After looking more, I found that it wont matter if I mix aluminum and zinc for my own use/castings.. It may actually end up resulting in better results. But if I want to sell ingots on eBay I should try and keep them separate, as I don't know what the end user has in mind. As long as I don't end up with magnesium in my furnace I'll be good as gold lol

I haven't tried the vinegar test yet, as I don't know if I have a piece of zinc (catch 22?), just found it interesting and hoping it works as a quick test. I'll keep a small squeeze bottle in the garage though. Magnesium on the other hand reacts vigorously with vinegar, for a much better confidence in result.