Both Viginia and Smithfiled hams are salted and cured in the Sodium Nitrate/Nitrite solutions. They may or may not be dried, I don't remember which is and which is not. Prosciutto hams are made much the same way by salt curing and air drying with no other treatment.
One type is soaked in water before cooking or is cooked in water that is discarded. The other can be eaten directly if properly cured and or smoked during the curing process. They may be 'cold' smoked or 'hot' smoked just as fish is often smoked both ways.
As for your procedure with Borax, yes, it requires repeated recrystallizaations to work properly and does depend heavily on the types of impurities present, but I stress REPEATED recrystallizations as you stressed. One sequence will often not work and this is what you have to understand. This involves so much extra labor and uses so much water (as I said in previous posts) that the user is well advised to buy pure product to start with or the cost will soar.
I think that this is going quite astray by trying to prove that lower quality materials can be used. They can work, but you can also pay a price in terms of quality that can bite you in many different ways as I have pointed out before.
I should add that not knowing the starting purity of an impure substance often leads one to using an incorrect number of recrystallizations. I had to run purity tests after each recrystallization that I ran in graduate school to prove the purity before I sent it out for analysis to get the 'final' purity verified. We did much the same at Kodak.
I remember one chemical that was so difficult to make and purify that they used the largest reactors to run it and ended up with a tiny bottle of photograde material at the end which was worth thousands of dollars, just to get the purity level needed. It was an ingredient that went into an emulsion.