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18K White Gold becomes magnetic when filed or cut in half

January 9, 2010

Hello, My name is Joseph Werner I am a franchise owner of a gold buyer, and a Graduate Gemologist.

My question is this. I was brought 12 bangles that were hallmarked 18K. I used a magnet and there was absolutely no magnetism or pull on any of the bangles. I then acid tested and the item passed the stone scratch test. I then Filed into the item to check if solid. Again no unusual reaction to the test acid. HOWEVER once the bangles had been Filed, and/or cut with wire cutters they became EXTREMELY magnetic.

If anyone has experienced something such as this please respond.

Is there some sort of plating that will stop the ferrous magnetic reaction?

Thank You Kindly for your time.

Joseph Werner
Precious Metal / Gem Dealer - Miami, FL USA
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January 11, 2010

Hi, Joseph. To my knowledge there is no way to block magnetic attraction.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


January 13, 2010

Thank you for responding, Do you, or does anyone have any knowledge of a way to "de-magnetize" ferrous alloys?

Is there some way to "de-magnetize" and the item in question can be "re-magnetized" after so sort of interaction with a magnetic alloy( example; steel wire cutters/steel gold files, etc..)

Thanks, I appreciate your response. I am perplexed, as is every Goldsmith/Gemologist/and Plating Expert I have spoken with.

Joseph Werner
- Miami, FL USA


January 13, 2010

Hi. I think the next step is to find out what these items are made of. Someone with spectrographic analysis or x-ray fluorescence equipment could probably answer that question for you.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

January 14, 2010

18K gold is basically 75% gold by weight, with other metals taking up the remaining 25%. These metals can vary, depending on what colour you are seeking. The most common "other metals" are copper, nickel, palladium or silver, but some of the more esoteric coloured gold, such as blue gold, can contain up to 25% iron. The most common magnetic metals used in gold alloys are iron and nickel, both of which will give evidence of magnetism to the alloy.
It is also possible that you have an artifact that is a magnetic base metal that has been plated with 18K gold, so as Ted says, you need to find out exactly what you do have in your bangle and how homogenous it is with regard to 18K gold - if it is plated 18K gold, it will only have a surface layer of gold on it.
My next question is why do you want to demagnetise it? If it is 25% Fe, it will be magnetic by design. It is possible to make iron non-magnetic, as with many stainless steels, but it will reduce the gold karats used in your bangles. One way to demagnetise a magnetic material is to heat it up, but unfortunately iron alloys are inherently magnetic, so even if you do succeed in demagnetising your gold, it will only return on exposure to another magnetic field.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


First of two simultaneous responses -- January 14, 2010

I know all of the above, except about the heating of iron to remove magnetism. I Do not want to remove the magnetism. I was wondering if someone out there was making magnetic metallic jewelry and marking it as real gold, and then trying to pass it off as white gold......

Anyhow..... Its not really worth my time/effort/cost off analysis to find out exactly what is in there. To me it is worthless as even 10K white gold mixed with nickel has no magnetic properties. I have worked with gold for a very long time. never seen anything like this.

It was just so odd I needed to see if anyone had ever seen anything like this before. Thanks!

Joseph Werner
- Miami, Florida, USA


Second of two simultaneous responses -- January 14, 2010

If it wasn't attracted to a magnet before cutting or filing, and it was after, then you've got something that becomes ferromagnetic with cold work. The only metal I know that does that is 300 series stainless steel, also known as 18-8 stainless. The cold working causes a transformation from an austenitic arrangement of the atoms to a martensitic arrangement, and with that transformation comes ferromagnetism.

Lee Gearhart
metallurgist
East Aurora, New York



January 31, 2010

I Bhupesh Mulik, gold refining officer suggest that first you test this sample for iron content using x-ray fluoroescence method. You will get the percentage of iron within 25% of alloy which mix in pure gold of your eighteen kt white gold. There is a chance of magnetism for cobalt based alloy also.

Bhupesh Mulik
- Mumbai, India


February 7, 2010

Even a small percentage of Co (<1%) can make gold magnetic when exposed to strong magnetic fields for some time, though I am not sure if temperature has any role to play.

H.R. Prabhakara
- Bangalore, Karnataka, India

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