OK - Do Coins Sink or Not?

[kingingkunsan]

Ok. I will throw my hat in. Found this while researching the topic. Take it for what its worth, I am no expert
ABOUT COIN DEPTHS

Why are some older coins very shallow when newer coins are deep at the same sites? How can a new coin sink deeper in a few years than an old one in over 80 years?

The Density of Soil

The density of inorganic soil is from 2.6 to 2.8 and any object of greater density, including coins, would eventually sink until the density of the soil equaled the density of the object.

The Sink Rate

The sink rate is determined by the difference in density, the greater the density the faster the sink rate. Contributing factors are vibration, rain, frozen soil, grass buildup, leaves and a few others.

How often the ground gets saturated can be a much bigger driver of coin depth than any minor differences in soil density. Until the ground directly beneath the coin becomes saturated to the point where the dirt becomes suspended in the water, and can move to the sides of the coin due to the coin weight, then little depth due to sinking can occur.

That's why many coins seem to end up in the 6-8 inch range - it takes a real soaker to move them deeper. So maybe the discrepancies in coin depth can be attributed to minor differences in the local drainage. The finer the soil particles, the easier they get suspended and the faster the sink rate.

Chart of Densities

Here is a chart of the densities of some of the common metals we find with metal detectors, also the differences in the density of different metals and a major difference between most of them and soil.

Looking at the chart below, the dime should sink a lot farther than the penny, because the gravity is twice as high on silver as copper is? I know I've found silver just under the grass and then dug 6" or 7" for a clad penny. Nothing worse than getting a deep signal, dig it and it's a clad penny!

The good stuff is sinking faster than the trash. No wonder not many gold coins are being found!

Density of Precious Metals

Platinum 21.45

Gold 19.3

Silver 10.5

Copper 9.0


Densities of Some Common Metals

Aluminum 2.7

Lead 11.4

Magnesium 1.8

Steel 7.8

Tin 7.3

Zinc 7.1

Iron 7.87

 

[upnorth]

I was flabbergasted to learn as a young man in EOD school that bombs that are dropped from aircraft and fail to explode can be found about 5 feet deep in sand and over 100 feet deep in clay. We learned to sink a shaft in the clay and the digging was TOUGH!
Once they've reached these depths, they do not sink further. It's their initial velocity and of course weight that gets them sunk.
Bottom line: coins are going to stay where they've been dropped unless the critters, frost, etc. disturb them and of course they'll slowly get covered over with leaves, grass, dust, etc.

Yup. I found a group of fur trade knives below the plow line in a wet low point in a field, they were just a whisper on the machine and REALLY deep. Likely buried a couple hundred years ago then the blow dirt and vegetable matter etc. put another foot of earth on top. I also found a trade metal rod used to break open beaver dens (not a damaged musket barrel). It was flattened\flaired and had teeth filed into the end for use as a flesher. That was no deeper than 8-10 inches. However it was on the edge of a naturaly redirected tributary stream. So this item from the same time period was much shallower as the soil was scoured away by spring floods now and then. I believe that objects bury primarily through soil accumulation, with a few minor variables.

 

[GeorgeinSC]

I have seen this information at more than one source. Found this on another forum and thought that I would add it to the discussion.




ABOUT COIN DEPTHS

Why are some older coins very shallow when newer coins are deep at the same sites? How can a new coin sink deeper in a few years than an old one in over 80 years?

The Density of Soil

The density of inorganic soil is from 2.6 to 2.8 and any object of greater density, including coins, would eventually sink until the density of the soil equaled the density of the object.

The Sink Rate

The sink rate is determined by the difference in density, the greater the density the faster the sink rate. Contributing factors are vibration, rain, frozen soil, grass buildup, leaves and a few others.

How often the ground gets saturated can be a much bigger driver of coin depth than any minor differences in soil density. Until the ground directly beneath the coin becomes saturated to the point where the dirt becomes suspended in the water, and can move to the sides of the coin due to the coin weight, then little depth due to sinking can occur.

That's why many coins seem to end up in the 6-8 inch range - it takes a real soaker to move them deeper. So maybe the discrepancies in coin depth can be attributed to minor differences in the local drainage. The finer the soil particles, the easier they get suspended and the faster the sink rate.

Chart of Densities

Here is a chart of the densities of some of the common metals we find with metal detectors, also the differences in the density of different metals and a major difference between most of them and soil.

Looking at the chart below, the dime should sink a lot farther than the penny, because the gravity is twice as high on silver as copper is? I know I've found silver just under the grass and then dug 6" or 7" for a clad penny. Nothing worse than getting a deep signal, dig it and it's a clad penny!

