Sink rates of coins in different soils

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Blackadder43
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I know this is a bit geeky, but i am doing some research for a good friend and some of his fields are heavy clay, with some flint thrown in for good measure
To me this would indicate that coins wouldn't be able to sink very far due to clay and added obstructions such as flint
But some of his finds have been found at 8 inches plus
I would imagine its tried to be deep ploughed at one stage or another and needs another plough to bring things back in order again :ugeek:

But it got me thinking about sink rates in general, depending on the soil type or even sand on beaches

I remember an experiment that Thomas Dankowski once done on a beach
He was close to the tideline i think
He attached some dental floss to a mans gold band ring
He lay it on the top and within seconds it started sinking, it carried on sinking and he said it was a good idea to attach the dental floss else it may have been lost again lol
So at the fluid end of stuff like sand at the shoreline, it shows finds can sink deep, easily and very quickly, until i assume they hit the harder compacted areas of the beach
So beach detectorists need to know the make up and depth of the sands they are working on

Back to inland though
So at the top extreme we have the heavy clay and possibly flint areas
I imagine finds wouldnt really make it past 6 inches, even over hundreds of years, unless of course regularily ploughed, then its getting the right timing when finds are back in range again

But then you have the very soft loamy type soils like Holzhammer has been digging recently
With very little resistance i imagine that finds could sink really deep on their own, again dependant on whether ploughed often or not

Is there like a cut off point though?
Something along the lines of the coins own density compared to the soils density?
Going deeper into the soil i would expect it to get denser and more compact, which would stop the coin sinking any further if the 2 densitys started to balance out
What things change how far a coin can sink?
Its orientation?, like a coin on its edge would have a smaller surface to be able to sink further than a coin on its flat?

I know its a bit deep (see what i did there) and a bit geeky, but i've been on the jelly beans today and this type of thing keeps me from bouncing myself off the walls :lol: :lol: :ugeek:
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DaveP
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Earthworms - can turn over the top 6" in ten years dumping it all on top.
Wind - moves large quantities of soil in the UK.
Pasture or arable changes soil volume with increasing organic matter
Coin-sized and weight lithics 6000 years old sit on the surface while <100 year old coins are 6" or more deep.
etc.

it's a much more complex equation with many variables, especially the surface of the soil going up and not just the object going down relative to the surface.
Blackadder43
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Yea i did read about earthworms many years ago, amazing what those fellas can shift :thumbsup:
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Kenleyboy
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Interesting thread Blackadder :thumbsup:
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HolzHammer
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Kenleyboy wrote: Mon Nov 29, 2021 12:19 am Interesting thread Blackadder :thumbsup:
I agree!
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DaveP
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It's something the archaeologists have looked at in various forms over the years and there's plenty of published research for your friend to read up on.

Add to that, metal detecting is a highly biased and very limited measurement technique most probably giving a very skewed interpretation. And, I suspect it will be difficult to find any land that hasn't had the top 6", or deeper, ploughed in the last 100 years causing mixing of the desired detecting targets.

The paper in the link below does talk about terminal depth (word search terminal) and has cited references so probably a good place to start.

https://www.researchgate.net/publicatio ... il_context
Metalurgy
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FWIW,I remember some time ago,on a different forum, Allectus saying what a load of old cobblers this subject was,or words to that effect.
My permissions are almost all heavy lias clay and the deepest items that I find,consistently,are lead and buckles,occasionally there is the odd surprise but most of the best finds are relatively shallow.
I have a permission on peat where the signals go deeper and louder,probably the moisture in the ground causes that.
Pete E
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I used to shoot (with a rifle) over one of the farms I detect over today. I was very keen on my shooting and even collected my used cartridge cases to reload with new powder etc, and use them again. Occasionally one would go a drift, and roll forward to today and every now and then, I will detect and dig one of these errant cases..

In "normal" pasture soil, I find them around the 6" mark, but one or two have been as deep as 8" and 10"....These particular fields have never been ploughed in that time although they are rolled with a heavy roller every few years.. the field is mostly grazed with sheep or calves, rarely with cattle....

