Opinions on Silver Krugerrand coins?

There was a good article on milk spots here ages ago - might have been by Bron. Well worth a read. Electron microscopy revealed that the spots may be reactions to tiny inclusion bodies such as airborne particulates settling on the surface of the coins in the manufacturing process.

If spots are surface only and this is the reason (you’d have to do a more detailed study to see if the spotting process occurred subsurface) then no capsule can fix. Given that the process happens more with some mints rather than others, you’d have to wonder if other issues are relevant, such as ambient temperature, rate of cooling, humidity etc.

It has happened with Perth Mint items but almost everything I have is clean. The main example of milk spot I have of that is a kilo PM dragon with diamond eyes, on the obverse. Needless to say this is well known in maples (including mine).

Best way is to buy things which don’t spot. You’ll only know well after they are minted, so maybe best to avoid new items.

Agree about the price issue (supply and demand). Some of my oldest purchases were Libertads as they were close to spot from a dealer a decade ago. Nobody wanted them, no demand.
 
minimilled said:
There was a good article on milk spots here ages ago - might have been by Bron. Well worth a read. Electron microscopy revealed that the spots may be reactions to tiny inclusion bodies such as airborne particulates settling on the surface of the coins in the manufacturing process.

If spots are surface only and this is the reason (you’d have to do a more detailed study to see if the spotting process occurred subsurface) then no capsule can fix. Given that the process happens more with some mints rather than others, you’d have to wonder if other issues are relevant, such as ambient temperature, rate of cooling, humidity etc.

It has happened with Perth Mint items but almost everything I have is clean. The main example of milk spot I have of that is a kilo PM dragon with diamond eyes, on the obverse. Needless to say this is well known in maples (including mine).

Best way is to buy things which don’t spot. You’ll only know well after they are minted, so maybe best to avoid new items.
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That's sad, I was hoping they formed as a reaction to oxygen or something. I have watched a video where the guy removed them easily with an eraser (rubber). I doubt that would damage the coin so it might be a good solution for stackers... probably not a great idea for collectors just in case it creates micro scratches.
 
Calendyr said:
That's sad, I was hoping they formed as a reaction to oxygen or something. I have watched a video where the guy removed them easily with an eraser (rubber). I doubt that would damage the coin so it might be a good solution for stackers... probably not a great idea for collectors just in case it creates micro scratches.
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The milk spots are Silver Chloride and appear to be caused when the planchet is cleaned with Hydrochloric Acid and not washed properly. Some of the HCl stays on the silver and slowly reacts to form the milky white AgCl. It is a very slow process and, as you said, only takes place on the surface of the metal.
 
I wonder if you could soak the coins in a solution that would neutralize the acid before it creates the spots... something like baking soda in hot water maybe. What do you guys think?
 
Be careful adding other chemicals, you may end up with Silver compounds of all different types. Your best bet is to use distilled water (no other contaminants in it) and just wash it over the coin. You have to do this before the milk spot has formed as Silver Chloride is insoluble in water. The chloride ion from the acid will dissolve in the water and be washed away.
 
Ian Gillman said:
The milk spots are Silver Chloride and appear to be caused when the planchet is cleaned with Hydrochloric Acid and not washed properly. Some of the HCl stays on the silver and slowly reacts to form the milky white AgCl. It is a very slow process and, as you said, only takes place on the surface of the metal.
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Sometimes/very rare/it can do deeper-all depends on the water contamination and how good the planchet has been cleaned.
 
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