Following on from this topic http://forums.silverstackers.com/topic-59134-milkspotting-on-perth-mint-2015-kilo-kookaburra.html I've been having a chat with our Chemist/Metallurgist about white spot and he kindly provided the scanning electron microscopy (SEM) images of white spot below (with my non-techy description). Brainy white spot Blob white spot Moon crater white spot These images show a small selection of white spots we have seen over the years. Note that these are images of the "inclusions" at the centre of the spots, not the actual spot themselves (which is just AgCl crystals as seen surrounding the defect in image 2). We know the white spot/milky blotch stuff is AgCl, but what makes elimination of them from our process difficult is that there can be multiple causes of the spots as you can see from the images, they are not all the same (although visually they all look like a white spot to the human eye). Note that it is a piece of debris/inclusion that causes the formation of AgCl, which results in white spot. In some cases the debris/inclusion is in the metal of the coin, in others the debris is raised above the coin surface, indicating that it had settled after striking. Debris can come from such things as poor water quality, cast in crucible material or struck in debris and you get different types of white spot depending on the source of the problem. It is highly likely the recent "outbreak" isn't the same as the defects appearing on older coins. We are certainly ensuring our air and water filtration is up to standard and running as clean a factory as possible. Regarding suggestions on how to remove the white spot from coins, 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, which is apparently obvious in the first image (although I just looks like some brainy looking virus on the coin to me). As a result attempting to remove the white spot could result in making the finish of the coin worse. Of course I don't expect this will dissuade cleaning experiments and I'm sure all silverstackers look forward to the results of the proposed cleaning methods. You might just want to run them on coins of varying age to ensure your method work on all different types of white spot.