Timber and the risk of it causing corrosion

I didn't wish to hijack a thread, so started this. There's a lot of 'traditional knowledge' around in long-established trades, crafts, etc., and it's perpetuated by constant repetition and 'teaching', but a lot of it is little more than dogma: it hasn't been scientifically evaluated.

Oak is often demonised as being the wrong timber to use for instrument cases or tool cabinets, because it causes terrible corrosion of the contents. It's explained that it's the tannins that are responsible - or is it the acids, and if so, which acid*? Sometimes oak boxes are a problem, however oak is commonly used for this purpose, without any problem. In fact it may be one of the best options. So, it seems that oak can be very risky, or hardly risky. Why?

All(?) is revealed here:

**LINK**

* acetic, actually

Interesting! No source credited though?

The paper does say oak is one of the most corrosive of woods - and by acetic not tannic acid - but there are many ifs and buts.

In the past this has been discussed at length on this forum with references to a number of scholarly papers. In other words this has been extensively researched by museums, the timber industry and others.

In essence all timber is corrosive to some metals including mild steel. The corrosion is due to acetic acid.

A very late at night post which I generally avoid,

JA

Edited By JA on 03/04/2023 23:10:00

National Physical Laboratory. Can't get much better than that... I had hoped that the URL would reveal itself in my post, but I presumably did something wrong <sigh>.. (Like others, I like to see links spelled out as plain text in posts).

My reading is that, after some (unknowable) time, oak's liberation of acetic acid will drop to an insignificant level, rendering it 'safe'. Still seems risky to use wood, though...

JA I hadn't realised this topic had been done to death already...

Tannic acid in oak hence the "tannins" and why oak bark is used in the leather tanning process.

Drying the wood will reduce the acid contents effect, anyone who has worked "green oak" will know it turns your tools black very quickly and will also as mark as quickly if left in contact with iron or steel for a shot time. Takes a lot longer to see that on kiln dried material but get it moist again and the acid will become more active. link

Edited By JasonB on 04/04/2023 07:25:47

.

Thusly : **LINK**

http://resource.npl.co.uk/docs/science_technology/materials/life_management_of_materials/publications/online_guides/pdf/corrosion_of_metals_by_wood.pdf

Thanks for sharing it Kiwi Bloke

MichaelG.

.

Note: Nigel could presumably have done what I did

Edited By Michael Gilligan on 04/04/2023 08:13:12

As JasonB says, kiln dried oak later becomes damper, the acid is reactivated. Also, comments about the sapwood making steel tools black and the youngest wood, the bark, being used for tanning. I think that if heartwood, which is many previous years growth, already drying out in the tree is rather more benign, it suggests that the acidic effect slowly degenerates with age. Only the bark and sapwood of any tree species is the living part and the heart wood is dead.

Any potential problem could be overcome by putting VPI paper in an oak box/toolmakers cabinet, to prevent rust forming.

John

Did you read the paper, particularly section 2.3? Clearly, it's a rather complicated subject...

Dare I suggest Model Engineers are often naive about materials, tending to believe family names refer to one thing, or are all much the same. No so, there are thousands of different 'steels', over a hundred 'Brasses', and dozens of 'Bronzes'.

In this case there's a isn't a single wood called 'Oak'. Instead there are over 500 members of the oak family, plus a number of woods called 'oak', that aren't Oak at all. As plants have adapted over millions of years to their environment, it should be no surprise that English Oak is not identical to Asiatic or American Oak. Thus some oak woods are far less corrosive than others. The simple answer is making a tool cabinet out of the wrong type of oak will lead to tears.

Tool storage is a broad subject. Steel toolboxes are strong but - unless air-tight or lined - they don't protect well against corrosion because steel is a poor insulator, which encourages condensation. Wood is a good insulator, but it decays and is likely to emit corrosive chemicals. Also risky to use treated wood, because the nasty chemicals used to slow down decay can be corrosive. How fast wood decays depends on the circumstances - wood is vulnerable to damp, insects, fungi and bacteria. How it was seasoned matters too - slow dried wood is more stable in the long term than fast kiln-dried wood.

Bottom line: if a box is made to protect steel instruments, the builder needs to select an appropriate material, not just guess! Or combine materials to improve performance. For example, I have steel drawer tool-boxes in my rather inhospitable main workshop, but these are lined to improve insulation, and delicate tools are boxed in cardboard plastic containers as well, often with vapour paper, or lightly oiled. Inside the house, I have another workroom mainly for electronics. It's much more civilised, no oil at all, and a nice oak tool cabinet would sit nicely in it. Actually, most of my indoor storage is steel framed plastic drawers, with bigger tools hung on the wall. The room provides the necessary protection.

My feeling is that oak cabinets are most suitable for tidy indoor set-ups, fine work like clock-making, not my crude brand of shed-style metal hacking!

Dave

I’ve seen the results of storing tools in wooden boxes, so I store many of my smaller items in clip lock food boxes. I’ve had one very damp and one quite damp garage workshops and not suffered any rust on items stored this way.

