OT, sort of. What causes cast iron dust to bond to ceramic glaze?

[danlb]

I did not know that cast iron dust will bond to a ceramic glaze while it's busy rusting away. Any idea what's happening? Here's the back story:

I spent a while working on the lathe ate in the evening. Nothing big, I was just cleaning up some edges on a cast iron backplate for a 6 inch chuck. Like always, I ended up with black hands which I washed in the kitchen sink without clearing out the dishes first. Some time later I got around to doing the dishes. The dishes were previously rinsed so I dumped the water off the plates and put them along with the rest of the dishes into the dish washer. As usual, I got distracted and did not run the dishwasher till the next morning.

It ran. It dried. It did it's normal thing. But when I pulled out the plates several of them were covered with little orange dots. They were not just rust stains. I could feel the raised dots. Fortunately, I was able to get them off using "soft scrub" without removing the decorative pattern on the china. Good thing since the pattern is discontinued and replacements are $30 a plate.

What surprised me more was finding the large stainless serving spoon with similar problem and cured with the same solution.



I guess I need to replace the broken faucet in the garage utility sink. If the damage to the plate was permanent my wife would never let me forget it.

[754]

I noticed the toilet in my shop had rust specs. Then when I moved to a former tool and die shop, same thing..
It's metal dust on your clothes coming off , I suspect..

[danlb]

I guess I was not too clear. I fixed that in the first post. I washed the dust and chips off my hands and arms in the kitchen sink without removing the dishes first. They quickly filled with grayish water. I dumped the water out without being real vigorous about it, no doubt leaving some metal specs behind.

[old mart]

I remember glaze busting brake drums in the kitchen sink using 120 grit wet and dry paper and having a few tiny rust particles adhering to the stainless bowl.

[MattiJ]

Dunno what causes it but acidic wash gets rid of it. Phosphoric acid works well, citric should work too.

[Willy]

I have noticed an almost identical effect from cast iron brake rotor dust on not only the sides but on the backs of lightly colored cars. Like Dan said, not just stains but something that you could feel with your fingers and fingernails.
I've had luck removing them using Murphy's Oil Soap, I'll have to try a citrus based hand cleaner to see how that works.

[cameron]

Given the right conditions, those rust deposits on stainless steel can cause tiny pits in the stainless. The bottom of a pit tends to be starved of oxygen, and the metal in that region takes on a positive potential relative to the surrounding metal. With an electrolyte present, the pit area becomes a sacrificial anode to the greater area of surrounding metal, and the pit grows larger and deeper.

I have seen stainless steel pots of water kept on wood stoves for humidification develop leaks from pitting corrosion. The pits can occur on the side of the pot, and also on the bottom under a heavy calcium deposit.( Edit) Aside from a few pits, these pots were entirely free of corrosion.

Getting off topic here, but some time ago there was a thread about cupro-nickel and stainless steel brake lines. Because of SS's susceptibility to pitting corrosion, I suggested SS may not be the best choice of brake line for vehicles driven on salted roads.

[Joe Rogers]

New cars transported to a depot for later truck delivery suffer from “rail dust” contamination to the paint. Metallic debris airborn during the train ride and left on the upper surfaces will pit the paint clearcoat. The factories know about the issue and advise methods to mitigate it. So ferric debris and moisture is bad and should be preemptively treated before damage is present.
Joe

[J Tiers]

New cars transported to a depot for later truck delivery suffer from “rail dust” contamination to the paint. Metallic debris airborn during the train ride and left on the upper surfaces will pit the paint clearcoat. The factories know about the issue and advise methods to mitigate it. So ferric debris and moisture is bad and should be preemptively treated before damage is present.
Joe

I see a lot more new cars in transit with a protective film or paper on them. used to be just the snooty brands... Benz, BMW, and the like. Now I see many more doing that.