gold nugget simulation?

[green]

Regarding that Cupro-nickel disc of Eric's, I came across this small graph showing how nickel percentage affects resistivity of Cu-Ni alloy:

... from which you could take a reading of 0.475 for 43% Ni alloy. This translates to conductivity = 2.1 x 10⁶ ; or 3.6% IACS, as Mr Hocking indicates.

Also, reading up on Lead, it's surprising how common it is to alloy it with a small amount of Antimony, and even 1% Sb can significantly alter the conductivity reading, dropping down the IACS figure from the pure 8.4% to the mid-7's.

Some charts with US Nickel and US clad Quarter. Was trying to understand stacking effect. Been posting Nickel TC at 10usec, got over 16usec today. Maybe didn't chart long enough decay before drawing decay line(10usec TC)? Depending on number of coins, delay time for straight line linear-log decay needs to be 1 to 2 times TC. Stacking double number of coins didn't double TC, would doubling thickness double TC? Been using TC=T mm * D mm * %IACS * multiplier. T * D for the Nickel and Quarter are close to the same. Made with the same material. Why is the Quarter TC 9 times the Nickel TC?

Duh. Clad to a core of 99.5% copper core.

[Skippy]

Presumably this 'stacked coin' stuff is to do with Eric's meter , and not nugget simulation?

How are you getting on with your nugget dummies ?

Now Christmas is sort-of out the way I can get back on with this, get my nuggets made, repair my test detector, have a think about skin effect, and have another attempt at pinning down the TC vs. T/D/IACS equations for thin targets.

[green]

Yes, Eric's meter. Trying to understand some things.

Have some ideas to try for nugget dummies. Hopefully soon.

[green]

Tried some things. What didn't work. Drilled 3.57mm hole in aluminum and steel, poured hot lead in hole. Couldn't get lead out, what I expected. Drilled hole in (2) craft sticks glued together, melted lead in hole with soldering iron. Would be a good way if wood didn't burn and hole enlarge. Would leave lead in wood sticks and sand for desired thickness. Did more searching for lead shot. Still haven't found away to purchase smaller amounts. Thought about a box of 12 gauge but one person suggested shot size varied some and was maybe 1 size off. Thinking aluminum kitchen foil(thickness variation?) or copper wire(most repeatable) unless Skippy finds a good way to make a target. Maybe someone else has a suggestion, where to find lead pellets(how pure is the lead from shot shells or fishing shot?) or how to make repeatable targets.

[green]

Two foil targets that might work for 1 to 2 grain nuggets. 4x4mm 4layer probably best. Foil was cut 2 times desired size and then folded twice.

Folding foil around a needle or straight pin works best for me.

[Skippy]

Do I have any ideas? ....
The best one so far that's useable on lead and any solder type is to make the best round-ish blob you can, file it down ( edges or top ) so it's the 'correct' weight, crush it in a vice between good flat hard steel plates, while it is contained in a correct diameter hole drilled in a steel plate. But I haven't actually tried it yet ... maybe in the next week.
If you don't use the holed plate, you will get something pretty close, just with a rounded edge profile, and a dodgy circular shape. The plate will help both these features improve. But for the smallest 'nuggets' , maybe just weighing and squashing are enough ?

I'm thinking of making a couple of the replica nuggets from copper. Not because they will represent any real one, just for scientific comparisons.

On the subject of lead shot: Not being a huntin-shootin guy, I know nothing about # sizes etc, so I thought this Wiki guide was worth linking to, as it lists the diameter/weight of all the usual shots.
Notice that it also states: "The hardness of lead shot is controlled through adding variable amounts of tin, antimony and arsenic, forming alloys."
which makes me wonder about it's consistency, particularly with regard to conductivity, plus it would be really hard to actually measure the conductivity of a sample of shot.
https://en.wikipedia.org/wiki/Shot_%28pellet%29

You really like aluminium foil.
I question the use of it for a number of reasons. It's IACS value is typically 57%, nowhere near to the probable 10% - 30% figure for a nugget. The resulting 'dummy' is wafer-thin, so no use for testing edge-on, or anything other than dead flat on. And why the enthusiasm for folding the stuff up... just get thicker foil, surely ?

