Note 4: What next? Assessment.
What have you found?
Composition: modern metal detectors can give some indication of what metal you have located, but if you pick up objects field walking you may have to rely on traditional methods of identification:
- Gold is usually recognisably yellow and in good condition. For example the gold dagger hilt shown below:
- Silver can be bright shiny metal, tarnished (black), or covered in bumpy purple-grey corrosion. The image below shows corrosion on medieval silver coins.
- Green corrosion indicates some copper content. But beware: when silver or gold are present, the copper corrodes first and the silver or gold will be covered in green corrosion. The example on the left below demonstrates the distinctive green patination. The example on the right shows a conserved example.
- Brown lumps with a heavy covering of soil: try a magnet, iron usually responds to it. A typical concreted iron example is shown below:
- Watch out for additional materials, such as inlays or plating, they can be fragile. Handle with care.
- Watch out for attached organic remains' like bone, antler or ivory handles, leather straps, wood remains, or textiles. These may be stained green or brown from corrosion.
- Look under a magnifying lens or microscope to see more. You might want to keep a record of what you see, describing the soil type and what the corrosion looks like.
You can talk to experienced detectorists and look at reference books to learn more about your finds; speak to your FLO, they can help to identify what you have found.
Does it need treatment?
Active corrosion: if you see these signs, store your find in a dry box. This should be enough to prevent further corrosion. Most finds need no active treatment, but if problems still persist, consult your FLO who can put you in touch with a conservator.
- Iron corrodes most easily. Active corrosion is indicated by bright orange powdery crystals or little droplets of weeping' iron. This corrosion will carry on, causing the find to split into many fragments unless it is kept dry at less than 15%RH. The image below demonstrates an example of active corrosion.
- Copper alloy: Active corrosion is pale green and powdery. Store the find dry. Consult a conservator if the corrosion continues or the find is fragile, it may need chemical stabilisation and consolidation: these are jobs for the professional!
But it's covered in soil and corrosion shouldn't I wash it?
Do not clean Treasure finds (The Treasure Act 1996 Code of Practice advises finders that they should not clean finds, as this might damage archaeological evidence and may reduce the award paid). Conservators will ask you not to wash most archaeological finds; this is because it can cause harm by introducing moisture, causing further corrosion, and damaging fragile remains such as loose metal plating, inlays, and associated textiles or organic material.
Surrounding soil can contain evidence of the burial environment. However, many metal-detected finds are from disturbed ground such as plough soil and have only survived because they are quite robust. Often finds are fairly modern, some are collectibles like buttons and badges, and others are agricultural, like horseshoes. In these cases careful washing can be carried out. Rinse the find gently in a plastic bowl of clean water to avoid losing small fragments; if necessary use a soft brush to remove the soil.
Avoid leaving the finds to soak. Wash each find individually. Change the water if it gets cloudy. TAKE CARE be alert to any fragile remains. Leave the finds to dry at room temperature (sudden heat can cause cracking) and pack them in your dry box as soon as possible, to prevent corrosion.
What about X-rays?
Occasionally radiography may be recommended by your FLO when the detail on a find is obscured by corrosion. X-raying is used routinely to reveal valuable information from archaeological iron finds, but is also very helpful for copper alloy and other metal objects, especially coins. Details of decoration and construction can often be seen, and weak areas are shown without the need for cleaning. FLOs can arrange radiography for you but there may be a charge for this service.
What should I do?
Consult your FLO and Report Finds Take Advice Before Cleaning. Stabilising metals: Dry storage is usually sufficient. Remember incorrect cleaning and treatment can reduce the value of your find, seriously damage, or even destroy it.
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