"The Perth Mint has also taken steps to both identify and try to tackle the problem. Two years ago officials at Perth said that, after ruling out suspicions of "poor water quality and crucible contamination," that "an accumulation of microscopic silver chloride debris are responsible for leaving the blotches." As a result of these findings, the mint implemented some measures to reduce the frequency of the spots, including "routine cleanings of its airline filters so as to remove any oil and water build-up" and "replacement of its air conditioning filters" to eliminate the chances of "airborne microscopics" appearing in any of the areas where coins are made.
Those efforts appear to have been successful in reducing the number and frequency of milk spots on coins from Perth, but according to many posters at the SilverStackers forum, the issue continues to plague coins from this mint. I found their comments surprising, since I have not seen a lot of spots on Perth coins I have purchased.
LOL, I'd say this is a direct reference to the recent Perth Mint Milk Spot discussion thread
I agree with this author, I too have not seen a lot of spot on Perth Mint Coins, but obviously a lot of members here have