Quest For Nasa Tom and others On F75 and Coke

After Using Minelab Multi frequency detectors for quite a few Years now, i wandered what your thoughts and findings are Tom on Why detectors like the F75 and slightly lesser T2 Find naturaly occuring Coke and or Endustrial Coke from Iron smelting in our fileds over hear in the uk.Also Magnatite and other Hot rocks too.

I rarely found any coke at all with the The explorers and or the Etrac and still wander why Coke is nearly allways picked up with my F75.I can deal with coke in most cases and recognise the tonal responses, but it does trick me at times.

Please accept my applogies if there are other topics posted of this nature.
Keith
Whiggy.



Edited 1 time(s). Last edit at 12/04/2013 05:22PM by whigsvolt.

In general, single freq units have a bit more of a difficult time with coke. . . . . especially the newer generation of 'overdrive' units with DD coils. Changing Grnd Balance settings can make a bit of a difference........ if your dirt conditions allow. Multi-freq units comp them out better........ but......... with the tradeoff that..... multi-freq units are less sensitive to lower (relic) conductors.

Ask this question on a UK forum, and all the Minelab supporters will smugly tell you they never dig coke, it seems to be one of the good features of BBS/FBS, though I can't help wondering if there's a catch, such as coke-masking still occurs...
As to why single-freq machines pick it up, it's something to do with graphite's magnetic properties. I know detectors also pick up graphite rods from electric carbon arc lamps really well, too (I've found a couple, myself). There are 'magnetic levitation' experiments you can perform (kits available online), using diamagnetic materials, the main two choices (due to their relatively strong diamagnetic response) are bismuth and 'pyrolitic graphite'. This is a specially processed thin sheet of graphite, but it's not implausible that some portion of a lump of random graphite / coke is also magnetically responsive.
High freq machines are worse, you will notice that target ID's for the coke are normally in the 16 to 25 range, indicating 'best-detected frequency' of 25KHz plus.

Pyrolytic graphite levitation:
[scitoys.com]
[www.amazon.com]



Edited 2 time(s). Last edit at 12/04/2013 08:57PM by Pimento.

I've been hankering for a good hot rock discussion. Aren't the little round balls that you find along railroad tracks coke? We call them pig irons and they make great sling shot ammo.
About the hot rocks. My T2 loves them. I never knew how bad the hot rocks were around here before I got the T2. I've learned to use this to my advantage. The rocks I am talking about are lightweight grey colored and usually about one inch across. They usually hit low in the single digits, but often try to make me believe they are coins. They will ID high and deep, but they are just under the surface. What are these rocks? If some detectors do not pick up on them then are they masking good targets? I believe they are. Do any detectors have the ability to see through hot rocks? I have my theories, but I'm sure some of you guys know alot more than I do.

[en.wikipedia.org]) try to avoid the areas I hunt that have coal/coke in the soil. All I can do is what Tom suggested! "1) Adjust Grnd Bal to completely 'null' (no audio response) to the majority of hot rocks.

or

2) Adjust Grnd Bal whereby the audio response to hot rocks is highly identifiable/differentiable from 'real' metal targets. Some people call this a 'boing' audio response. In any case.... it is a 'smeared' elongated (not sharp audio) response.

The latter option allows for you to have the Grnd Bal adjustment being closer to also include compensating for bad dirt/mineralization. " I have never burned coal in a stove before guess byproduct would be coke? Bet there is a lot out there! HH P.S. the 2 short fluffy sentence's at the front-end & back-end are mine the substance in the middle is a copy-n-paste from Tom{$ }thanks Tom!



Edited 3 time(s). Last edit at 12/05/2013 02:40PM by rapidroy7.

We have some sights around the city hubs here were they used Coal Furnaces...you can tell when you get to the spot's in the yard where they threw away the burnt coal when the furnaces were cleaned out....its awfull to hunt around.. machine goes crazy..

I remember hunting one of those spots one time with a Bandido and balanced to the coal and found a Seated liberty quarter in all the noise...only machine I had at the time I could get to hunt in the stuff...Years later went back with the first model Musketeer and pulled an Barber half out of the coals with ease.. then a 1832 Largie in awesome shape....so if you can hunt those spots they hold some nice stuff....but I notice I cant get low conductors out of the stuff just high coductor's even when using the sovereign...I just got High conductors out of it...Buckles and coins and high reading Buttons like Cast I's...

Lickily the spots I hunt mostly are rural and no coal...

But balancing to it seemed to help on the bandido..

Never tried the T2/F75 in the stuff so not sure but would think the I.D might help some if you cant bal to it..
The GMP has a setting on the disc for it...it must read right below foil or some where close...maybe right between iron and foil...probably were the good stuff comes up in English site..like small hammered coins and scuh...
Keith

Thanks for the feedback so far.
The problem we have here in Scotland is that we have tons of scattered naturally occurring geological coke as well as the industrial coke.
I have always thought that there was some kind of masking in the MF mine labs but as Tom says it must be something to do with the way the coke is processed/computed.
I can certainly live with this on the F75 and can avoid around 50% of it under the coil, and most of the small pieces are right on the surface anyhow.
Keith.

