Is this Tanin staining?

[Andy's Shed]

Yesterday I turned a bowl from an Oak crotch that I'd been given and as it still had a high moisture content, I'm expecting some wood movement, cracks, etc.
I brought it indoors and I'm just going to leave it to thoroughly dry out, but this morning I noticed some grey coloured blotches and patches in places.

Is this the Tanin in the wood rising to the Surface and is it likely to remain once the bowl has dried? If so, what would be my best bet to try and remove or reduce it?

Here's a photo of one of the offcuts. Thanks

 

[Richard_C]

You get that if there is a reaction between the tannins, particularly but not exclusively in green oak, and ferrous metals. Has it been in contact with steel? A few weeks back I sanded a small piece of well seasoned oak on a belt thal had also been used to sharpen a chisel, my mistake. Glued it up, a day later there were black lines ion the joint. You can get staining where the chuck contacts the bowl tenon or recess as well.

 

[Phil Pascoe]

The staining might be shallow as it might have been just brief contact with the saw chain that caused it. You'll not know til it dries. You might have some luck removing the stain with oxalic acid.

 

[Andy's Shed]

Thanks Richard and Phil, yes it's likely from metal tool contact.

I have since done some searching online and Oxalic acid was mentioned in several videos, we have some Barkeepers Friend cleaning powder and it contains Oxalic acid.

I did a test spot in the centre of the oak cutoff and it did a good job of removing the stain. After seeing the test result, I've just gone over the bowl and it's looking much better now. Many thanks again.

 

[Richard_C]

Oxalic acid, hmmm. Maybe we should wrap our oak bowls in rhubarb leaves for a few days.

 

[Phil Pascoe]

Worth a try on some scrap. Macerate a few, who knows?

 

[the great waldo]

You get that if there is a reaction between the tannins, particularly but not exclusively in green oak, and ferrous metals. Has it been in contact with steel? A few weeks back I sanded a small piece of well seasoned oak on a belt thal had also been used to sharpen a chisel, my mistake. Glued it up, a day later there were black lines ion the joint. You can get staining where the chuck contacts the bowl tenon or recess as well.

If you use titebond it reacts with iron leaving black marks. Steel sash clamps without masking tape over them are a no no for panel glue ups.
Cheers
Andrew