Flash rust

I was honing a razor just a little while ago that I had hand-sanded to a decent shine. My son stopped by to borrow a book so I was interrupted for maybe 5 minutes--- yeah I forgot to wipe the blade off before I set it down ---- the razor rusted in that 5 minutes! It cleaned up (for the most part) very easily, but I was a little shocked. Does the sanding make the blade more prone to this?

the only explanation for this i can think of is it was the very fine metal particles sitting on the surface of the blade from honing that actual rusted having a very large surface area the should oxidize very very quickly. thats my thoughts as a scientist anyways maybe someone who knows more about honing than me will have another reason for this

Yes, once all the oils and waxs are removed from carbon steel you can almost watch it rust before your eyes if left wet.

Silver2

I think our water quality fluctuates and could be more acidic at times. Because every time it has happened some baking soda stopped it. It being water stone polishing steel that oxidizes as you watch. And the same piece might not rust next time without using soda.

with a higher polish say 4kjpn I cant recall it happening, but if it is in O and water it is oxidizing

When I was polishing swords, I would use a little baking soda (a big pinch) in my water bowl that I used to sprinkle my stones. I have continued to use this method and have not ever had a razor to "flash rust". It will happen quickly with some water, steel, or a combination of both.

If I need to walk away even for 30 seconds I dry the blade. Just a quick wipe.

This actually just happened to me. It was only my second razor that i have tried honing. This post makes me feel a little better knowing that it is possible, coz i thought i was going crazy.

the more ridges in the steel the more places that rust can start
the finer the finish the less problem
its all about how the water interacts with the steel (surface tension of the water ) thats why mirror finished blades tarnish slower and rust less

bead blasted SS blades in the knife world are more prone to rust then mirror finished carbon
other thing is if a SS blade is ground on a belt that been used to grind a carbon blade micro bits of carbon steel can get stuck to the SS blade and make for a starting point to rust (random pitting )

depending on HT that too can cause more or less possible rust points