I just performed some extenisve testing with coke today. In a nutshell:

F75: Could not Grnd Bal out the coke. Also could not Disc out the coke. But.......... two things.
1. Grnd Bal would moderately affect the way coke would report. And with proper (coke) Grnd Balance settings....... the coke would audibly (slightly) "smear". . . . making it 'fairly' easy to differentiate from 'solid' metallic objects/targets. A slow/tedious process....... but do'able to a tuned/astute ear.
2. On the F75 platform..... this particular type of coke will ID the full span of conductive target ID........ from foil to silver quarter........ on each/every piece of coke...... making Disc impossible. However......... rotating your body around the coke (whilst sweeping coil)...... and the coke will 'ID' span from 18 - 86 on the F75. NEVER locking on to a small/narrow ID bandwidth ....... (((thusly.... a good clue it's coke))).

CZ: ALL of the exact same coke will continuously/constantly/consistently/repeatably ID as 'foil'. To be exact........... it'll ID on the very high end of the 'foil' range (almost into nickel). If you are running a CZ-3D....... 'foil' has (deliberately) a special/unique single tone assigned to 'foil' (a medium-low tone)...... making ID of coke extremely reliable/accurate...... simply by the audio report; subsequently...... preventing you from having to have your eyes glued to any ID meter. HOWEVER............ the down-side is........... you must circumvent digging/recovering any/all 'foil' targets. MANY relics ID as 'foil'.

XP GMP testing soon to commence.

I think one of the main problems with coke is how variable it is. It obviously comes in different shapes and sizes, and it's tempting to say that larger pieces give a higher ID value, they certainly seem to give a stronger signal. But the chemical composition is equally important - how burnt, what quality coal it was when originally mined etc etc. I've had pieces read in the 30's on an F75, and they were rather small, 20mm/ 0.75", but large pieces, 3 inches can read in the low 20's. They do tend to have a fuzzy indistinct sound, particularly the larger samples, I imagine this is due to them appearing as multiple targets, rather than one solid piece. I couldn't describe the effects of coke-masking, too many variables. One of its redeeming features is it's weak response means you rarely dig it from more than 3 inches down.

XP GMP = I just finished extensive testing of the GMP and coke. In a nutshell...... failure. From dime-sized to golf ball size pieces.......... the GMP reported a solid mid-tone to deep depths. Changing Grnd Bal altered nothing. Placing Disc on max setting...... and the coke still remained a very strong signal. Burying a dime 1" below a piece of coke........... and the dime is fully masked.

Taking a piece of coke about half the size of a golf ball........ placing it in a zip-loc bag.......... then hitting it with a hammer so as to 'powder' the coke. Now........ take this coke powder and sprinkle on top of a 4" deep dime (in a test-garden)........... and the dime is completely undetectable.

Yes......... there are different/varying types of coke........ and of varying strengths. Specifically 'relic' hunting a field that has a fair amount of coke is virtually impossible........ as coke and 'relics' produce the identical audio (mid-tone) response.

Now........ as far as adjacent target separation, , , the GMP still retains flagship status. Bringing a high-conductive coin (clad dime in this case) closer and closer to a half-dollar-sized piece of coke............ to the point where the dime is touching the coke (to include: partially under the coke)...... and the GMP still retains extremely enhanced adjacent target separation characteristics (flagship status)....... by reporting a high-tone for the dime...... and a mid-tone for the coke.

As discussed before....... Some fields can be covered with this light weight coke/shale/cinders all turned up to the serface after the plough. Have said for years the fields became dead especially when wet. Pleased someone has proved the masking ability of this menace, and the inability to recognise before digging.
Having the Goldy explorer and T2 since they come out, out of the three the Explorer found the most in these conditions, don't know why, any finds are always very shallow not more that 2/3 inches.
Malcolm

Natural coke is formed when a coal seam is intersected by a volcanic intrusion...from the about link under this video@[www.youtube.com] P.S>makes a great heat shield just ask NASA! stock-up?



Edited 1 time(s). Last edit at 12/06/2013 06:22PM by rapidroy7.

PittsburghWill --

The little round balls you speak of are, I think, iron ore. If they are reddish-colored, they are iron ore. There are also "nuggets" of silvery metal, which I think are "pig iron nuggets" in the area, that I dig up alot when hunting back home in PA, as they sound pretty good. Not sure if these are the ones you refer to by the railroad tracks, or if it's the reddish ones (iron ore). They (the silvery pig iron nuggets) are often mixed in with gravel and what I think is slag, on some of the gravel roads in western PA. But, coke is still something different -- it is a product formed by burning off the impurities of coal, and is used as a fuel in blast furnaces...and I think some folks (as has been mentioned here) call "coke" just the after-product of burning coal (in a fireplace or furnace).

