I've seen this a few times. I never knew exactly what it was but it usually comes off but there is staining left over. Here are a couple of explanations from Google.
*White rust* is a *white* powdery deposit formed from a natural *corrosion* process that can occur on any new zinc coated steel product. It is damaging to the appearance of the steel, not to mention to the anti-*corrosion* layer of zinc that protects the body of the steel. Galvanized *metals* also *rust*, but they do so at a slow rate unless the galvanized coating has been damaged. Brass, silver, and bronze tarnish as they interact with the atmosphere. Aluminum oxidizes into a *white powder*, although the *powder* binds chemically to the *metal* beneath, blocking further *corrosion*. On Fri, Dec 8, 2017 at 6:09 PM, Adrian Stoness via cctalk < cctalk@classiccmp.org> wrote: > water get sprayed on it? > > > On Fri, Dec 8, 2017 at 5:06 PM, dwight via cctalk <cctalk@classiccmp.org> > wrote: > > > Could be the zinc plating? > > > > Dwight > > > > > > ________________________________ > > From: cctalk <cctalk-boun...@classiccmp.org> on behalf of Sam O'nella > via > > cctalk <cctalk@classiccmp.org> > > Sent: Friday, December 8, 2017 2:46:40 PM > > To: General Discussion: On-Topic and Off-Topic Posts > > Subject: Types of corrosion on computers > > > > I've seen rust and dust, but there's an old vaxstation II at Goodwill > > Computers in Austin right now (very cheap, anyone welcome to buy it and > get > > it off my mind) but as most things, I checked out the back and see some > > circles of white corrosion on the back where the cards? are contacting > the > > case. > > > > I don't really have room or time but I don't own anything that uses QBUS > or > > is almost related to some of the neat iron some of you all collect (I've > > mostly collected way too many home computer history items). > > > > Anyway, what is that type of white corrosion on metal? Would one > probably > > assume this means any bus would be corroded and this wouldn't be a > computer > > for the faint of heart hobbyist? I've only seen that maybe from batteries > > but it's in an unusual place and pattern (I think). > > >