The black color is from the interaction of iron with tannin's in the oak. Although it looks bad, the amount of iron lost to it is infinitesimal. Some people actually use this reaction to "weather" (think barnwood) oak and some other woods by dissolving some steel wool in vinegar then painting the solution onto the wood. The acidity is probably important to dissolving and keeping the iron in solution, as iron (Fe^3+) is not very soluble at higher pH.
I spent a period making green-bent chairs out of oak, and the thin back splats were bent into the chairs green. I'd rive the back splats out of green quartersawn (er. . .quarter split) oak then hand plane them to final thickness. I had to use a wood bodied jack plane for this, because iron-bodied planes would turn the whole thing grey (wet wood). Oxalic acid can be used to bleach the grey out if need be.
As far is actual pitting tools/lathe beds, I don't think (from my own observations, not science) oak is substantially worse than other woods with high moisture content -- any of those will get rust going if you leave them on unprotected surfaces. Oak just looks worse because of the grey/black color.
Beyond wiping down the ways of the lathe, one place it's easy to forget is the shaft of the tool rest and the hole in the banjo. Learned the hard way that when turning wood that is actively throwing water, it can seep down in there and cause a mess. Now after turning green wood I always remove the tool rest and wipe it down, then spray compressed air down the hole in the banjo.
Best,
Dave
I am wondering about the lathe tools getting pitted. Never happened to me. I do get some coloration on the sludge that builds up on the tools, but nothing that actually discolors the metals. I turn pretty much only with Thompson and D Way tools.
robo hippy
This is exactly why I don't turn green Oak. Was a bad experience for me and not worth the effort!
Pete
* It's better to be a lion for a day than a sheep for life - Sister Elizabeth Kenny *
I think this equates nicely to wood turning as well . . . . .
If I'm turning wet oak, I put a sheet of plastic over the ways and then dump it and air-spray the bed when finished turning. Pre-applying WD40 or Boshield, etc. to the ways before covering them also is a good idea.
Also, I will sometimes put some stretch wrap or saran wrap over the chuck jaws, especially if I'm going to leave the piece chucked up for a few days. The reason for that is that it keeps the chuck jaws from leaving a black stain on the tenon or mortise - - plus also keeps the jaws from turning black.
Those are some good tips. I did apply some CRC 3-36 before turning, but I still had staining issues. The saran wrap would have definitely helped the jaws though, there is some pitting, and it left the black stain on the tenon as well.