Is Ceramic Tableware Detectable?

[GB_Amateur]

(Long article.  If you think you'll get bored of the background info and stop in the middle, skip to the Testing section to see what a metal detector has to say.)

Introduction

Detectorists occasionally come across ceramic tableware/dinnerware at sites.  For example, I found some in a ~1880's Colorado ghost town.  A friend of mine found a piece (which I was able to identify and date to the 1890's) near a high altitude Colorado miner's cabin associated with a small silver mine.  Western USA explorers/settlers/miners may seem backwards and uncivilized (and that is true in some cases) but often they longed for the finer things of the lives they left behind.  Ceramic dinnerware was both utilitarian and aesthetic.  Coin&relic detectorists around the world use pottery and other ceramic pieces, often found on the surface, to indicate good places to detect.

In a previous life 😁 (actually 1998-2015) I was a avid (make that obsessed) collector of dinnerware by a particular USA manufacturer, accumulating a collection of 2000 pieces by scouring antique malls/shops but also occasionally other sources like rummage sales and Ebay.  Not surprisingly I did a lot of research on the subject during my collecting years.  Here are some results relevant to metal detecting.

Plausibility

In this first photo are two 6" diameter plates, both with filigree decoration and an edge line.  The lower decoration is gold and the upper one is platinum (often mistakenly but understandably called 'silver').  The upper piece was manufacture in 1937 and the lower (gold) one in 1952.  Each sold (usually as part of a set) for considerably less than $1 -- let's use $0.20 as a reasonable amount.  Can we possibly reconcile these two 'facts' -- precious metals on inexpensive items?

It is known that gold can be worked into very thin sheets.  According to Wikipedia, typical gold gilding is 100 nm thick.  ('nm' is the abbreviation for nanometer.  There are a billion nm in a meter.)  Scientists in the laboratory have done ~200 times better -- less than 0.5 nm which is actually about 2 gold atoms in thickness!  Coatings on precision mirrors (e.g. astronomical instruments) are also about 100 nm in thickness -- same as fine gilding -- and that is thick enough to reflect in the high 90% decade at infrared wavelengths.

About 15 years ago I took a tour of the Homer Laughlin China factory in Newell, West Virginia -- located in the very tip of that spike in West Virginia's NW part, along the Ohio River across from East Liverpool, Ohio and about 45 miles WNW of Pittsburgh, Pennsylvania.  They actually took us to the factory floor and one of the things they showed us was a technician/artist painting the gold edge line on a piece.  The claim was that it was pure gold (24 kt) but my research indicates it was more likely 22 kt.

I calculated the approximate amount of gold on the edge line of the lower plate in the picture above and at today's price ($58.54/g) it comes out to about $0.06 worth.  However, when that piece was made, gold was $35/oz (a factor of ~1/60 compared to today) so that material cost would have been more like $0.001 (at tenth of one cent) for a 6" plate.  That certainly seems plausible, even if the thickness was several times that 100 nm assumption.

Testing

I used the Minelab Equinox 800 with 11" coil, Park 1 mode, gain of 24 in 10 kHz, 15, kHz, and 20 kHz modes (MultiFrequency too noisy with EMI) to see if the following soup bowl would give a signal.

This is a rather extreme example in terms of the amount of platinum for an inexpensive piece of dinnerware to contain.  The platinum band is 1/2 inch wide (1.27 cm) and the total calculated mass is about 0.011 g (assuming 100 nm thickness of pure platinum, so adjust accordingly).  At today's price of $36.49 g those assumptions translate to $0.40 worth of platinum in this dish (I don't know the platinum spot price when it was manufactured in 1932).

The digital Equinox's TID waffled between 1 and 2 and the signal strength was maximized when the coil was centered over the dish, with the coil about 1 inch above the platinum band, resulting in 3 arrows out of 5 ("depth meter" reading).  Sweeping over the entire dish also gave a weak hit when the edge of the coil crossed the edge of the band.  I also tested a similar sized dish which had just an edge line and filligree decoration similar to those shown in the first photo.  There was no noticeable response by the detector on that one.

