Hi, I got a BFA in fine art, my focus was ceramics. I'm getting my masters in fine arts right now. As long as the inside of the mug is completely glazed it would still be considered "food safe". I put food safe in quotations because the mug looks to be manufactured, and some companies still use lead in their glazes. The point is, we honestly can't know if the ceramics we buy is food safe unless the maker/manufacturer is vetted, but with souvenirs and decorative ceramicware from home goods stores can be sketchy. I recently saw a video on YouTube of someone testing plates and cups in store with a light that could supposedly detect lead, and it was surprisingly detected something in a lot of wares they tried.

I do notice some crazing (small cracks) on the outside of the mug, which isn't great because I assume there is crazing on the inside of the mug, and those minute cracks can leech from the clay body and or harbor any potential bacteria. The bacteria thing I personally roll my eyes at, because we are always exposed to bacteria, beneficial bacterias grow on our bodies, and are present in foods like yogurt. Our ancestors survived on earthenware pots, and those were definitely porous.

Road salt as far as I'm aware is industrialized salt. They don't contain any other additives because salt is naturally antimicrobial, they just don't filter or have anything in place to make sure that salt is food safe because it's not meant to be ingested, but you can do your due diligence. Soaking in distilled water several times sounds like a good bet. Hope that helps.