Definition Sought For 'Milk Spot.'

Milk spots are white patches sometimes seen on silver bullion coins, caused by residual planchet rinse solution. The spots are not usually visible on a freshly struck coin, they will form over time.

Is there any way to remove them?

To my knowledge, there is no way to remove milk spots. If there is a way, I'm sure it will do considerable damage to the coin.

As mentioned above, the planchets are not totally rinsed off before being stuck. Combined with the force of the strike the left-over residue is embedded into the coin.

Since this happens from the mint could these one day maybe be considered errors?

As I understand it, milk spots are formed when droplets of a salty solution - any salty solution - are splashed onto the coin and allowed to remain there. They are not formed purely or solely as a result of solutions sprayed onto the coin by the mint, so they cannot be considered mint errors.

In a sense they are similar to the "carbon spots" that form on copper coins, but the chemistry is different. For carbon spots, the causal agent is sulfur, typically derived from sulfur-containing enzymes in saliva and delivered to the coin surface when somebody carelessly sneezes, coughs or spits-while-talking over their coins. Milk spots are more likely to be caused by chloride, so things like sea-spray, brackish water, hydrochloric acid, sweat and tears can all cause them.

Chloride reacts with pure silver to form silver chloride, also known as "horn silver", a compound which is notorious for being difficult to remove from silver once it forms there. Anything aggressive enough to remove horn silver from a coin is going to damage the remainder of the coin surface too.