( I've just prepared a series of 0.10mm thick foil targets for testing, and a carefully cut length for conductivity measurements. It provisionally looks like 56% IACS, typical for 1000-series alloy, I'll get a good 4-wire measurement on it soon)

[Ferric Toes]

Munching through a few Ferrero Rocher chocolates yesterday, I wondered if a mimic 'gold' nugget could be made from the foil wrapping. Carefully removed and smoothed flat it is almost square at 9.5cm x 9cm and thickness 0.02mm. No reading was obtained on the Hocking conductivity meter for the single piece. Folded in half it read just 1.18. Progressively folded, I ended up with 64 layers and 11.2%. Further squeezing in an engineers vice brought the figure up to 30.5% which is very close to the Australian gold nugget.



For comparison another foil was screwed up and rolled into a ball, which was then compressed as far as possible in the vice. This more represents a nugget with inclusions, minute cavities and an irregular edge. In the last picture, the two measured ones are on the left, while basic folded ones on the right. Detection ranges are 9" for the 30.5% and 7" for the 11.2% using a Vallon with 7" round mono coil.

Eric.

[green]

Do I have any ideas? ....
The best one so far that's useable on lead and any solder type is to make the best round-ish blob you can, file it down ( edges or top ) so it's the 'correct' weight, crush it in a vice between good flat hard steel plates, while it is contained in a correct diameter hole drilled in a steel plate. But I haven't actually tried it yet ... maybe in the next week. Hope you have better luck removing the lead after smashing it in the hole than I did pouring it.
If you don't use the holed plate, you will get something pretty close, just with a rounded edge profile, and a dodgy circular shape. The plate will help both these features improve. But for the smallest 'nuggets' , maybe just weighing and squashing are enough ? Would you expect your smallest nugget simulation(1 to 2 grain gold nugget?) to look like mine if I followed your instructions? Would you use lead or solder? I have SN60 PB40 solder, do most or would we have to have to purchase a different solder?

I'm thinking of making a couple of the replica nuggets from copper. Not because they will represent any real one, just for scientific comparisons. I was thinking copper wire. Still think 19mm of AWG22,19 and16 make a good simulation target but wouldn't if not easy to obtain. Repeatable IACS and easy to make.

On the subject of lead shot: Not being a huntin-shootin guy, I know nothing about # sizes etc, so I thought this Wiki guide was worth linking to, as it lists the diameter/weight of all the usual shots.
Notice that it also states: "The hardness of lead shot is controlled through adding variable amounts of tin, antimony and arsenic, forming alloys."
which makes me wonder about it's consistency, particularly with regard to conductivity, plus it would be really hard to actually measure the conductivity of a sample of shot.
https://en.wikipedia.org/wiki/Shot_%28pellet%29

You really like aluminium foil.
I question the use of it for a number of reasons. It's IACS value is typically 57%, nowhere near to the probable 10% - 30% figure for a nugget. The resulting 'dummy' is wafer-thin, so no use for testing edge-on, or anything other than dead flat on. And why the enthusiasm for folding the stuff up... just get thicker foil, surely ? I'm guessing most would have regular or heavy duty aluminum foil in the kitchen. Cutting a larger size and folding to get a accurate 3.5mm square target is easier than shaping one for me. I'm thinking decay TC and amplitude need to be similar to a small nugget, maybe not flat and on edge since all nuggets wouldn't be the same.

( I've just prepared a series of 0.10mm thick foil targets for testing, and a carefully cut length for conductivity measurements. It provisionally looks like 56% IACS, typical for 1000-series alloy, I'll get a good 4-wire measurement on it soon)

Thanks for the input. Once we have decided on simulation targets, we still need someone or more to test for detection distance with a few detectors for referece to compare with the one we are making or repairing.

[Skippy]

It's the complete lack of consistency that I dislike about folded/scrunched/bent/etc targets. Perhaps if a squashing force in Newtons was specified ...

I do have some chocolate-wrapper foil in my collection, it fills in a gap between the cooking foil and the thinnest 'pie tray' foil. My thickest is 0.165mm. I was going to do a time-constant vs thickness experiment, which might show up the different 'foil grade' alloys used.

If it does look likely that a higher conductivity metal than lead-free solder or Eurocent Aluminium-bronze is called for, the most likely looking choice is pure zinc, at about 26% IACS. I'm not sure how easily obtained this is, though. It's used to make die-cast toys, but that's probably an alloy of zinc.
https://www.dynacast.co.uk/zinc-die-casting
Most high-purity zinc listed on eBay for laboratory use is thin, under 0.5mm, I did find some 0.8mm, for architectural/interior design use.
The zinc core of a US 1 Cent could be useable for smaller nugget replicas, it appears to be pure zinc, more investigation needed. Belgium and Germany had zinc coins in the early 1900's.
Example:
https://en.wikipedia.org/wiki/Belgia...f_World_War_II

[green]

http://www.geotech1.com/forums/attac...2&d=1546205793 Thinking TC might be alright, target area probably to large(amplitude higher than a small nugget would be).