Yes and it may be so for the acid they mention but the usual one in oak is Tannic acid, if you read my link you will see it's full name is Quertannic acid and we all know the latin for Oak is Quercus. Here is another link saying it's effects can be reduced by drying, 

Edited By JasonB on 04/04/2023 12:16:16

Does anyone know what wood Starrett used for their carved from solid micrometer, vernier et al cases.

Looks to me that the ones I have might be sapele.

Whatever it is simply carving out recesses in the solid material seems perfectly satisfactory from the corrosion point go view. I have some such cases and contents that I know to be over 40 years old. Not necessarily carefully stored indoors before I got them either.

Clive

Out of interest I have made boxes from all sorts of wood including oak but because of the story of corrosion I always seal all of my boxes with cellulose sanding sealer and let it go off for week or two or till the smell disappears which proves it is properly dry and then sometimes glue in felt liners or inserts using UHU general adhesive which can attack steels unless left to dry properly again till the smell has gone. I have got some really old beech at the moment (ex school) which is about 60 years old so that should keep me box making for a while. Just another point PVA based glues are corrosive for quite a while after they have hardened.

There certainly is a lot of "traditional" wisdom (aka folklore) that the tannin in oak can cause corrosion of steel tools, but that the tendency can be neutralised by "fuming" in an ammonia rich atmosphere. There was plenty of oak, but never mahogany, tool chests in the cold and damp satanic mills of Clydeside, usually where the more sophisticated work was done. Quality tool chests might well have been "fumed" but are the cheap imports? I have seen a mahogany chest on sale at an antique fair - it was alleged to have been the property of a clock maker. The same stall was also offering a wrongly assembled Pultra. When I asked (tongue in cheek) what it was, I was told £350, which probably speaks to the knowledge of the stall-holder.

Dick

In the case of the first link the National Physical Laboratory refers to American species such as White Oak. Doing anything suggested in that paper with English Oak will give you a big blue/black stain from the steel and if left there it will rust away.

I made a 'box' for taps by milling grooves in mahogany blocks about 20+ years ago. Not rusted yet...

YMMV!

Neil

My best boxes for instruments are made from cedar. That wood has better rot proofing than most other woods because of its natural oil content, which may also help when housing steel parts.

I believe it was my comment that sparked this debate so I'll give my two pence.

I have a couple of boxes I made from kiln dried English oak which I finished with danish oil and wax, they are lined with felt. I have never had any problems. But then I also keep my tools well oiled and sometimes in plastic bags within the box. I had heard the rusting rumours prior to making the boxes but figured if it was good enough for the countless manufacturers of engineers tool chests it would be good enough for me too.

Far far worse is tools wrapped in paper or stored in cardboard boxes, I have seen hundreds of tools ruined this way. Paper holds moisture. Don't do it.

The majority of my best tools are oiled and stored in thick plastic ziplock bags, I believe this negates the choice of container somewhat.

Why do you think that? I'd have thought that the NPL would have considered quercus robur their 'default' oak.

At the risk of flogging a moribund nag, like I said, it's complicated... And there's a lot of misinformation being perpetuated.

Timber is largely composed of cellulose, a polysaccharide, and some of its sugar units are acetylated. These can react with water to produce free acetic acid. Timber is consequently acidic, some more than others: oak, sweet chestnut, western red cedar and Douglas fir are particularly acidic. Acetic acid is volatile, so a closed wooden box, with timber containing any water, is very likely to contain acetic acid vapour, and this will corrode the contents. This is a risk for many metals, including, perhaps surprisingly, lead, not just Fe-based materials.

Corrosion can also occur by contact with the timber surface, and this appears to be a particular problem with tannin-rich timbers, such as the oaks. The corrosion is caused by acetic acid, not the tannins. Acetic acid is a stronger acid than tannic acid. Nomenclature is often muddled in source material: quercitannic (sic) acid is a tannic acid found in oak. There are other tannic acids, and tannic acids are a sub-set of the tannins.

Tannins are a major component of some 'rust stabilisers', the ones which don't remove the corrosion, but turn it black: the red rust is converted into black tannate, which protects the substrate from further rusting. Tannates are also oxygen scavengers, but I don't think this attribute is important here. However, what this means is that, (if there's moisture around), steel in contact with oak may develop characteristic black corrosion damage. Tannins are not volatile, so this blackening shouldn't occur without contact. Tannins will also cause dark blue discoloration of non-corroded metal. The timber may also be stained around steel fasteners, for example, which will also corrode. Again, it is the acetic acid that causes the corrosion, but the tannins that turn the rust black. I suppose that when tools rust in association with other types of timber, it's generally thought to be 'ordinary', moisture-induced corrosion, and the contribution of acetic acid is not appreciated.

Bottom line: all timber is suspect if there's moisture about; keep things dry, sealed from any acid vapour emanating from the timber, and out of contact with the timber, particularly if it's a tannin-rich timber. Closed boxes are bad, boxes sealed in plastic bags are worse. Now that there are alternatives, perhaps timber storage boxes, drawers, etc. should be avoided.