While historical information about the Mint Of The United States At San Francisco ingots is generally nonexistent, I have had great success in acquiring a wide variety of examples and assembling my collection. Silver ingots produced by the U.S. Mint Philadelphia are much more scare as original production quantities were significantly smaller and distribution restricted.
Upon my initial introduction to U.S. Mint Philadelphia ingots a few years back, I was informed that the first hallmark was a Type II and the second a Type I. I have been so focused on Mint Of The United States At San Francisco ingot research that I have never really studied these until now. While recently working with Mark, researching a New York Assay Office ingot, it struck me that the above identification of these two hallmarks must be reversed.
Both examples above are dated 1946, in fact all but one U.S. Mint Philadelphia ingot that I have seen to date are dated 1946; I have seen one odd shaped example dated 1956. The 1956 hallmark matches the second hallmark pictured above and establishes one argument for identifying it as the last hallmark.
Throughout other government ingots, hallmarks standardized in later years of production and eventually all ended up similar to the U.S. Mint Philadelphia hallmark below establishing the second argument for identifying it as the last hallmark.
In my original post, working to establish the latest hallmark, I overlooked the fact that it is preceded by TWO rather than just one other hallmark. All U.S. Mint Philadelphia ingots are dated 1946, (one exception noted above), and I have found no numerical duplicates within the range of #3 to #308. In the next post regarding these ingots, I will show how the three hallmarks are randomly applied, to both obverse and reverse, throughout the entire series. For now, I present them in this order due to the first hallmark being applied to ingot #7 and the second hallmark not showing up until ingot #19. I should note that I have not seen photos of every ingot in perfect sequence so it is possible that a lower numbered ingot contains one or the other hallmark.
I now believe the U.S. Mint Philadelphia hallmarks should be identified as follows:
Type I or II applied to Obverse
Type I or II applied to Reverse
Type III applied to Obverse
Really looking for some help on this one, thanks.