To avoid oxidization, I mix pure lead with wheel weight lead at a measure of 3 lbs of wheel weight lead to 15lbs of pure lead. The wheel weight lead will have other alloys in it that usually inhibit the oxidization process and allow for that nice shiny finish on the jig head. Running straight wheel weights will usually garner a harder head. The sprue doesn't bend and snap off as well and refining the head with a file or pocket knife takes more work than with a softer head.
When melting large amounts of lead down to ingot form, most guys "flux" their lead. This can be done a couple of ways. You can buy an over the counter flux to add to the pot or, like most guys, you can utilize parafin wax, bees wax, or a non sented, non colored candle. Most prefer the parafin wax added to the pot, skimming off the top, and then pouring the ingots.
As for priming: I would assume that means adding a top coat of paint or something else but I am not sure on that one. I have heard of guys pouring their jigs (in bulk) and then vacuum sealing them. Avoiding air will avoid oxidization. For me, I sell about 15k jigs during the months of January through April. Many of those jigs are poured at this time of year but not painted until winter. When using the above process I mentioned with mixing, I have zero issues with oxidization or heads that turn darker.
Interestingly, when utilizing powder paint, oxidation really doesn't matter UNLESS you are using candy colors. If using candy overtop of a lead jig, the shinny head will produce a different sheen than a tarnished or dull head. Coating candy over a different color than it doesn't matter. I'm not sure about Vinyl paint as I just don't use it.
Have fun and good luck