Milk spotting/hazing/clouding has gone through lots of theories and speculations over the years. Hard to pinpoint the true causes 100% because the mints themselves aren't giving much away when it comes to their processes. But there are plenty of snippets which can be put together.
Some mints are doing things which end up with milked coins. And some mints are doing those same things, but they introduce extra measures to reduce or even eliminate spotting/hazing. These extra measures can have haphazard results or completely successful results depending, i reckon, on how fastidiously they do it at any given time. So what is it they might be doing or not doing - i'll come back to that.
There are small independent mints which do not produce milk stained coins at all. It seems to be an issue with the big volume guys. Which could point to the endless cost saving techniques the paper shufflers in every large company come up with to justify their positions to the CEO. Where the margins become more important than the quality of the product. Whereas the smaller outfit needs the quality to speak volumes.
So what sort of thing are the mints doing and not doing. Mints have always been using washes and detergents during the processes, most likely taking the correct steps and time needed to remove all residues. Sure, sometimes coins would get through and go on to develop some spots but for the large part, not on epidemic levels. Along come ever improved machines which can mint coins faster. Has some of the time and attention given to cleaning the coins been sacrificed to keep up with output? Also, along has come special chemical lubricants which, when the planchet is pre-washed in it just before the strike, results in a crisper finish and zero chance of particles sticking to the surface.
Dies are expensive, too. These new lubricants also serve to extend the life of the dies. At least doubling (tripling if really pushing it to the limit) the number of coins a single die used to be capable of producing.
So these advances have been great for mints in increasing output and producing great crisp looking coins to begin with, anyway. Saving costs of materials and man hours. But they have not kept up the quality of the complete removal of these chemicals from the surfaces of the coins. They know how to solve it. Correct washing and rinsing. The thing is, that costs time and money too. Somewhere along the line it got reduced and reduced, depending on the final product. So basic bullion – basic wash. Proofs – a much higher degree of attention to cleaning. Yet, a laziness has crept into the proof process as well, with more and more instances of spotted proofs.
In answer to the milking problem, rather than have it known they prefer cost saving over quality, some of the mints have had contempt when the issue became a concern with buyers. Saying it is a mysterious development, they will look into it, but in the meantime it’s just bullion folks so what do you expect. Perfection? Pah.
And this is where you get the divergence between mints. Some address it and put in the correct steps to prevent, even if it is just bullion. Because some mints just do care more than others. I suspect that the RCM (still perpetuating the mythical unknowns of milking) have only come up with this new coating because of the slump in the bullion coin numbers. They would have us believe their “scientists” have developed this wondrous solution after years of toil. Oh really RCM? After years of telling buyers to like it or lump it when it came to milking? Also, it points to this coating being actually a cheaper method in the long run than actually cleaning the coins correctly. You’ll find they crunched the numbers on that one. Just to be clear too, this coating will substantially reduce milking, not eliminate it (from their own press release). So not a real attempt, just a PR stunt.
Other mints like Perth are doing the necessary needed to largely eliminate milking on their premium bullion ranges. They at least are taking pride in those ranges. But less so on the low premium stuff (anyone remember the milk state of the Funnel Web Spider bullion?). There is also a pattern in that the low premium stuff now gets a all-over frosted finish. Milk hazing will happen but it’ll be less obvious. Like the latest rectangular dragon.
So yeah, they all know the cause. And some deal with it better than others. All of this is just my own belief based on reading many obscure articles and talking with others over the years.
As to why all the mints seem to prefer to shroud the whole milking issue in mystery? Well, think about it. Who wants to be the first to say publicly ….. um yep, I guess we could wash/rinse/repeat everything a good while longer.