[Gerry in Idaho]

Dang good work and write up Chuck.  Your math is quite above standard as well as your collection...provided the math is correct.  But I'm not hear to put doubt on that.

I could easily see the thicker band of gilding earning a response from the NOX, especially in Gold 1 Mode, ALL METAL, Tracking OFF.  Your testing in all lower frequencies and getting a response was interesting, but I do like the #1 and #2 readings as I find many nuggets at the #1.

I don't think you have enough there on your 2000 pieces to make it worth scaping at this time.  I also wonder (as your post asked) if certain ceramic does have some metals or lean in the glasses of the shine.  Here is why I say this.

Valens Legacy (Caleb) emailed me and asked if marbles had metal in them because he dug up some with this Equinox.  I thought it was random luck, as I too have found a few marbles in the same hole as I dig a metal target.  Well he did some testing and sure enough, the marbles do respond.  So he educated me and we both think there must be some lead in the glass.

Anyway, I hope someone else gets to take the Holiday dishes out of the China Cabinet and see if their NOX can detect them. 

Interesting read either way.

 

 

[GB_Amateur]

14 hours ago, Gerry in Idaho said:

Your math is quite above standard as well as your collection...provided the math is correct.

Well, in order to know if my math is correct someone (besides me, since I already have) needs to go to the trouble of redoing it.    Interestingly the first time through it I made a mistake.  "Measure twice; cut once."  (Err, maybe that's not what this means....)

14 hours ago, Gerry in Idaho said:

Well he did some testing and sure enough, the marbles do respond.  So he educated me and we both think there must be some lead in the glass.

Hmmm.  Lead glass isn't free lead but rather its oxide compound.  However, as many prospectors know there are some compounds that are actually conductive (although not many).  Coincidentally I just read an ICMJ article by Chris Ralph where he talks about the mineral Cuprite giving a strong response to a detector, and that is a copper oxide (Cu2O).  (But, minerals we find aren't always as pure as the pristine specimens pictured in rock handbooks and on Wikipedia.  So I don't know if it's the copper oxide or some kind of contaminant.  Someone here probably does, though.) 

Somewhere around home we have a (heavy!) leaded crystal pitcher, which we can't use because supposedly the lead can leach out and contaminate the liquid in it.  If I can find it I'll swing a detector over it.  That should answer one question, but not necessarily Valen's.  If 'yes' it will keep your hyphothesis alive for at least another day.

[GB_Amateur]

I performed some followup investigation instigated by what I considered a serendipitous finding -- the geometrical response to the ring-pattern of the dish.  Here are a couple more photos and then I'll explain:

 

The first photo shows both the dish with platinum decoration and a piece of aluminum of similar size & shape to that dish's inner metallic ring.  The aluminum is 1/16 in (1.6 mm) thick, 5.95" OD, 5.17" ID, and weighs 18.4 g.  I weighed a 12 oz aluminum soft drink can (with pulltab still attached 😁) at 13.5 g. so this aluminum ring is about 1 1/3 times as heavy.  (More comparisons, but with detector, later.)

The seond photo shows the aluminum ring placed inside the dish and oculting most of the internal platinum decoration.  (I mentioned in the previous post that the platinum ring's width was right at 0.5 inch = 12.7 mm.  Compare that to the ~0.4" width of the alunium band.)  Also shown is a 3" x 6" food container bag.  I couldn't get a resistance reading on any surface (apparently coated with a non-conductor) but I think it contains a very thin layer of evaporated aluminum.  This one is from a cookie tin -- inner liner to seal out moisture.  Most park and school detectorists have found similar items as they are in fairly common use, including some potato chip bags, etc.  This one as tested has between 2 and 4 layers -- both sides of the bag (that's 2) and for about 1/3 of it there was an additional folded over seam so add another 2.

Here are some air test comparisons made with the Minelab Equinox 800 and 11" coil, Park 1, gain=24, 10 kHz operating frequency:

Platinum ring in dish:  TID of 1-2, max detection height (centered on ring) approximately 6 inches.