The good stuff is sinking faster than the trash. No wonder not many gold coins are being found!

Density of Precious Metals

Platinum 21.45

Gold 19.3

Silver 10.5

Copper 9.0


Densities of Some Common Metals

Aluminum 2.7

Lead 11.4

Magnesium 1.8

Steel 7.8

Tin 7.3

Zinc 7.1

Iron 7.87

__________________
White's ProXL 6000, Technetics T2

 

[JimGilmore]

I've said this before and I will say it again....
Coin can only sink a small amount.
Most of what people refer to as sink is the growth of thatch and new material that falls upon them.
Depending where yoyu are and how much water your area gets...thee will move LIke gold does. But they are not as heavy as gold so they will not go as deep as gold.
If you have water and movement like earthquakes they can only sink to a point where the heavier stuff will still be under them. And because of the shape and size of coins they are limited in the depth they reach because their size will make them bouyant.
If you were to take a plastic shoebox. and grow grass in it I highly doubt that any coins dropped upon the grass would eventually sit on the plastic bottom of the box.

 

[JimGilmore]

uhm...as a direct reply to GeorgeinSC.
Do not confuse gravity with weight.
Yes gold is heavied than aluminun.
But Gravity does not PULL any stronger on one than the other.
THEY aill fall at the same rate.
If you doubt it go back to basic science classes.

How Items sink in soil requires movement(mostly Vibration) and lubrication(HYDRATION).
With out them THEY go noplace.
If you want to see a real good example of how the soil build UP not the coins sink. Go to an old park with sidewalk and water boxes for the sprinklers.
They are often lower than the grass and soil. Though they were NOT when they were installed. THe sidewalks were higher then the grass and soil but often you will find the sidewalks cut into the grass. They did not sink.

When You look at trees. Remember those roots grown around just like the trunk.
Sometimes the roots get exposed. But for the most part the soil build up around them enough to cover them.
So how much does the tatch grow each year ???
If you want to find a place to find meteorites I have a great place to look. Try any large tall building with a high roof that is flat. The larger the better. Not all meteorites come into and hit the ground at high speed. Sweep that roof off totally bare and come back in a week or two. You will find a lot of material. Some is from outta space. some is stuff the wind has lifted and dropped. How much depends on where you live.

 

[Steve O]

Gravity accelerates all things equally but does not pull all things equally....... the reason things have different weights.

 

[jabbo]

It depends on something, not sure what tho. In the woods where there is no foot traffic I found Indian head pennies at 1, 2, 3, 4, 5, 6 inches, and some even deeper. In the same woods some lead musket balls were only 3 inches but most were a good 5-7 inches deep. Don't ask me why cause I don't know.

 

[JimGilmore]

As I have said the difference is most likely moisture content of the area. With no fluid there is NO movement .With the exception of the soil being just soft sand the wind can move the sand to allow an item to sink.
And even in soft sand it takes moisture to move beyond a certian point. Because at some point the sand will be compacted.
Gravit pulls on everything EQUALLY. Again seems most people make assumptions and have problems with Newtons basic laws. Their different weights have nothin to do with how much gravity is pulling on them.
A ship does NOT sink because its Light. It floats because the weight is displaced over a area large enough to support it.. Even though it may weigh many tons.
some simple questions to try and make clear why the statment that gravity pulls differently on items is WRONG,
So does gravity pull differenty on 100 lbs of feathers than it does on 100 lbs of gold. Assuming we were to weigh them with the same system , Lets say we were to measure them both in troy pounds ???
Gold might be 19 times heavier than water but it can float.
The principles are all the same... Shape and size are the factors a gold ring will settle deeper than coins not because its heavier per say. But because it has less area that the soil is going to touch. But it will not sink unless there is hydration and vibration.

 

[Steve O]

Look it up Jim, you will see that gravity pulls objects differently because of their mass, again, that's why things have different weights. It's very interesting. Common sense is out the window because of the unseen forces at work.

 

[Robert2300]

So how come people find copins 10, 12 and 15 inches deep? Of course I
realize soil is often carted in and spread out over a development area and
graded, but besides that, how come they are so deep if they don't sink?
Robert2300

 

[Larry (IL)]

You must not have read the rest of the responses..... Most coins get covered up year after year, airborne dirt, decomposing leaves, grass, weeds, insect movement in the ground, rain, mud and probably dozens of other reasons that coins seems to sink. The being covered up theory is supported by the older the coin the deeper they seem to be........ in general. (We all know the exceptions to the rule)

 

[ecdonovan10]

Nice replay Larry(IL) you hit it on the head. Farm fields used to be deep plowed over a foot deep regularly, you really got new finds every year, now with no till (lazy mans farming) you don,t get new finds every year. I miss plowed fields.