Finding cases at 10" after 25 years indicates to me one of the reasons why I find so few medieval or older finds on this ground.....
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Easylife
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A great subject which could be divided into say pasture, cultivated and woodland? In woodland the ground is generally not only drier but also builds up over time from organic matter, so older targets can get buried deeper rather than sink!
Most of my permissions are pasture and soil depth limits how deep any targets can sink.
On a 5 acre pasture field on a hill the soil is no deeper than 10" before the dense clay layer. It was previously ploughed at some time but nothing ever sinks into the clay. I have found horseshoes and hammer heads sitting flat on top of the clay layer there, it is pretty impeneterable even when damp.
On my main pasture permission the landscape is quite variable though I would say that the soil is about 14" deep before the clay layer and I have been figuring that one out for over 4 years. I'm not sure when at least some fields were last ploughed but guess it will be 1940's or later. All Victorian finds and older are about 8" deep or so and it is very rare for any target to be in the first clod out. I did have a 1970's 2p at 4" deep so could maybe say an inch for every 10 years in the top bit? A hundred year old coin here will be at about 6" deep and older coppers generally at about 8" or so, though cartwheel pennies always seem to be at about 10" deep or so.
In Summer the ground here is generally too dry for anything to really move but in Autumn/winter time no doubt there is some target movement in the softer ground. The density and footprint of an item are no doubt a main factor and large lead targets are usually the deepest finds. Though hammereds tend to be at 6 or 7" regardless, I really don't feel that they naturally move much at all due to their lightness. The pasture is generally quite dry most of the time and it takes a lot of prolonged rain to penetrate beyond 6" deep though that can still dry out pretty quick.
I often wonder how deep the finds would have been if the pasture had never been ploughed at all, shallower or deeper? It seems to have been deep ploughed at some point in the 1900's, and it's pretty dissapointing to go to the extra effort of digging into the deeper dry soil to only find part of an aluminium can at 12" deep, which didn't get to that depth if by sinking at all?
If only there was a single field which had never been ploughed to compare find depths to, but there is not here so it just is what it is! But the odd thing is that none of the keepers are ever plough damaged, and we are talking of hundreds of copper coins including a lot of blank older ones. Any casual losses were more at risk of damage from cattle hooves, though in soft ground they likely pushed targets deeper.
Whether atop the hill or down in the water meadows the soil firmness is key to just how fast targets sink as well as target size and metal density, though as said usually the dense clay layer is the limiting factor in my own pasture experience.
On the slope the soil naturally moves downhill especially when ploughed, though it never seems to uncover deeper older finds at the field top, maybe they moved down hill with the soil? I guess that the stones don't generally sink in the soil due to their density being similar to that of the soil?
On a campsite I dug about 60 one pound coins date ranging over almost 40 years and they were mostly just 3 or 4" deep with just the odd one at 6" max. A Georgian coin there was at 8" deep. So in my pasture experience I would say that after the first 6" that nothing is likely to be moving too much at all due to the likely quite dry ground, though conditions can vary.
Depthwise my most unexpected find was a 4th Century Roman siliqua at just 4" deep almost right under a 200 year old hedge, so that seemed a bit odd but we will never know why and there are just too many possible factors to draw any conclusion.
Cultivated ground is just like everything being regularly thrown into a mixer and then spread back on the fields.
I find it quite amazing just how much certain ground levels can increase over a very long time, a Roman road being found at 5 metres below current street level is maybe a more extreme case?
:Thinking: :thumbsup:
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Littleboot
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The thing is, within a very small area soil/ground conditions can vary immensely. My permissions generally range around my house in all directions from a few yards from my door to about 5 kms. The bedrock is in some places breaking the surface and in others the soil is feet deep. Even in my own field there are deep and shallow patches. (And don't forget Mr Mole. We regularly move several barrowloads of soil brought up by the little blighters. lol)
Thing is though that I know the depth of my machine and although I will waft over the deep alluvial stuff in the valley bottom en route to somewhere else i rarely find anything of any age and I know that doesn't mean it isn't there. Hence, when the farmer gets his ditching bucket on the scene I am there like a rat up a..well...ditch. :lol: Otherwise, the vast bulk of my finds come from areas where things have a stopper on sinking out of range. Whether that is bedrock near the surface, or stony ground caused by either geology or old buildings and tracks.
Thing is though, there isn't much point mithering about stuff out of range. Most fields where people say there is nowt to be found tend to simply be where finds drop out of range. So unless something changes that (aforementioned farmer digging with his machinery) then it is not somewhere I make a beeline for. My soil is mostly clay and flint, with some black alluvial in the valley bottom naturally. The ratio of finds drops off dramatically when I get in the black stuff.
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Earlier this year a new water supply was dug across a field and after the topsoil was stripped I went in to detect.
Luckily I found a cut half and a Richard 111 halfpenny. They were more or less on the top of the clay,the top soil wasn’t much more than 6” deep.
I’ve only found modern rubbish and coins in this field,apart from the odd buckle,however,it’s right next to a field with a villa but I haven’t found anything Roman.
I’m certain there’s finds to be found but my finds god is turning a blind eye.
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Charles Abbeyville
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This is a particularly interesting subject and worthy of as much input as possible. It doesn't help much that a farmer I discussed this with couldn't grasp what was going on under the surface. He said "I plough the same fields every year, year after year and suddenly a huge stone reaches the surface and breaks something on the plough".

Personally I lost my little finds pouch once, about 10 years ago now, it had a Saxon strap-end in it and we have never managed to find it since. This field is 100% not night-hawked. :clapping:

On one of our now 'quiet' fields my mate rightly says "you can't find it twice", how right he is and yet we have a roman site here that has been detected for 40+ years, Hundreds of detectorists used to come here from all over the country and finds were plentiful. Here's how much it was detected in those days... the farmer would plough his field to open it up to the weather for the winter and within a couple of weeks it was flat as a pancake! He's a decent farmer but even he had to put a stop to it because he was unable to work his land properly. Now then, you would think it would now be another 'quiet' field but we could go on there today and still get about 15+ roman off. Now there's a field that turns all my theories about the mechanics of ground movement upside-down.
How come my heavily detected Saxon field (only me and my mate on it for last 35 years) might nowadays give me one find a week if I am lucky but this roman site still gives so well????

Coins, stones, shotgun shells seem to go up and down but I don't know how or why. Is it worms, rabbits, moles, probably some or all of these in some fields.

I hope this thread keeps going. :thumbsup:
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