However, when something turns up made of the 'wrong' metal for the soil, then acids and whatnot make their way under the surfaces and what might have been a finely patinated sheen developing in the 'right' soil, turns to crumbly dust and becomes part of the soil encasing it, leaving behind a pitiful pitted and corroded thing whose aesthetics are only appreciated in consideration of its very survival.
This is such an object ~
It's brooch sized, and brooch is always what I've thought it to be. It has an iron pin that projects from the centre of the face that would have once held a circular mount of probably a small stone or metal decoration. The evidence of its shape can be seen as a circular area of lesser corrosion, which suggests either that the mount was lost long after burial, or, that it protected that area from wear in usage leaving a tough surface of unworn, unpolished and unscratched metal that the acids had a harder time getting under.
The red coloured corrosion is also identical which tells us that's its made of a very similar copper alloy, and this an alloy that whenever found in the general locality always turns out to be from items of metalwork of either the late Saxon or Norman periods. Later Medieval things are invariably green, and usually very well preserved indeed, whilst red-coloured things are always earlier, always in a parlous state, and are easily bracketed between datable colours of rot. Detectorists know these things instinctively, because we dig a lot of Medieval stuff, but little of it red-coloured.
Its status as an object is unclear. It may be a brooch, and brooch is the most likely thing it could be, however, the 'catch' ends are broken away, so its not clear if it's a catch plate or not. What confuses matters even more is the fact that there's the corroded traces of a thin iron plate under the bronze plate, and that means it must have been fixed to a larger iron object and may not be a brooch after all. Then again, it may have been part of a larger brooch still, and one of iron... But I've never heard of such a thing.
'13th-15th century' is the catch-all phrase used for just about everything, from buckles and tumbrels, to buttons and thimbles. That's George III, till now! Or the height of Turner's extraordinary artistic powers till Hurst's diamond encrusted demise, if you'd prefer things in art terms? Which this must be explained in...
It's as if people used and wore no metal objects whatsoever in the 160 years between 1066 and the Year of our Lord, 1216. And perhaps they really didn't, because there's precious little of it known to make comparisons with here.
This style of decoration was the height of fashion in the twelfth century and adorned only expensive imported goods from Europe, and mostly from Limoge, so far as we know. It is not English work and certainly not provincial in any way— even though its surface now looks crude, that is only the effects of the corrosion — and it would once have been a very fine thing of high style, whatever it actually was to begin with.
Such decoration is also very rare indeed in this country. There's not a single equivalent instance recorded of any contemporary object decorated with this very particular and precisely dateable kind of vine scroll ornament that I can find on the entire PAS website, and there's only the one on UKDFD which out of interest, is made of the same kind of alloy.
Given such rarity, two items decorated with it from the same parish would be remarkable enough, but I have a further example in the form of a buckle plate found in the same place and of course, it's reddish brown in colour so it's made of the same alloy too. Its style is less curvaceous though, but I've no doubt it's the same date.
They are remarkable things, though, despite the corrosion. What a shame that the alloy reacts the way does — under suitable conditions this odd little thing may have come from the ground as a beautiful decorated golden disk with deep green patinas where the gilding had rubbed to the bronze. What we have though is merely an historical object whose significance will only ever be apparent to scholars, but forever invisible to everyone else.
12th Century gilt-copper brooch or mount, decorated with vine scroll ornament. Dimensions 24mm diameter. Epping Forest District, Essex.