Sintering, How Can You Tell? And What Exactly Is It?

It is a little tricky to explain so bear with me. Also, If anyone wants to ad, or clarify this, please be my guest.

During the process of minting a coin, there is an annealing process that takes place. Annealing is the heating of a blank, or a planchet to soften the metal in preparation for subsequent striking of the planchet. (Dies are also annealed during their manufacture but that has nothing to do with this) We are talking about planchets right now.

Annealing takes place in large drums.

Now for how a sintered planchet happens. With circulation coinage, If the annealing drum is not cleaned properly between applications and different blanks are annealed one after another, metal from the previous batch of blanks can be deposited on the current batch of blanks.

So, if cents were annealed and the annealing drum was not properly cleaned, some minute amounts of copper would likely be left behind in the annealing drum. If, as in my example, quarter dollar blanks were annealed after cent blanks, some copper would adhere to some of the blanks. Some could become completely copper colored, while some may just have streaks of copper that adhered to the surface of the blank.

According to the US Mint, Blanks are annealed then sent to have their edges upset thus creating planchets. Any of the effected blanks would therefore become sintered planchets at this point.

In the picture, The quarter on the right has was struck on a sintered planchet. The picture was done quickly so it's not the best, but you get the idea.

The dimes shown above are damaged and not struck on sintered planchets.

Thanks,
Bill

Looks like the first one was colored with a magic marker?