Est. 1998 — 27 years of woodworking knowledge
What is this discoloration?
David Weaver
Fresh green blank of one of the granadillos. Turned yesterday and was clear.
This morning, the wood has this discoloration forming. Is it a reaction with oxygen? Could hardly be mold as the bench is 38 degrees F, and that is where it has been the whole time. 
To be clear, these were from a blank that was waxed and I cut them and turned them so that they can be used later for handles.
Re: What is this discoloration?
Oskar
is the wood tannin rich? Could it be iron dust/steel filings (perhaps from hands that have been sharpening) getting stuck in the pores and then turning black/dark ?
My thoughts as well.
Re: What is this discoloration?
David Weaver
Not sure. When it's labeled granadillo , it could be a half dozen things, and this wood is much different than the other granadillo I've gotten.
Its It's possible that it contacted metal dust.
Re: What is this discoloration?
Warren in Lancaster, PA
This stain forms when green wood with tannin is worked with iron planes. The stain is iron tannate. It is just the right color. We see it a lot with green white oak.
What we usually do is wait a day or so for the surface to dry and then take a light shaving off the surface.
You can dissolve it with oxalic acid (it forms complex ions), but usually the planing method is easier.
Re: What is this discoloration?
William Duffield
I agree with Oskar and Derek. I've had it happen with oak and mahogany that got too close to steel filings/grindings, and even with our local tap water that is high in iron used for raising grain.
Re: What is this discoloration?
Don Stephan
If black iron stain like what happens turning green red and white oak, lemon juice has been suggested on another turning forum. The suggestion went on to advise brushing lemon juice on the entire surface while the wood is wet, to minimize chance of uneven wood color after drying.
After noticing black smears on green red oak bowls being turned, I started using an inexpensive acid or glue brush to wipe away collected wet shavings/dust that collects in the gouge flute, rather than wiping away with my fingers. My reasoning was that as the wood is cut, the gouge cutting edge is being worn away (iron dust) and collecting with the wet wood in the flute. Using the brush has eliminated the black smears, presumably from my hands, but not the occasional black flecks like those in your photo.
Re: What is this discoloration?
David Weaver
Before reading through these posts this morning, I card scraped some of it off (similar to your suggestion of planing). The top surface is no longer wet and it doesn't go very deep, and these will be turned down later when they're dry to make handles.
I've seen green stains on oak before, but hadn't considered it on tropicals. This wood reminds me of oak but more dense with a little bit of a peppery oak smell (it's sold as granadillo, but it's not as nice as the others that I've gotten - this is coarse, wet and stringy whereas the other was finer and darker).
There's plenty of metal dust around my shop right now - if a plane sole can stain it, then even though I don't see standing dust on my bench top, there's plenty there for this.
Re: What is this discoloration?
Jerome
Weird, i have been using acid (vinegar) to dissolve iron wool into an iron acetate solution to ... blacken wood. I would have gone with baking soda as a base to prevent the reaction with the iron particles.
Lemon juice or vinegar can help dissolving the stain later however.
why lemon juice was suggested
Bill Tindall, E.Tn.
Not because of acidity but because citric acid makes a colorless compound with iron, just like oxalic acid. Most other iron compounds are highly colored.