Staining whilst steam bending

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Staining whilst steam bending

Postby TonyH » Tue Jul 29, 2014 11:36 am

I steam bent some green ash chair parts yesterday. A set of turned rails for the back, and the back legs - shaved with drawknife and curved spokeshave.

Almost all went rather well, the only trouble I have is the presence of blue/black staining on the pieces after they come out of the steamer. This looks to me like the reaction of tannin in the wood with the steel from the tools, somehow "developed" during the warm wet steaming. It was not through contact with anything whilst in the steamer.

Although unsightly, it isn't very deep, and can mostly be removed by another working over with the spokeshave and a concave card scraper. Fortunately the back legs I had left slightly chunky to clean up after they were bent.

Do other people get this staining ? Is there any way of avoiding it, or is the clean up afterwards the best option ?
TonyH
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Re: Staining whilst steam bending

Postby ToneWood » Wed Jul 30, 2014 6:10 pm

Hi Tony, I bent some ash to make a saddler's clam and there was no tannin stain. Nor have I seen tannin stain on any of the ash I have worked for tool handles & shave/bowl horse legs. Is it possible that the wood is not ash but, say, sweet chestnut or some variety of oak, both of these woods contain tannin which will typically stain blue-black?

To clean tannin stains, mild acids seem to be the order of the day: you might want to try white vinegar first - failing that oxalic acid (sometimes sold as "wood bleach" or "wood bleacher"), for which it would be prudent to wear safety specs. & gloves - it is poisonous (found in rhubarb leaves) & corrosive. If you have trouble finding it locally, you can buy it cheaply as crystals off the internet (e.g. ebay & Amazon). It is also used for cleaning leather before it is dyed, by beekeepers and for cleaning alloy wheels, among other things. Typical recommended dilutions I have seen include: one teaspoon per pint of water or a table-spoon per quart (i.e. 2 pints) - although it can be used stronger.

More info. on oxalic acid here: http://www.ebay.co.uk/itm/500g-OXALIC-A ... 58a67c6691
e.g.
Prepare a solution by dissolving 60g of oxalic acid in 1 litre of water, apply to stain or rust and allow to work for 20-30 minutes. Always rinse thoroughly with clean water. For wood bleaching it is recommended to neutralize after treatment with a borax solution (3 tablespoons of borax dissolved in 1 litre of water).
BTW To clean the oxalic acid off leather, some use saddle soap, which is usually a little alkali.
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Re: Staining whilst steam bending

Postby TonyH » Thu Jul 31, 2014 10:44 pm

Thanks for the tip about oxalic acid.

It is definitely ash. But you have got me wondering now. My shave horse has red oak clamping parts, and the tool rest of my lathe is the same. The ash would have been in contact with oak, and I would have been handling oak and steel tools as I worked it. Could it have transferred from my hands ? It amazes me just how black my hands can become after working with oak. It was hot and sticky weather when I was working it.
TonyH
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Re: Staining whilst steam bending

Postby ToneWood » Fri Aug 01, 2014 9:43 pm

Yes, probably - I have got in the habit of washing my hands regularly in soapy water when working on bowls, especially near the end, so as not to mark/stain the surface. Is your red oak still green (!)? I thought red oak was a north American species (I had a red oak floor in one home) - are you in the USA/Canada?
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Re: Staining whilst steam bending

Postby TonyH » Mon Aug 04, 2014 11:41 am

Sorry - I've filled in my location now. I'm not in America ! I'm in Bedfordshire, but I'm also a member of the Wimpole group.

The red oak ... it is not green, but air dried. It comes from a timber supplier who deals with trees from garden or parkland, and planks and air dries them. A consequence of this is that his timber can be quirky and characterful; not the nice straight grain of forest grown trees, and quite often unusual species grown for ornamental value. The bits I used were cabinet making offcuts, which was what I had to hand when I needed a shave horse.

I did most of the shaping with a drawknife, but some bits (where the grain was awkward) with a concave spokeshave. I think these may be the worst affected bits, so maybe the iron is from the sole of the spokeshave. I think I' stick with the drawknife and leave them rougher and more oversized next time, leaving the spokeshave for cleaning up after they have been bent.
TonyH
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