Steve



Edited 1 time(s). Last edit at 12/07/2013 02:31AM by steveg.

I think in England the Coke they refer to is from the turn of the century farm tractor's...they were coal powered and the burnt coal,, must of fell around the fields as they plowed/harvested...

I seem to remember that the GMP could handle THAT COKE with the coke setting clicked on...From reading about it...

Watch this guys GMP video...it rejects coke when it's in the Auto setting for coke....Gives iron tone for it.

[www.youtube.com]

I think Norfolk wolf was impressed with the GMP'S ability to reject coke..

Keith



Edited 1 time(s). Last edit at 12/07/2013 01:43AM by Keith Southern.

Some excellent feedback and testing info their.
Many thanks.

Yes Steve. The ones I spoke of are the reddish balls. You can find huge piles of them around old rairoad tracks around here. What does coke look like? The "hot rocks" that I find all around here do ID like the coke that Nasa Tom described above. They will hit like a coin at one angle and drop out at other angles. These rocks are everywhere and I can't help but think that they are masking a whole lot of good finds. I wish it wasn't freezing outside.

Tom it so seems when you tested the GMP you did not click the auto coke setting on or did you? it sound's like you were using the disc at max which would still give it a mid tone since it runs out of range....the auto setting for coke will advance the disc further...probably above foil..Then will give the coke an iron grunt..

You may have done this but in your wording I notice you said maximum disc..and as we Know maximum disc is still below foil... the Auto setting is at foil or a little higher...

I know all the resolution for iron unmsking is gone but it does allow for open filed type hunt's in auto if COKE is abundant..

just wanted to check and see what if you invoked the Auto setting..

Keith

Good catch Keith........... and I even have it written in my notes to report; yet, did not.

Clicking the Disc in 'auto' and the coke reports as iron/low-tone............ but only for the first 60% - 70% of depth range. Any coke beyond 70% of the GMP's detectable range........... and again............. it ID's as mid-tone. And any coke that is in that 60% - 70% of maximum detectable range.... gives a low-tone/mid-tone warble.......... prompting the operator/detectorist to 'dig'............ as it sounds exactly like a non-ferrous target in extreme close (co-locate) proximity to a ferrous target.

In any regard........... even with GMP in 'auto' Disc............. all 'masking' rules still apply with coke.

PittsburghWill -- those are iron ore pellets. My dad got me some when I was a kid, from the mill...for use as -- just like you said -- slingshot ammo!

Don't know about the "hot rocks" you are referring to, but I wonder if it's not "slag..." Slag is a by-product of steel production...it's what gets "separated" from the iron during the combustion process...it is the "impurities" in the ore, which separates out...they get rid of the slag, and keep the purified ore -- I think this "purified ore" is the "pig iron," and the "slag" ends up as porous chunks of "rock." Slag was used as "gravel" for gravel roads...and sometimes has "pig iron" in with it. I am wondering if some of the "hot rocks" are not slag...

Here are some pictures of "slag..."

[www.google.com]

Steve



Edited 1 time(s). Last edit at 12/07/2013 02:56AM by steveg.

OK Tom Sounds Good on the testing...I figured you had..

I think I see why on the English fields when there plowed yearly they like to use the auto setting....and why they like to use about half sens.....they probabbly counter act the deep Coke from going mid tone with less sens and mainly look for surface finds.....

Its got to be a nightmare to be on a 2000 year old Roman site and have 100 year old coke messing with your hunt!!!!

Keith

I'm trying to post a pic from photobucket. Never done this before, so forgive me if I screw it up. This is a handful of rocks that I dug on my last hunt. They are all the same material. Very lightweight.

Will, when you break those stones, are they shiny black, like coal? I always come across 'hot rocks' or 'cold rocks' (not sure the difference) that most often give a mid tone on my f-75 in 4 tone. In 4h, the bigger ones ring high tone....they are shiny black under the dirt coating. They also set off the pinpointer. They are always around the old home sites and occasionally in the farm fields, here in SE PA.

When I was doing hot roof's in the 1970's we would put 'slag' over the asphalt as a protect from the sun and weather. It looks like those in the pictures that Steveg posted...hard and brittle with little varying size holes.

There is a old one room school property where these 'slag' are under the topsoil...makes the 75 erratic and I can't get past them. I only found a few wheats and merc dimes on top of the slag...nothing past the slag where the oldies are hiding.

Ozzie. They sound like the same rocks. I find them everywhere. I guess everywhere I hunt is old home and farm sites. There was also alot of coal mining in my area back in the old days. Have you used a small coil at that old school site? I was using the 5" coil on my T2 the day I dug those rocks above and I also pulled out a 1902 barber dime and 1859 indian head. I think the small coil is key in hunting rock infested sites just as it is in trash.

Keith........... Got it in one.
Malcolm

Will, that site is on my list to hunt with the 5" and my new 75se. I can't remember if I hit it with the old 75......I'll keep you posted.