Wednesday, April 18, 2012

4/18/12 Report - Weight, Density or Shape

Written by the Treasureguide for the exclusive use of

Modernistic Crucifix Metal Detector Find

What surprised me most about this dug medallion is that the corpus is attached to the background at the feet and hands with pegs, more like what you would see on a very old crucifix.   This one appears to be very modern though.

It is 18k and about 2.5 inches tall.   Nice heavy bail.

Today I want to correct a statement that I have read  hundreds of times.   The statement is that gold sinks quickly because of its weight or density.   That is true when other things are equal, but they never are.

You can think of the movement of objects on the beach or in the shallow water as being something like the movement of gold flakes or nuggets in a gold pan. Water movement, gravity and the forces of nature move objects around on the beach and in the water separating denser objects from less dense objects.  Again, that assumes other things being equal when they never are.

 Often people say "heavy" objects when they actually mean "dense" objects.   Weight and density are different though.

When an object is on the beach or in the shallow water, there are other factors - the shape of the object being one very important factor.   The shape of the object is a very important factor and can cause very dense objects such as gold to sink more slowly than some objects that are less dense.    Under field conditions, shape is more important than either weight or density.

When the force of water acts upon an object, if the object presents a lot of surface area to be acted upon it will be moved more.  Think in terms of pounds per square inch of water pressure.
As you know lead is a relatively dense material, yet I've found lead sheets in shell piles along with thin pieces of aluminum,, pot shards, and of course, the shells.   The same goes for copper sheets.

A very thin sheet of gold (paper thin, for example), or any material, can be moved by the water more like you would expect a much lighter material to be moved.   The large surface area presents a lot of area for the water to act upon. 

Thin sheets of heavy material will also not sink into the sand so quickly because of the amount of surface area.

Most rings present little surface area to be moved by water and so are not moved by the water a lot, and tend to sink relatively quickly.  A medallion made of the same amount and purity of gold will not sink as quickly as a thin gold band.

Coins tend to lay flat on the sand.  When a coin lays flat on the surface of the sand and perhaps sinks a little, the water will usually rush over the coin as the main force of the water only has the edge of the coin (little surface area) to push against.

I am trying to simplify here without being wildly inaccurate.  I just can't include all the different factors and considerations.
Coins do sometimes flip though.  And also roll.

I think you will most often find that larger coins such as quarters will be closer to the waters edge, with nickels next, then dimes, copper pennies and then zinc pennies.  That is the often the case when there is what I've described as a coin line or coin hole near the water line.   Rings will often be even closer to the water or in the water.

Most rings, because of the shape, will not be easily moved by water easily.  

That is not what I started to talk about, but after I got into it I wanted to correct the notion that weight is why gold objects tend to sink more than many other objects.  Density is more important than weight, but the shape of the object is more important than the object's density.

What I started out to talk about is analyzing your finds to know where to look next.  I'll have to do that some other day.

Concerning that little anchor that I posted a day or so ago, Carl wrote in and said he purchased a key chain with an anchor like that on it back in the eighties at Fisherman's Wharf in San Francisco.  That is a good reminder that all finds have a bit of a  story behind them.

Treasure Coast Beach Detecting Conditions and Forecast.

Conditions are degrading.  With the wind from the south, some beaches will continue to build and some will have nice shell piles.  

The seas are relatively calm, running three feet  or less.  That makes it easy to detect out in the low tide zone.

There is no change in the predictions for the next week or so.  I'd continue to look for dips and continue to check out the low tide zones that haven't been heavily worked yet.  Or work the water where that is possible.

Happy hunting,