Ed D.

 

[MarkCZ]

You must not have read the rest of the responses..... Most coins get covered up year after year, airborne dirt, decomposing leaves, grass, weeds, insect movement in the ground, rain, mud and probably dozens of other reasons that coins seems to sink. The being covered up theory is supported by the older the coin the deeper they seem to be........ in general. (We all know the exceptions to the rule)

Hay, Larry,
I find pull tabs sink at the rate as coins, even those beaver tail pull & toss ones. So if coins sink, how long will it take for new coins to catch up with the 5" deep pull & Toss tabs seeing how a coin is much heavier than a tab?
In our local park the fresh dropped 65-75 coins are in the same 3-1/2" to 5" depth range as the production date for the pull & toss tabs, 1965 through 1975. Fresh dropped silver is below that, with 1899 being very near 8" deep.

Mark

 

[Ed in SoDak]

It might not be merely weight, but also surface area. 100 pounds of gold takes a small space. 100 pounds of feathers, even compressed is more like a bale of hay in size. Take a pegleg pirate with a size 12 left foot. Which leg will sink further in anything but hard dry soil? A coin on edge can fall into a crack in dry soil. Wind accumulates leaves in random piles, so does heavy runoff. Snow pack holds things in drifts then releases them in place or elsewhere. Mud, silt coins on edge.

If it were 100% dead easy, all good targets would be already found!

-Ed

 

[Johnnyanglo]

In general,in the same soil:

1. The longer a coin is in the ground the deeper it sinks until it intersect a denser object than itself (rock, strata)
2. Sink rate decreases with increasing depth
3. The larger the coin surface area the slower the sink rate
4. The more massive (i.e. weight) the coin material the deeper and faster it will sink


Then, target shape, target surface area, and target mass combined with soil grain size and moisture content ultimately determine sink rate. Greater soil water content joined to smaller grain size permits greater downward mobility due to increased percolation.

At the same time coins are sinking, and at different rates due to their shape, mass, surface area, and time in the ground, the soil base height is also rising due to wind blown soil deposition, plant compost, sedimentation, etc.

Added to the normal coin sink rate and soil creation is the additional variable of insect turnover, winter heaves, frost/ice duration, earthquakes, flooding, liquefaction, rainfall rates, and man-made building and landscaping alterations.

Figure that the probability of the average detector finding a coin-sized object in inert soil decreases rapidly beyond 6-8". Past 13" your chances are almost nil for coin-sized objects, even in inert soil. For this reason coins are mostly found within the first half-foot of the surface; they exist further down but usually undetectable. Even the best detector is limiting by iron contamination and magnetic soil minerals. These can cut target maximum depths in half and in heavy minerals/iron the depth can be limited to 2-3" on coin-sized objects. The deepest and oldest coins are then likely to be out of reach especially in tougher mineralized soils.

It is correct that gravity pulls all objects with the same force (at the same radius from the earth's core). A foil gum wrapper and a dime have different mass (density per unit volume), and therefore the dime's mass will cause it to sink faster and further, though the gravity is the same for both.

When all the variables are accounted for, the general rule still holds true: the older the coin the deeper it will sink. However, with all the possible variations many exceptions will occur; where in some locales old coins will be near the surface and elsewhere clad sinks to 8-10. If you find an exception, stop and consider what may have contributed to it.

If you find a crushed coke can at 14" make a logical deduction that it didn't sink to that depth(light mass and large surface area are obstacles) but was likely dropped and then fill-soil added afterward. That isn't good news for you, since the oldest coins will be well below the detectable level. If you find exposed tree roots or a dirt mound around tree bases, deduce that the soil has eroded somewhat but has not seen additional fill added- which is good. If the soil is densely packed, the packing may assist in decreasing the coin depth through compaction, increasing the chance of recovery. At a construction site where the sidewalk has been removed you can calculate that due to sparse moisture under the cement the coins will be shallow, even if they sit for a hundred years they aren't moving much.

Since soil conditions (grain size and water availability) can change drastically over short distances, there is no single sink rate but rather many different ones. Once you've dug into the soil and recovered some targets you can begin to make educated guesses where and how deep the oldest (most valuable) coins should be found. In other words, we aren't passively just sweeping the coil in a pointless endeavor while whistling a happy tune, but analyzing the situation and thinking deductively to give yourself the best chance of finding the deepest coins (or relics).