gold nugget simulation?

[Skippy]

Here's how to measure the volume, and also the density, of your nuggets ( and un-hallmarked jewellery etc ).
See the attached photo:
A ) Place a small container of water ( 20 - 50 cm³ ) on your scales, and 'Tare' the readout to zero.
B ) If you're wanting the weight of the item, place it alongside the water container, and take the reading as indicated.
C ) Using monofilament fishing line / polyester sewing thread / very fine wire, lower the item into the water, so that it is just submerged, and not touching the bottom or sides of the container. Make sure there's no air bubbles attached. Take the indicated weight reading.

Reading C is the weight of the displaced water, which, because water has a density of 1.00 g/cm³ , it's also the volume of the water in cm³ .
To calculate the density, divide the weight in reading B, by the weight in reading C.

So in the example, the finger ring weight = 9.50 grams. The volume = 0.92 cm³.
The density calculated as 9.50 / 0.92 = 10.33 g / cm³ which is typical for Sterling Silver ( tech data usually gives a figure of 10.36 )

For Green's nuggets, he will have to tie the thread to them, no doubt tricky. Fishing line is stretchy, so tends to hold onto objects when tied on. Copper wire won't do this, and polyester thread is a bit thick, though it can be unravelled to use its individual fibres.

[green]

Here's how to measure the volume, and also the density, of your nuggets ( and un-hallmarked jewellery etc ).
See the attached photo:
A ) Place a small container of water ( 20 - 50 cm³ ) on your scales, and 'Tare' the readout to zero.
B ) If you're wanting the weight of the item, place it alongside the water container, and take the reading as indicated.
C ) Using monofilament fishing line / polyester sewing thread / very fine wire, lower the item into the water, so that it is just submerged, and not touching the bottom or sides of the container. Make sure there's no air bubbles attached. Take the indicated weight reading.

Reading C is the weight of the displaced water, which, because water has a density of 1.00 g/cm³ , it's also the volume of the water in cm³ .
To calculate the density, divide the weight in reading B, by the weight in reading C.

So in the example, the finger ring weight = 9.50 grams. The volume = 0.92 cm³.
The density calculated as 9.50 / 0.92 = 10.33 g / cm³ which is typical for Sterling Silver ( tech data usually gives a figure of 10.36 )

For Green's nuggets, he will have to tie the thread to them, no doubt tricky. Fishing line is stretchy, so tends to hold onto objects when tied on. Copper wire won't do this, and polyester thread is a bit thick, though it can be unravelled to use its individual fibres.

Interesting, learn something new. Interested in how volume and density of my nuggets would help select a simulation(standard)target for gold nuggets.

My thoughts, maybe correct maybe not.
Nugget TC is the most important.

As Carl has mentioned before:
Response conductivity is due to target metal type.
Response inductivity is due to target thickness.
Response strength is due to target surface area.

Which means that the inductance is mostly controlled by the skin effect (which depends on target thickness), and resistance is mainly controlled by the conductivity. Both target size and shape have an effect on the inductance and resistance. Therefore, although you only need to have the correct value of tau for modelling purposes, the problem is essentially a matter of figuring out what the tau needs to be. Which is why you'll not see any hard-and-fast numbers published anywhere.(reply #16) I posted some TC numbers for the three nuggets I have http://www.geotech1.com/forums/attac...18142660(reply #40) four years ago. Still haven't seen any other nugget TC's posted. The nuggets I have aren't hard to detect so I posted a reply #135

Nugget sizing info:

We are often asked how many pieces per gram or ounce. It is very hard to predict how many pieces there are per gram or ounce as the # of nuggets by weight varies quite a bit per batch. But in general you can expect around 1-2 pieces of gold for 4 mesh, 2-4 pieces of 6 mesh per gram, 7-12 pieces of 8 mesh per gram and around 15-20 per gram for 10 mesh. You can expect many more pieces for smaller 12 (around 20-25), 14-16 (around 30-50 or more) pieces and hundreds for fine gold. Every batch is very different and each piece of gold is natural and of course therefore unique. Some may be flat and light or rounded and very dense (heavy).

How small a nugget can a good PI detect? What mesh size would make good test targets for smaller nuggets? 8 mesh, 10 mesh, both or other?

