Attention should be drawn to a very important distinction, which is between what an archaeologist would consider as archaeological evidence if found on (or off) an archaeological site, and what is considered collectable by the antiquity collector. A quick comparison between the "antiquities" sold online (eg through eBay or an antiquity seller's online gallery) and the finds section of any modern excavation report will quickly reveal that what is sold as collectors' pieces are a very narrow selection of the whole artefact assemblage from any site, assemblage or culture. The antiquity collection is therefore the product of negative selection.
But of course a metal detector "bleeps" (many of them actually make an annoying whining noise) when a piece of metal is "detected". That's what they are for. While detectors now can "discriminate" targets (ie the searcher chooses to filter out certain metals, like iron which most collectors do not appreciate in their collections and aluminium, or concentrate on items which give coin-like signals) still many detected items are not deemed worthy of adding to the collection at home. Some of these items may be sold on (Roman grots, certain broken artefacts of intriguing shape) others will be discarded on or off site. Increasingly now the unwanted pieces of artefacts of non-ferrous metal are sold off as scrap metal. In other words, a large number of pieces of what an archaeologist would consider to be archaeological evidence are hoiked out of the ground and after a cursory look, are thrown into the scrap bucket and end up being melted down.
A thread on "detecting Wales" ( Off to the rubbish yard tomorrow - guess the cash amount?) illustrates the process. The list member shows a photo of a bucket full of corroded metal scraps, rather like (but less full than) the one in my photograph and asks fellow detectorists to guess how much money he will get for it as scrap. The actual amount for three bucketloads was £58 cash.
It seems that its not only the items which are unrecognisable to the untrained eye or uncollectable that are thrown away by collectors. In a another scrap metal bucket thread
on the "Detecting Wales" forum (Senior Member romano-brit , August 22, 2011)warns rally organizers that they might want to check the bucket for reportable finds, at "another club" he attends it has been discovered that people had been throwing away "Roman brooches and hammered coins" etc in them.
Photo: Bucket of rejected bits.