Inquiry about "sintered" coins?

[RWB]

Just for fun...

 

A poster who shall remain anonymous on a board that shall remain nameless, asked a question that shall remain useless, to wit: "I need some help on a diagnostics of a sintered coin. [sic]"

 

No U.S. coins were ever produced on purpose or by accident using sintering technology.

 

[physics-fan3.14]

Was he perhaps asking about how to identify a counterfeit coin produced by sintering? Or perhaps how to identify jewelry pieces?

 

Or is there another application of sintering that I'm not aware of?

 

Has any official mint ever used sintering to produce legitimate coins?

[CaptHenway]

I am aware of sintered medals but not sintered coins. I question whether they could be made by that process economically enough.

[dadams]

Improperly Annealed Planchet ?

 

Annealing - The heating (and cooling) of a die or planchet to soften the metal before preparation of the die or striking of the coin.

 

"A planchet may also pick up a coating if it is improperly annealed. This is a somewhat common error but one that is very difficult to authenticate. Improper annealing is often confused with toning coins. Unfortunately, improperly annealed planchets can take on a variety of colors from black to copper red. They are caused by over heating the planchets."

 

[Conder101]

The explanation they used to have for a "sintered planchet" error was that copper dust from a previous annealing of cent planchets settled on a subsequent annealing of another denomination and being fused to the surface of the other coins. Copper dust sintered to say a five cent piece.

[RWB]

I suspect that refers to what is commonly called "fire scale" - copper oxide. Most oxide contamination was eliminated in about 1901 with the mint's transition to rotary gas annealing furnaces.

 

The only reason to use sintering (with powdered metal) would be to form something out of material that is difficult to melt such as tungsten....or a politician's ego.

[Conder101]

Yes that is what it is, but I do believe that is what they are talking about when people speak of "sintered planchet" errors. That, or simply oxide layers that don't get cleaned off of planchets after annealing.

 

In other words discussions of "sintered coins" are simply misdescriptions.

[messydesk]

The "sintered planchet" term was widely used when the President dollars first came out and people would find a brownish coin in a fresh, BU roll now and then. In order to sell it for Obscene Profit™, you had to have something to call it.

[RWB]

Then call it "brown stain" or "oxide scale" or "bathroom scale?" ... don't misuse words just because they sound "technical" or "authoritative." This is just as bad as Breen's "Roman proof" garbage, or "wire edge" and other patently incorrect terms thrown at things out of ignorance or haste.

[Conder101]

No argument here, I prefer correct terms as well.

[messydesk]

I'm offering an explanation of a momentary explosion in the use of the word several years ago, not an excuse for it.

[RWB]

Understood.

 

I like that term: "momentary explosion" -- funny and appropriate, too. (I've had that happen after a generous meal of BBQ and beans.)

[19Lyds]

Sintering is a process of bonding metals together. Whether it is in parts fabrication where metal powder is compacted and then heated to produce a strong part or the simple act of a powder being bonded to a coins surface in much the same fashion as automobile wheels are "colorized" similar to simple xerography where powder is bonded to paper via heat transfer.

 

The term "sintered planchet" has been widely used amongst numismatists for many years and whether technically correct or not (think nu-cu-lar) it is accepted as meaning that, during the annealing process, something went wrong which discolored the planchets.

 

The US Mint has no definitive answer on how these anomalies occur and speculation has always been that left over copper dust in the annealing process, either from the tumbling of copper cents or the tumbling of 100% pure copper cored CnClad planchets was bonded to the surface of planchets possibly during a high heat event via the accidental introduction of oxygen to the annealing chamber.

 

True: "No U.S. coins were ever produced on purpose or by accident using sintering technology." when "sintering technology" is defined as the bonding of metal powder using compaction and heat to form a solid mass.

 

However, that is NOT to say that planchets have never received a sintered "coating" due to an error in the annealing process as we all know that this has in fact occurred.

 

 

NO, complete metal planchets have never been fabricated or produced using sintering technology BUT the basic sintering process, either accidental or deliberate, has produced planchets that are dark, and mottled in appearance with full mint luster due to high heat being introduced to the annealing process.

 

 

 

 

[WoodenJefferson]

I ran across "off colored' nickels in the 1950's. In a hand full of change you could spot them, along with discolored 'War" nickels...those 'off color' nickels became "Black Beauties"