Any guess on typical TC for 8 or 10 mesh nuggets.Didn't get any replies so I posted question in another forum.https://www.detectorprospector.com/forums/topic/8191-nugget-mesh-size/ (got a lot of information)suggesting 8 mesh might be the lower limit for a PI. He weighed a few 8 mesh and got one to four grains, my smallest is 4grains so I'm thinking TC is going to be less than 2usec(my 4grain nugget on edge). What would be a good TC number for 8 mesh nuggets? Someone could post some measurements, I could get 1 gram worth and measure TC's or we could guess a value(maybe 1.5usec)since each one would be different. I'm thinking three TC targets, 1.5 to 2, 4 to 5 and one 8 to 10usec. Was thinking about copper wire again. Think wire might make the most repeatable target. Would need to determine a good length for each of the three TC targets. Would depend on wire target detection distance being similar to some nuggets with the same TC.

Including another wire chart(diameter, SWG and AWG vs TC)are any of the easily available SWG or metric size wires in the(1.5 to 2, 4 to 5 and one 8 to 10usec.)range?

I find most PIs will hit 2-3 grain gold nuggets @ 1-2". Let's say 3-4 grains @ 3"(Carl's reply #142)reference point for wire length

[Skippy]

" I'm interested in how volume and density of my nuggets would help select a simulation (standard) target for gold nuggets.

Density doesn't help, that's just a useful by-product of the volume-measuring process, helpful if you're trying to assess whether an unhallmarked ring is 10/14/18 carat, for example. The lower the carat, the less gold, so the density drops towards the 'copper' zone. Compare measured density with known reference figures to judge the carat/fineness.

Volume is needed in order to make replicas of similar volume, and hopefully similar detectability. Physical measurements would also be handy, so we can come up with representative form-factor, and not plain spheres.

I'm thinking your smallest one is quite spherical ? That may be tricky to 'tie up', maybe physical measurements with calipers is all that can be done with that one.

[green]

" I'm interested in how volume and density of my nuggets would help select a simulation (standard) target for gold nuggets.

Density doesn't help, that's just a useful by-product of the volume-measuring process, helpful if you're trying to assess whether an unhallmarked ring is 10/14/18 carat, for example. The lower the carat, the less gold, so the density drops towards the 'copper' zone. Compare measured density with known reference figures to judge the carat/fineness.

Volume is needed in order to make replicas of similar volume, and hopefully similar detectability. Physical measurements would also be handy, so we can come up with representative form-factor, and not plain spheres.

I'm thinking your smallest one is quite spherical ? That may be tricky to 'tie up', maybe physical measurements with calipers is all that can be done with that one.

I'm thinking your smallest one is quite spherical ? picture http://www.geotech1.com/forums/attac...7&d=1418142660


Think I could tie to it. All I have at the moment is reloading scale that might work. Was looking at digital scales, might order one after holidays.
The 18 grain nugget on edge has the same TC as the 4 grain nugget flat and about twice signal strength. Might detect about 1 inch deeper with a 8 inch coil, maybe over 3 inches deeper if both laying flat.

[waltr]

" I'm interested in how volume and density of my nuggets would help select a simulation (standard) target for gold nuggets.

Density doesn't help, that's just a useful by-product of the volume-measuring process, helpful if you're trying to assess whether an unhallmarked ring is 10/14/18 carat, for example. The lower the carat, the less gold, so the density drops towards the 'copper' zone. Compare measured density with known reference figures to judge the carat/fineness.

Density is an indicator of the purity and the purity has a large effect on the conductivity of the alloy.
Conductivity then has an effect on the eddy currents.

[Skippy]

True, but it doesn't help with the modelling, or dummy-nugget creation process. This is because the detectability and time-constant is what we are attempting to mimic. These are influenced by other factors such as voids, inclusions, cracks, crystal defects, in addition to the conductivity.

[Ferric Toes]

True, but it doesn't help with the modelling, or dummy-nugget creation process. This is because the detectability and time-constant is what we are attempting to mimic. These are influenced by other factors such as voids, inclusions, cracks, crystal defects, in addition to the conductivity.

Detectability and time constant are affected by the purity of the gold. I did tests ages ago on gold/copper and gold /silver standards. Even 5% of other metal, even if a good conductor, when alloyed with 'pure' gold has a dramatic effect on TC and detectability.
Nuggets from South Australia are of purer gold than those from Western Australia, which have a higher silver content. A hypothetical spherical nugget of say 1.0gm would be less detectable from W. Australia than a similar one from S. Australia.
Personally I don't see a solution for creating a dummy nugget as there are too many variables, which include the other features you mention above. I have a 1.6gm nugget that quite undetectable on one of my 10uS delay units. Under a lens it has a sponge-like structure.

