The claims I have heard about different mineral oils is that the difference is often in how consistent the particle sizes are. I have seen it claimed (probably by Norton and I am too lazy to look it up, which makes me think it might have been something from like $75 years ago) that mineral oils will have different size particles and that Norton's has very uniform sizes and, unlike some, will NOT dry out in the stone.

I have seen the claim that the oil can dry in the stone and gum it up, but I have never met anyone who has claimed that it has happened to them. One advantage to Norton is that it is food safe, but I would think that you could easily clean a knife that had something like Kerosene on it. It was mentioned that you can get food grade mineral oil by the gallon very cheap on amazon. I have a gallon of that that I use especially when I know I will be using lots of it like sharpening an axe. With my Norton sharpening station, I do use the Norton mineral oil.

I have always been concerned with using actual baby oil with other additives just because I am worried about them drying in the stone (again, not that I have ever heard anyone ever say that it happened to them, but I did see it written in some material). I expect that if you sharpen often enough it will no be a problem. I have let some stones sitting in a zip lock bag with lots of oil on them and did not have a problem and I could not begin to tell you what mineral oil I used on them. These were Norton India and Crysolone stones that still work fine even if I leave them sitting for some years before I get back to them.

What a great tip about checking the viscosity, especially if the bottle is clear; had not thought of that.

Has anyone even heard of somebody having mineral oil gum up (usually claimed due to evaporation of something or other) in a stone? I have heard of people cleaning stones that had things gummed up in them but the claim was generally not about mineral oil being left but more that the stone had not been kept suitably clean. If it was an India or Crystolone type stone they are cheap enough I would just replace it. An Arkansas stone I might worry about.