If Milk Doesn't Cause Milk Spots, What Does?

Coinosaurus

I've heard tales of cyanide and coins, but never milk and coins. What REALLY causes milk spots?

JL3Eleven

Answer that and your a made man.

sinin1

silver chloride

BAJJERFAN

Yes, the principal culprit seems to be chlorine, possibly from some sort of bleaching step.

7Jaguars

Ditto that, BF and all beat me to the punch...

BillJones

Unfortunately the cleaning agents that the mints use for cleaning planchets seem to be the root of problem. It’s a shame that the mint can’t get this right on a consistent basis. The problem has been around for many years. Those who collect Liberty nickels know that the 1912 –S and D coins in uncleaned, Mint State condition are virtually always toned to an unappealing brown color.

keets

JMHO, but the term "Milkspot" as i understand it was originally used to denote spots on Proof coins which were the result of incomplete removal of the the rinsing agent used on planchets prior to striking. from that perspective, Milkspots are really a strike-through and have become a part of the coin's surface, rendering them unable to be fully removed. sometimes the appearance can be helped so they don't look as bad, but Milkspots can never be fully removed. also, they may not be visible at the time the coin is struck and tend to develop visually over time since that area of the coin's surface is chemically different. i'm not certain what BillJones is referring to or what sinin1 is referring to, those things seem like they are more of a toning phenomenon.

i have always understood Milkspots as a pre-strike issue, not post-strike.

ricko

Although the substance is known, the real reward would lie in finding a method to remove the spots. Unfortunately, by the time they develop, the surface below is marred. A key step is dipping the coin in reagent grade acetone upon receipt and proper rinse and dry steps. This seems to prevent the development of the milk spots. Cheers, RickO

RWB

The processes and materials used to "whiten" planchets before use has changed many times over the last century. Planchets for nickels have been purchased ready-to-use, from contractors since the 1880s, so blaming the mint for the color of 1912 coins is meaningless.

notwilight

<< <i>JMHO, but the term "Milkspot" as i understand it was originally used to denote spots on Proof coins which were the result of incomplete removal of the the rinsing agent used on planchets prior to striking. from that perspective, Milkspots are really a strike-through and have become a part of the coin's surface, rendering them unable to be fully removed. sometimes the appearance can be helped so they don't look as bad, but Milkspots can never be fully removed. also, they may not be visible at the time the coin is struck and tend to develop visually over time since that area of the coin's surface is chemically different. i'm not certain what BillJones is referring to or what sinin1 is referring to, those things seem like they are more of a toning phenomenon.

i have always understood Milkspots as a pre-strike issue, not post-strike. >>



The mint rinse, and chlorine are the internet lore but I've never seen any hard evidence.

On the other hand, I sent a milkspotted ASE in a PCGS holder to a top engineering lab that I use for engineering failure analysis (my other job) and found no chlorine at all in very sensitive trace elemental analysis. --Jerry

swhuck

Cows.