Eric.

[Skippy]

Yes, all nuggets are different, I'm not trying to make a perfect replica of one specific nugget, or 10 specific nuggets.
I'm trying to help Mr. Green and others come up with some things representative of some plausible real nuggets, that are ideally easily made/found, reproduceable, universal. The purpose being comparison tests, detector settings evaluation, etc.
We don't really have nuggets here in the U.K, so I'm not actually bothered about the subject, but other people, like 'Detectorbits' clearly are.

I'm hoping to apply some of the 'maths' to other items in the future, this is just part of the science experiment, which hopefully yields something worthwhile.

[Ferric Toes]

Yes, all nuggets are different, I'm not trying to make a perfect replica of one specific nugget, or 10 specific nuggets.
I'm trying to help Mr. Green and others come up with some things representative of some plausible real nuggets, that are ideally easily made/found, reproduceable, universal. The purpose being comparison tests, detector settings evaluation, etc.
We don't really have nuggets here in the U.K, so I'm not actually bothered about the subject, but other people, like 'Detectorbits' clearly are.

I'm hoping to apply some of the 'maths' to other items in the future, this is just part of the science experiment, which hopefully yields something worthwhile.

Here is an idea that may be of interest. When testing industrial metal detectors, metal spheres of different sizes are used. We had a set from 10mm diameter to 0.5mm embedded in plastic rods. I don't have them any more, but I do have left some 4mm diameter phosphor bronze ball bearings which weigh 0.3gm. These are quite detectable with a sensitive PI and there are no orientation problems.
Not knowing if it were possible get these now, I typed a request into eBay and came up with a result. A company specialising in model engineering/live steam have two sizes, 1/8" and 3/32". They come in packs of 10 and are inexpensive. They also do stainless steel balls 3/8", 3/32". I am going get packs of each size to test and plot decay curves.

Eric.

[Skippy]

I'm curious as to whether Mr. Green will be able to get worthwhile volume measurements for his smallest two nuggets, the weight of water displaced is going to be about 0.02 gram for the smallest one, so without scales reading to 0.001 gram, we only have physical measurements ( calipers, micrometer ) to go by.
So these 'reloading scales' are for measuring powder in ammunition ? But they're old-style two pans and a pile of loose weights?
I've been playing with some estimated figures, with interesting results, but some real physical nugget dimensions would help. The only pic I've found is them presumably lying flat-on, with no indication of the thickness.

[green]

I'm curious as to whether Mr. Green will be able to get worthwhile volume measurements for his smallest two nuggets, the weight of water displaced is going to be about 0.02 gram for the smallest one, so without scales reading to 0.001 gram, we only have physical measurements ( calipers, micrometer ) to go by.
So these 'reloading scales' are for measuring powder in ammunition ? But they're old-style two pans and a pile of loose weights?
I've been playing with some estimated figures, with interesting results, but some real physical nugget dimensions would help. The only pic I've found is them presumably lying flat-on, with no indication of the thickness.

First. Your reply #158 is my thought exactly. I don't live near gold either, just a science experiment and hope to learn something. Don't know how to determine if detector is good without a reference. Carl has his 1x1 foil, lead shot, solder targets and others to judge the detector he is working on. What he hasn't shared is desired detection distance for the different targets and applications. I read detecting a 10inch US dime should be easy, don't know how it could compare to detecting a 2grain nugget with a 1.5usec TC.

Your reply #150 suggested needing .01gram resolution. My smallest nugget is 4grains=.259grams/19.3=.0134grams of water if nugget is pure gold. I'm calculating wrong or need .001gram resolution?

Was wondering dimensions for different weight nuggets. Made a chart varying thickness for square nuggets assuming pure gold. Thinking if target not square or lighter than gold it would be easier to detect if TC's were the same.

[lytle78]

What about the ball in the end of your garden variety Bic ballpoint pen. Standard - universally available...

[green]

What about the ball in the end of your garden variety Bic ballpoint pen. Standard - universally available...

http://www.geotech1.com/forums/showt...663#post244663 I looked for a Bic pen. Not all Bic's looked the same, not sure which one to purchase and try.

[Skippy]

I've estimated your nuggets 7,8,9 as having volume = 0.016, 0.040, 0.074 cm³, hence metric scales with resolution of 0.001 gram would be best. I originally asked if you had 0.01g res. scales as I didn't know what you had, it may have been a jewellery scale, weighing in 0.1 grain increments, for example.

