold coins, the conductivity signature strengthens, causing the VDI number to rise. These larger pieces of gold register in the mid-range, often between 40 and 75, a zone shared by pull tabs and bottle caps. Gold rarely reaches the high VDI numbers above 85, which are reserved for highly conductive, thick metals like copper pennies or large silver coins. The purity of the gold also influences the reading; lower-karat gold (e.g., 10K) tends to read lower than purer gold (e.g., 22K) of the same size.
Factors Affecting Gold’s Target ID
The VDI number is not a static property of the metal but a measurement influenced by several environmental and physical variables. The depth of the target is significant, as a deep item produces a weaker signal that often results in a VDI reading substantially lower than if the item were shallow. For instance, a medium-sized ring reading 50 near the surface might drop to 30 or less when buried six inches deep.
Ground mineralization, the concentration of iron oxides and conductive salts in the soil, also distorts the target’s signature. Highly mineralized soils create a strong electromagnetic response in the ground itself, which can mask the signal from a gold object or pull its VDI number downward. This effect can be so pronounced that a non-ferrous gold target may even be pushed into the ferrous range on the display. Furthermore, the detector’s operating frequency impacts the reading; a lower frequency used on the same target will yield a lower numerical value.
Separating Gold from Look-Alike Trash
The primary challenge in finding gold is that its VDI range is densely populated by common metal debris, which detectorists refer to as “look-alike trash.” The most notorious culprits are aluminum can slaw, foil remnants, pull tabs, and bottle caps, all of which share the moderate to low conductivity signature of gold jewelry. To navigate this overlap, experienced users rely on techniques that analyze the quality and consistency of the detected signal rather than just the numerical reading.
One technique involves analyzing the audio tone quality produced by the target. Gold tends to generate a smooth, clean, and repeatable audio “ping” because of its solid, non-corroded nature. Conversely, irregular pieces of aluminum or rusted iron often produce a choppy, broken, or scratchy sound as the coil passes over them. Another method is the signal consistency check, often called the “wiggle test,” where the detectorist sweeps the coil over the target from multiple angles. A valuable gold target typically yields a stable VDI number with minimal variation, whereas irregularly shaped trash frequently causes the number to jump erratically across the scale.