Oak turning black wherever bare metal touched it

[Joe Hillmann]

I was working on making some toboggans today out of freshly cut, still wet oak (It was cut from the log this afternoon). Anywhere that cast iron touched it it is turning black/blue. How can I prevent the wood from changing color and how can I get rid of the discoloration that has already happened?

[Dave Cav]

The tannins in the oak are reacting with the iron or iron oxide and making the black stain. Oak is notorious for this and with wet, unseasoned oak and cast iron you have a worst case scenario. You would need to separate the materials, dry and finish the oak to prevent this from happening. In my experience the black stain penetrates a ways into the oak but if you catch it soon enough you may be able to sand it out, or you could possibly bleach it out. Oak will also corrode ferrous metals. If you ever make a jig out of oak and then take it apart years later you will find quite a bit of corrosion on the fasteners.

[Jim Riseborough]

I had this too, I used some steel blocks to flatten a joint during a glue up. It left a black mark. sanded right out tho.

[Brian Tymchak]

Try oxalic acid to bleach the stains. Here's a thread from the past on that topic: http://www.sawmillcreek.org/showthread.php?136984-How-do-I-remove-black-stains-from-oak

[george wilson]

We made an excellent black dye with oak sawdust,vinegar and iron filings. 200 year(or more) way to do it. Not sure if bleach will work. You used to could get 2 part bleach for removing stains in wood. It may still be available. The oak will do this staining till it is bone dry. Even then,you'll have to varnish it well with spar varnish before adding iron parts.

[Mark Wooden]

Oak tannins and iron don't mix- but you know that now. Since the wood is screaming wet, you should be able to take a sharp chisel and pare the stained area off, you could try a sharp shavehook also; sanding would just load the paper in an instant unless you're using 36 grit and coarser.
To prevent it from happening, get some canning wax at the grocery store and rub it on the tool surfaces that will come in contact with the wood. Refresh it while working as it will rub off. I always hit my bar clamps with wax before I do a glue up with any wood, it stops the marks and the glue squeeze out doesn't stick to the clamps

[Jim Andrew]

There is a company called "Soap Goods.com" that sells oxalic acid reasonably priced. Too bad the postage isn't. I ordered some, they have a package of 1 1/2 pounds for 4.00 plus change. The postage was 9.00something. I have a motorcycle tank that is rusty, it is supposed to clean out the rust, not hurt the metal, and remove the black stains from your wood. A cabinet company here used to sell poplar trim, and they used it to turn the green to yellow on poplar.

[Myk Rian]

Try oxalic acid to bleach the stains.
Bar Keepers Friend. Available in the cleaners aisle at your local grocery store.

Also good for removing rust from your tool tops.

[Joe Hillmann]

I just gave up on trying to prevent the black marks. They appear to have stopped getting bigger and once the surface of the wood drys no new black marks appear. So I will just hurry up and steam bend them all today and then let them dry. In a few months once they have fully dried I may try sanding out some of the worst stains.

So now my next question, will wet ash do the same thing? My options at the mill for wood that hadn't been run through the kiln yet were oak or ash, and from what I understand ash steam bends pretty well.

And as a side note I got one of the toboggans finished last night and I tried to put the majority of the black marks on the bottom of the sled with the idea that the bottom will be much easier to sand than the top.

[Howard Acheson]

Let me say that you want to avoid wood to metal contact as much as you can. The tannin in oak will always cause a stain. On something like a toboggan, there will always be moisture which is a key ingredient in the stain formation. In wet or high moisture applications, it's best to use a corrosion resistant metal. Stainless steel or brass fasteners are best.

[Mark Wooden]

ANY wet wood will get some degree of black/red/brown stain if it comes in contact with iron or steel- it's creating oxidation aka rust. Just wax your iron or sand- your choice.

Ash steam bends wonderfully, you won't want to ever bend anything else. I use it for making landing nets.

[Joe Hillmann]

ANY wet wood will get some degree of black/red/brown stain if it comes in contact with iron or steel- it's creating oxidation aka rust. Just wax your iron or sand- your choice.

Ash steam bends wonderfully, you won't want to ever bend anything else. I use it for making landing nets.

Since you have experience with steam bending do you have any helpful pointers? Or pictures of your work?


A few years ago I built another, larger toboggan out of ash but it had been kiln dried so bending it was quite a challenge. Since then I have built a couple boats out of steam bent oak and now these 6 toboggans. The best thing that I have found to prevent splitting on sharp bends it to make the bend with a leather belt holding tension on the back side of the slat being bent. By having the belt as a backing you can make your bends as tight as you want without fear of splitting.

[Mark Wooden]

From your post, sounds like you’ve done more than me. Surprising you’re just finding out about iron stains. I’d have to take a few pics of my net frames, haven’t made any in a few years and gave most away as gifts.

Keeping the outside of a bend under compression is very important. Make shaped cauls or use steel banding to clamp them. Leather works but gets loose when wet. You can get used banding free at a lumber yard or construction site, they bundle lumber with it. And it’s coated, so it doesn’t rust or stain quickly;) You can bolt angle iron to it to provide a place to clamp it.
I try to keep continuous grain running through the bend or if I can’t, I turn it to the inside.
I keep a spray bottle of hot water and glycerin (20:1) handy to spritz dry spots while I’m clamping up

These are a few good guides-
http://www.leevalley.com/us/wood/pag...,45867&p=45869 (http://www.leevalley.com/us/wood/page.aspx?c=&cat=1,45866,45867&p=45869)

http://www.austin7.org/Technical%20A...0Ash%20Frames/ (http://www.austin7.org/Technical%20Articles/Bending%20Ash%20Frames/)


Have fun.

[Joe Hillmann]

Mark,
That first link has a lot of good information and I haven't seen it before, thanks for posting it.

I guess I never had the problem with the wood staining this bad because the wood I have worked with in the past was air dried for some amount of time before working with it. The wood that I am making the sleds out of this time is soaking wet and frozen.

[Mr Mike Mills]

I have had luck with this stain remover working to get those black marks off. I get the mainly around where my bar clamps are touching when the glue is drying.

354551
I get this at Menards but it looks like Walmart may also carry it.