I assumed you were a very occasional nugget-hunter, or were at least planning a trip at some point, hence your desire to do some preparatory ground work.

One of the problems with the Bic pen ball, is that Bic don't make 20, 40 and 60 inch long biro's, with proportionally larger balls for us to salvage. Our test targets are going to be a series of 'nuggets' with different 'ease of detection' , having just a single one is of limited use.

[Skippy]

...... some real physical nugget dimensions would help. The only pic I've found is them presumably lying flat-on, with no indication of the thickness.

In the absense of a reply, I've gone ahead and made some estimates, so we can get going on this.

Nugget 7 was modelled as a disc 3.5 mm diameter, 1.7 mm thick.
Nugget 8 was modelled as a disc 5.0 mm diameter, 2.0 mm thick.
Nugget 9 was modelled in two ways:
9A: a disc 7.0 mm diameter, 2.0 mm thick.
9B: a disc 4.5 mm diameter, 2.0 mm thick.

These have volumes of 0.016, 0.039, and 0.077 cm³ for nuggets 7, 8, 9A.

9A assumes the area, of 12 x 4.5 mm is circular.
9B works on the idea that the 4.5 mm dimension is the one limiting eddy-current flow, and the length of 12 mm mainly contributes to the strength of response. This is much like Green's copper wire tests - the small dimensions of the wire diameter dominate.

Now for the Time-Constant modelling.

In previous threads on modelling, we tested square targets, such as aluminium drinks-can sheet, and we came up with a formula showing how Time-Constant, dimensions, and electrical conductivity were related:

T-C = 0.072 x D x T x %IACS

Where T-C was in microsecs
D was edge length in mm
T was thickness in mm
%IACS is the conductivity relative to a figure of 100% for pure copper.

This needs to be modified to suit circular targets.
I did some simple mathematical modelling of L and R for a square vs circle, and came up with an approximation:

A square target 1.00 units across is equiv. to a circular one 1.205 units diameter

and so:

A circular target 1.00 unit diameter is equiv. to a square one 0.83 across.

This results in a first attempt circular target model:

T-C = (0.072 x 0.82) x D x T x %IACS = 0.060 x D x T x %IACS

I then tried this out on real targets. I chose cupro-nickel coins, partly as a hunch, partly as I have more confidence in my T-C values, the lack of skin-effect means my 13kHz VLF is more accurate. Coins tried were US 5c 'nickel', UK large 50p, small 50p,and 20p.
I'll save the details for another time ... but they were pretty close, indicating the '0.060' figure in the model was in the 0.05 to 0.06 range.
So for the purposes of nugget modelling, I'm assuming the 'disc' model is:

T-C = 0.055 x D x T x %IACS

Applying this to the physical nugget models, and using the measured time-constants Green quoted for 'flat-on' and 'edge-on', I calculated %IACS figures of:

Nugget 7: T-C = 2.9 / 1.9 us; %IACS = 8.9 / 5.8 %
Nugget 8: T-C = 6.6 / 3.6 us; %IACS = 12.0 / 6.5 %
Nugget 9A: T-C = 5.4 / 2.9 us; %IACS = 7.0 / 3.8 %
Nugget 9B: T-C = 5.4 / 2.9 us; %IACS = 10.9 / 5.9 %

Points to note:
* These are LOW, down in the lead / cupro-nickel range.
* The long nugget9 is best modelled as a small one, the conductivity figures match the other two's better.
* My hunch was based on work done making 'dummy dollars' over on Dankowski's Forum. These are replica US gold 1 Dollar coins, which are 0.900 fine, but have %IACS figures about 15%. My dummies were made from lead-free solder, close to pure Tin.
* Though Carl M. never backed up his reasons for using lead shot and solder blobs (he should've), I felt he was close, based on my tests with lead-free solder, and the fact he should know what he's doing ....

So ... how to make some trial targets ?
Suitable metals that are easily obtained, and their %IACS figures include:

about 14% : 10,20,50 EuroCent coins, aluminium-bronze
about 14% : some lead-free solders
11.5% : 60Sn / 40Pb electronics solder
8.4% : lead
about 8% : UK 20 pence coin, Cu-Ni, (16% Ni)
5.3% : CuNi25 coins, eg. US 5c, UK 50p large / 50p small

I reckon lead-free solder ; pure lead; and CuNi25, covering the top/middle/bottom of the range, would be a place to start.

I'll think about the details and post tomorrow.

Attached pics of the models: