Why is my restaurant silverware magnetized?

Question

Why is my restaurant silverware magnetized? Specifically, if I lay all three flat on the table, and touch the bottoms of the handles together, I can pull the knife with the handle of the spoon.

I have a video (if I can figure out how to upload it from my phone).

I think that you would have to link the video here via some website like Youtube. — noir1993, Mar 23 '14 at 21:13

score 14 · Accepted Answer · edited Jun 04 '20 at 16:03

First off, restaurant silverware is typically not made of silver, but rather of steel or stainless steel. A common steel used in cutlery is 18/10 stainless, which has an austenitic crystal structure. Austenitic steel is normally nonmagnetic, which is why most stainless steel objects are not attracted to magnets.

However, as mentioned on this surprisingly interesting website devoted to steel fastener manufacture:

There are five classes of stainless steel (ferritic, austenitic, martensitic, duplex, and precipitate-hardened) and only one is nonmagnetic (austenitic).

The microstructure of austenitic stainless steel can be changed by a process called martensitic stress induced transformation (MSIT). This is a microstructural change from austenite to martensite and the transformation can occur due to cold working (the process by which many fasteners are made) as well as slow cooling from austenitizing temperatures.

I am not experienced in the methods used in the manufacture of cutlery, but if there is any cold-working used in the shaping of the 18/10 stainless cutlery, martensitic stress-induced transformation might be the culprit behind the ferromagnetism.

Add that to the magnets Enucatl mentions which are sometimes used by restaurants to pick up the cutlery and the hysteresis property of ferromagnetic materials, and you have a possible explanation for why two pieces of stainless cutlery seem to be magnetized and can attract each other.

Electromagnets are a handy way to move steel around, so there's a good bet the silverware got magnetized during manufacture. — Mark, Mar 24 '14 at 04:54
But what if the utensils *were made of silver*? Is silver not magnetic at all? — 40XUserNotFound, Mar 24 '14 at 07:16
Due to the increase of induction cooking ranges, many pot manufacturers are moving to using magnetic steels. If the same company is producing pots and cutlery, they might also switch the type of steel in the cutlery for economic reasons. (Note that I have no proof that this is happening, it is just a hypothesis). — rumtscho, Mar 24 '14 at 11:56
@Cupcake: Silver is diamagnetic, not ferromagnetic, so there won't be any noticeable effect. — DumpsterDoofus, Mar 24 '14 at 13:46

score 11 · Answer 2 · edited Mar 24 '14 at 16:51

11

They use magnets to pick up the silverware so that it's not thrown away with the leftovers.

edited Mar 24 '14 at 16:51

Emilio Pisanty

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answered Mar 23 '14 at 20:36

Enucatl

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I also heard they might heat the silverware through induction in the dish washer, which magnetizes it. Don't know if that is true, though. – jdm Mar 23 '14 at 21:02
I doubt this - to reliably separate separate silverware and waste, it would have to be a pretty powerful (and dangerous) magnet. – Kvothe Mar 23 '14 at 21:44
2

They're real, @Kvothe: http://www.google.com/search?q=magnet+flatware+catcher – jscs Mar 23 '14 at 21:49
I stand corrected :) – Kvothe Mar 23 '14 at 21:51
I used to work in a major restaurant (Chili's) and we never used that. – Engineer2021 Mar 24 '14 at 15:47

score 0 · Answer 3 · answered Mar 24 '14 at 11:34

Where is the cutlery stored? Is it near one of the building piles? That could have been magnetized when the restaurant was built and they could be inducing the magnetism into your silverware.

I've experienced this before - I've had CRT TVs and monitors that could not be adjusted because the magnetism from the pile was affecting them so much. The CRTs were about 1 ft away from the pile.

Why is my restaurant silverware magnetized?

3 Answers3