Posted By Ron Currie

BULLION BARS AND COINS

Milk spot (or white spot) is a topic that other mints rarely like to discuss. In view of recent concerns expressed about this general lack of transparency, I’d like to get on the front foot and tell you what The Perth Mint is doing to minimize the problem.

Milk spots are opaque, cloudy blemishes that can appear on silver coins after they have left the mint. The vast majority of Perth Mint silver coins are unaffected by this issue. However, when they do appear, it’s understandable that investors and collectors are concerned.

Milk spots have been attributed to a range of potential causes. In our experience the exact reason is difficult to pinpoint, with recent analysis effectively ruling out crucible contamination and water quality issues.

Now, Perth Mint metallurgists are working on the theory that microscopic airborne particles are largely to blame.

Although not conclusive, investigations have found a minute piece of debris at the centre of milk spots on a couple of affected coins. Surrounding each ‘inclusion’ were silver chloride (AgCI) crystals which created the milky blotch. In a further discovery, each piece of debris was raised above the coin surface, indicating that it had settled after striking.

More work is being carried out to confirm the composition of the debris but our immediate response has been a comprehensive cleaning program for the removal of dust and microscopic debris from all production areas, including the trolleys used to transport coins around the factory.

All compressed air line filters have been cleaned to eliminate oil and water build-up, while our air conditioning filters have also been replaced to prevent airborne particles from entering the production areas.

Each of these actions is scheduled to be repeated regularly.

Finally, we’ve started quarantining some product before shipment to monitor whether this approach is working.

Fortunately, it seems that The Perth Mint is not as badly affected by this perplexing problem as some other mints and I’m pleased to report that we’ve already seen some further reduction. While it remains exceptionally difficult to eliminate completely, I am happy to reassure customers that we will never duck this critical issue as we seek all possible means to minimise its occurrence.