Dreaded Milk Spots

[Shamatti]

OK, time to have a chat about milk spots.

 

I just received a coin from a very trusted friend, and it arrived spotted.

 

 

 

Now, I have been told, and I believe without question, that when this coin was put in the post to me it was visibly in perfect condition. My supplier is not the sort of person who would send out a coin in this condition, especially not to a mate. So what happened? Spots like that don't appear overnight, do they? Or do they?

 

Here is my opinion: This coin was sent airmail. It would have been exposed to several dramatic temperature changes, not just during the flight, but also on arrival here in Portugal, where it is freezing overnight. Sorting offices, vans, post offices delivery van, bringing it into the warm house here etc etc. It is very possible that a very fine misting of condensation could have settled on the coin during transit. It is my opinion that these milkspots were already developing on the coin but that they were not yet visible. The slightest amount of condensation on the coin has made them visible.

 

This is the only theory I can come up with and I think it is interesting to the larger discussion on milkspotting.

 

Perth Mint are discussing milkspotting on an Australian forum, and the conversation is fascinating. Their materials scientists have tested milk spots and they are actually silver chloride crystals. They are always centred around an 'inclusion' - a foreign bit of material on the coins surface. Sometimes this inclusion stands on the surface of the coin, showing it got there after the coin was minted. Sometimes not, showing it was on the planchet before minting. So there is more than one cause of contamination of course. Perth Mint are making a very big deal of the work they are doing to prevent milkspotting in the future.

 

The discussion: http://forums.silverstackers.com/topic-59134-milkspotting-on-perth-mint-2015-kilo-kookaburra.html

The photographs: http://forums.silverstackers.com/topic-59730-exclusive-to-silverstackers-electron-microscope-images-of-white-spot.html

 

It seems that there is still a lot of work needed by various mints regarding this issue. However, two things become apparent: It is more likely humidity than oxygen which is causing milkspots to appear. You can't tell by looking at a coin if it has milkspots already which will appear in the future.

 

My friend expect me to be angry about this. I'n not really. Perhaps a little disappointed, but like I said - this coin would have spotted at some point in the next few years any way, so nothing has changed. The spots were growing there, albeit not yet visible. And who knows - by the time my stack arrived here from storage in a few months time, my other RM products - my other mule even, might also have developed spots! You pay your money you take your chances with silver. Hey Ho!

 

PS - I'll not be trying to clean them. As the man from Perth Mint said "...our Chemist does not recommend this as the formation of the white spot causes the silver in the coin to become consumed resulting in a recessed area..." cleaning the coin could leave a worse finish than you started with.

 

 

[Pete]

As some coins develop milk spots but others don't, even from the same Mint, this would eliminate environmental conditions.
Need to focus on the press and any cleaning / cooling liquids.
If there is a solvent or cleanser that is recycled, perhaps after a time it needs replenished but one press has more use out of the same solution ?
I have hundreds of Maples with no milk spots but I have a few with spots.
That would also eliminate also, I think, the blanks.

Once upon a time an employee in a factory was wearing a special ring and minute quantities of one of its rare metals contaminated an ultra pure alloy. This resulted in a new type of photon detector and it was a long time before this invention was discovered. Maybe there is something like this happening in the Mints ? Lunch box, overalls, hair gel ? Who knows ?

[Shamatti]

As some coins develop milk spots but others don't, even from the same Mint, this would eliminate environmental conditions.

Need to focus on the press and any cleaning / cooling liquids.

If there is a solvent or cleanser that is recycled, perhaps after a time it needs replenished but one press has more use out of the same solution ?

I have thousands of Maples with no milk spots but I have a few with spots.

That would also eliminate also, I think, the blanks.

Once upon a time an employee in a factory was wearing a special ring and minute quantities of one of its rare metals contaminated an ultra pure alloy. This resulted in a new type of photon detector and it was a long time before this invention was discovered. Maybe there is something like this happening in the Mints ? Lunch box, overalls, hair gel ? Who knows ?

 

 

I think you should read what the metallurgists at Perth Mint have to say on the subject.

 

If the contamination causing the spot is pressed into the coin then it is a sure sign that it was on the planchet or the die, as it must have been present at time of minting. If it was not it would stand proud of the coins surface. (As some do)

 

In the case of Perth Mint coins which are capsuled at the mint, there is only 1 possible place where that contamination could have been introduced, and that is at the mint. This is why they are spending millions on maintaining/improving those environmental conditions at the mint.

 

In fact both cases are true. They have found spotted coins which have been contaminated before/during minting, and those which have been contaminated after minting. This shows that there is obviously more than 1 source of contamination. This is true for Perth Mint, I would guess it is also true for other mints, but they are not all talking about it like PM. Kudos to them for being so open about it I say.

[HighlandTiger]

Just one thought here. We don't see these milk spots on older coins, such as the Sterling silver crowns etc. So there must be something in the process today that is different to the minting processes of years gone by.

 

I think that is as good a place to start looking as any other. 

[Shamatti]

Just one thought here. We don't see these milk spots on older coins, such as the Sterling silver crowns etc. So there must be something in the process today that is different to the minting processes of years gone by.

 

I think that is as good a place to start looking as any other. 

 

Agreed. Someone on the other forum said that in the case of Perth Mint he had never heard of a coin spotting if it was made before..... 2009? TBH I can't remember exactly but it was something like that.

 

I would like to see RCM pay as much attention to their customers concerns. But as far as I can tell, all they have managed to say on the subject so far is 'So what. it bullion, who cares?' or at least to that effect.

[Danny-boy]

I'm still gobsmacked that it happened in transit!!!

[JayB]

Comment from a newbie: When you say milk spot, do you mean that horrible blob on the 'II'?

 

Tbh, I first thought it was condensation inside the capsule!!!

 

I'd heard of this but had never seen it before. A dreadful blemish on a beautiful coin.

[Pete]

I have never seen a milk spot on a sterling silver coin and I assume the minting process is the same so that does point to a chemical reaction with the metal. Fine silver appears more susceptible than 92.5% silver so can this be extrapolated to the criticism of the RCM who use 9999 silver rather than 999 silver ?

In the same way a pure breed pedigree dog is likely to suffer more skin and other disorders than a mixed breed mongrel - is a super pure coin more prone to chemical / agent attack than a coin containing some other 'stabilising' ingredients ?

 

Fluttershy - where are you on this topic ?

What does a chemist working with silver reckon ??

[HighlandTiger]

I have never seen a milk spot on a sterling silver coin and I assume the minting process is the same so that does point to a chemical reaction with the metal. Fine silver appears more susceptible than 92.5% silver so can this be extrapolated to the criticism of the RCM who use 9999 silver rather than 999 silver ?

I

 

I had forgotten that the RCM uses .9999 silver, with sterling silver coins not spotting at one end of the spectrum through to the RCM who uses the purest form of silver for its coins at the other end of the spectrum, you may be on to something.

[Shamatti]

The Britannia is 999 pure silver. I expect the reason sterling doesn't spot is being an alloy the AgCl crystals are unable to form do to a lack of pure Ag to bond with. Don't know, I'm guessing to be honest. But it seems logical to me.

[morezone]

Milk spots strike again.

Just took delivery of a tube of 2015 Britannias and already some are beginning to spot.