Here is probably the best paper description, written by Russell Wanhill in 2005. So keep in mind, the New Jersey Zinc company created the early Zinc 3 alloys etc as a result of the earlier problems and this is where early limitations on impurities were defined. One thing I have noticed is that it is repeatedly stated in publications that high quality zinc is difficult to make and you can't do that by starting with lesser grades, or re melts etc. It is very easy for off shore production to be susceptible to this problem if they are not using high quality zinc to start with. Low dollar wins the bid, and there is a big relative price difference to get the good stuff. Also, for the most part Lionel/MTH/etc, will not "see" a defect since the failure will not occur until later.