Aluminum(?) coated food bag, detector swung across in the short dimension direction:  TID of 1-2 and max detectable height ~6 in.

Aluminum ring:  TID of ~37, max detection height (centered) approximately 20 inches.

Aluminum soft drink can (placed on side and then flattened):  TID of 23-24 and max detection distance ~20 inches.

I also tested the alunimum ring and soft drink can in Gold 1 mode @40 kHz , gain=24.  TID's were ~33 and ~23 respectively and I was able to get the coil another 4 inches away (compared to Park 1) for both targets.

Summary of detection tests:  the platinum decorated dish and the aluminum(?) coated food bag gave similar TID's and similar max detection distances.  The aluminum ring and the aluminum drink can showed similar max detection distances (when detector was set up in the same manner) but the ring gave a much higher digital TID reading than the can, in both Park 1 @10 kHz and Gold 1 @40 kHz.

Thought experiment: 

1) start with a coin (e.g. USA 25 cent) and perform an air test from a fixed distance (let's say 6").

2) cut the coin in 3 equal pieces and place them on a virtual (12 hour) clock face whose diameter is the size of the detector's coil (11" in my case) with the coins around the edge at 12 o'clock, 4 o'clock, and 8 o'clock.  With coil 6" above this plane swing your detector from various directions.

(Note: either ignore the fact that the shape of the pieces changes from step to step or if you insist, melt them and recast in disks.)

3) cut each of the 3 coin pieces in half (so now 6 equal pieces) and place them similarly at 12, 2, 4, 6, 8, 10 o'clock.  Repeat the detecting tests as in step #2.

4) cut the 6 pieces in half (resulting in a total of 12) and place at each hour location around the rim of the virtual clock.  Again investigate with the detector from many directions, coil being 6" above the target plane.

5) and higher steps, continue dividing up the pieces and placing uniformly distanced around that 11" diameter circle.

Will the detector's signal strength change as you go from step to step?  Where will the max signal strength occur for each configuration?  (Think of the aluminum ring in the real air tests above as made up of many small, equally uniformly distributed individual pieces.  Recall my calculation in the earlier post that the total mass/weight of the platinum in the dish was 0.011 grams which is 1/6 of a grain, and I detected it, admittedly in air, from 6 inches away.  I definitely made an assumption about the thickness of the platinum layer, but also recall the manufacturer had to keep that low in order to make a profit!)

Is all this just an academic exercise or is what we learn applicable to detecting?  Have you ever located a signal, dug to find nothing there, but subsequently discover that there were two targets (one on each side of the signal location) separated by the coil diameter?  Whose to say you'll never get three targets located (approximately) around a circle about the diameter of your coil?  And why stop with three?  (Note that the diameter of the circle that the targets fall on can be different than the coil diameter and still lead to similar results.)

Step 1 of the thought experiment is what we typically think of when we detect -- that is, an isolated target.  The higher steps (without the strict uniformity) are what often occurs in trashy sites, and from my experience those are the places that (still) have desirable targets.

 

 

[GB_Amateur]

17 hours ago, Gerry in Idaho said:

I could easily see the thicker band of gilding earning a response from the NOX, especially in Gold 1 Mode, ALL METAL, Tracking OFF.

What about a GPZ?  I really thought someone would respond/post that this actually happened when searching for gold around old miner's cabins, but then realized very few gold detectorists (especially with high powered PI's and ZVT's) do that.  Thick trash around the cabin isn't worth the hassle when there are open fields, mine tailings, etc. all about with much less trash to mask or masquerade as a nugget.

[EL NINO77]

GB_Amateur..you have done a very nice test which shows that even a very thin but sufficiently large and wide layer of metal can be very well detectable by a metal detector. which has generally excellent inductive properties ..👍

.... It would be interesting if you tried to use equinox at different frequencies ... where it would show what detection force and range a certain 1F frequency has on Equinox ..

As for the test on lead glass - "bohemia crystal" ... so in general, about 23_25% lead was used in the production of such glass .. and I have enough of this type of glass at home .. so I can do some specific tests ..