Made some smaller targets folding foil. Started with 15x15mm square, cut in half(2 targets),folded one for square then folded twice for smaller square(3.75x3.75_8layers). Repeat with other half. Did the same for 14x14mm square and 13x13mm square.
Amplitudes might be closer to a small nugget. Harder to fold than the 2fold targets in nugget simulation_7. Thought the same targets might chart closer than they did.

[Carl-NC]

I don't understand the concern over metal type or purity. As I mentioned before, just about any metal can be used. If the goal is a set of targets that different people can replicate, then I think household aluminum foil is the best answer. You can create any tau you want by either surface area or layered thickness. You can adjust signal strength by arraying multiple identical pieces, just make sure they don't touch. If the thickness of household foil varies, then it can be measured and target sizes adjusted for proper tau. Probably won't amount to much.

[Skippy]

"I don't understand the concern over metal type or purity."
I was trying to make something that represented a real nugget. Something vaguely the same size and shape, so you could bury it for in-ground testing, tip it on edge to see how your detector responded. So targets that just mimic signal strength AND Tau are not necessarily ideal. Mr. Green has shown how lengths of heavy gauge copper wire will do this. But tip a round bit of wire on edge, and it's the same, because it's round. Likewise, something made of multiple bits of metal glued to a piece of plastic is not great.
And the 'concern' over metal type and purity is simply because lots of metals out there are rather unknown in composition. Lead shot isn't lead. If I buy some Eley shot here in the U.K, it could be noticeably different to the same shot made by BlackHills Co. in the US of A., and neither will be the same as pure lead.
We're not trying to be picky about the metal and its source. Look at the shortlist: lead, 60-40 solder, 99C lead-free solder, CuNi25 coin alloy, Zinc, EuroCent aluminium-bronze. All common, dirt-cheap, easily obtained.

And speaking of Zinc coins: Eric, do you have any zinc coins among your numismatic collection? Like the WW2-era German, Austrian coins ? I was curious what Mr.Hocking made of them.

[Ferric Toes]

It's the complete lack of consistency that I dislike about folded/scrunched/bent/etc targets.

I would suggest that there is a similar lack of consistency in nuggets? All these are different, in size, shape, source of origin, and quality of gold. Another variable is that reef gold is usually of lower purity than the nuggets it spawns. This might sound odd, but it is fully explained in the book 'Gold, History and Genesis of Deposits' by R. W. Boyle. Briefly, it is because the silver is leached out downstream in what is called placer gold, so that the further you find the nuggets from the reef the purer the gold is. The situation can be that 5 to 7% of silver is leached out of the surface layers, thereby purifying the gold, while the inner core retains the silver content and has a lower purity.

Perhaps if a squashing force in Newtons was specified ...

I just tightened the vice until I got a sensible IACS%

I will check out the zinc and post the result.

Eric.

[geoscash1]

It's the complete lack of consistency that I dislike about folded/scrunched/bent/etc targets.

I would suggest that there is a similar lack of consistency in nuggets? All these are different, in size, shape, source of origin, and quality of gold.

I agree completely with this. Maybe Im misunderstanding some of this thread.

I have a few nuggets I use for my testing. For example, using one of my detectors, 1 nugget will change its detection depending on how it is held. One side of it, the detector detects it at 4 inches but turn it over and its only detected at 2 inches, turn it on its edge and it detects less than 1 inch. Same goes with whatever detector used or nugget used.

Ferric toes, Do you or any of you other guys use any real nuggets at all for any of the tests you do?

Just curious to this subject as that is my primary source for detecting..

[Skippy]

I was under the impression it was the lack of consistency of real nuggets that was the entire problem. It makes comparisons and related tests inconsistent.
If Brian Bryant says: "I can detect a 5 grain nugget at 20cm", and Charlie Charles says: "I can detect a 5 grain nugget at 20cm", are their detectors the same? Probably not, if they swapped nuggets with each other, it would give more useful info. But poor Andy Andrews doesn't even have a nugget yet to test his machine with. ( names have been changed to protect their anonymity )....

You can get a lot of clamping force from a bench vice. I was doing some car repair a few years ago, inserting four wheel-fixing studs into a hub carrier. Not easy, I had an extension pipe on the vice tommy-bar. I later calculated 20 tons force (20000 kg-force, 200000 Newtons).

I'm going to sand down a US 1 cent to see how the zinc core responds.