Shirasaya - Should I stain or oil?

Hi Folk,

The wakizashi I recently received from Japan came in Shirasaya, as with so many swords the police registration / license was taped to the saya for many, many years. So long the glue from the tape had stained / soaked right into the wood. using alcohol wipes would not remove the marks, it even made the shirsaya look like it was made of 4 pieces of wood instead of 1.

I ended up lightly sanding the stains off. Should I sand the whole thing and tan / stain it with an appropriate product from the paint store (I'm guessing something like you might stain outdoor furniture with) or perhaps oiling it with something like Linseed oil (like we used to oil our cricket bats with)....

Or as one chap suggested just leave it alone now.... It just doesn't look even as I only sanded out the blemishes / stains

I'd send it someone who repairs these professionally if it's that much an issue to you.

Something you might try before sending it off to a sayashi. In finishing these shirasaya the Japanese do not use sandpaper. They use a variety of sawgrass or pampass grass called Tokusa to lightly scour the surface then powder it down with ibota.

If you have access to pampass grass then a bunched up wad of the leaves rubbed one way only and very lightly along the shirasaya may even out the surface colouration. I have used this with success on a shirasaya that was similarly stained by sticky tape glue which had also held the registration papers to the saya. Just be extremely careful and light handed. A little patience and care may be all it takes. If that fails then send it to a sayashi for refinishing.

A small caveat: It would be unwise to stain or oil the shirasaya. Firstly, it is not meant to be stained or oiled and secondly oil such as linseed would soak through the wood eventually and contaminate the blade chamber. Linseed oil is also chemically unsuitable for use in proximity to steel and if held in an enclosed space when freshly applied may ignite spontaneously due to a chemical reaction with oxygen that produces heat when drying.

Good for cricket bats and sometimes for bokken but not good (read tragic) for shirasaya.

Paint it with nothing! It should repatina in a few decades.

These are just pajamas for your sword. Something to protect it.

If the sword gets polished one day, it will need a new one anyway.

As long as the inside is good, your sword won't care.

Mark G

I am not sure that the inside of the shirasaya is in perfect state, there is some black rust on the blade

Jason,

Next time you have a question, ask it before you try the sandpaper. I'd rather answer, "What can I do about tape residue on my saya?" that the question you asked at the top of this thread.

By the way, linseed oil doesn't spontaneously combust; rags soaked in linseed oil spontaneously combust. The oil isn't especially flammable but the heat produced by the oil's oxidation will start a rag on fire.

I agree; don't put oil or stain or anything on the saya; have it fixed right if you want it fixed.

Grey

By the way, linseed oil doesn't spontaneously combust; rags soaked in linseed oil spontaneously combust. The oil isn't especially flammable but the heat produced by the oil's oxidation will start a rag on fire.

To expand on Grey's comment, linseed oil (and other oils such as tung oil) polymerise by reacting with oxygen. The reaction is also assisted by UV and heat. If it is in an enclosed space, it will use up the oxygen and the reaction will stop - it won't burst into flames. I've got a jar of home-made boiled linseed oil that always has a partial vacuum in it when you open it.

Mix linseed oil with cotton waste though and (this is the important bit) make a suitably large pile and you may, in time, have a small and exciting fire. The heat from the reaction can't escape, so it builds up until it causes a fire. OTOH, that won't happen if it is just one small piece of rag, because the heat of the reaction will dissipate.

It is almost certainly a bad idea to apply linseed oil (or any oil) to a saya. It is unlikely that it would seep through to the blade chamber if it is applied properly (i.e. thinly). It is more likely to set hard in the outer layers of the wood. It will however stop the wood from breathing - consequently any moisture inside the blade chamber will be unable to wick out through the wood. The result would be an increased chance of rusting.

Kevin

Thanks for the replies guys.

Jean: I don't think the shirasaya caused the black marking / rust...

It (shirasaya) doesn't look that bad as it is so I'll take the advice and refrain from oil and or stain / tan. Over a few years it should develop a nice patina......

Well whaddaya know... So thats what happened! when I was a kid in England I used to play cricket. I oiled my bat (like a good little cricketer) with linseed and left the rag soaked in the stuff on the bench in my dad's tool shed. The bench caught on fire or rather got scorched (Not too badly) I always thought it was the oil in the wood that burned but it was the oil on the rags that scorched the wood. (come to think of it, I cant recall having a cricket bat burst into flames). I think I have stated elsewhere that physics and/or chemistry is not a strength of mine. However, it just goes to show how you can perpetuate a mistaken theory..... Sorry If I mislead anyone. Thanks Grey, you cleared up a long standing misapprehension of mine. My Father was way too angry to explain it to me at the time, and I didnt dare bring up the subject ever again. :D

Keith

Just dug around in the chemistry. It appears that you generally need a compacted or very folded rag or paper and some contaminant (e.g. dirt, silica) to guarantee that boiled linseed oil will cause spontaneous combustion. The contaminants may further catalyse the oxidation., which is already catalysed by the driers that boiled linseed oil contains. From one individual's experiment, it looks like it takes something of the order of 7 hours to get the temperature up high enough, and even then it will only smoulder into a charred mass unless it gets enough air.

Apparently, according to the results, you can also get spontaneous combustion under those circumstances with safflower, walnut, avocado, canola and olive oils as long as you mix 0.3% of a 6% manganese drier with them. In fact you get a higher temperature rise with olive oil than you would with linseed oil (172C vs 148C according to one experiment). OTOH, raw linseed oil won't do a thing - the reaction is far too slow. Under some circumstances raw linseed oil can take decades to completely polymerise.

On the subject of stains, there's always the problem of how the volatile components will affect the steel. The volatile components could, I feel, migrate through the stained wood and might take some time to leave the wood completely, particularly if they'd migrated to the blade cavity. It's a case of "if in doubt, don't do it!" :-)

Kevin

Edited to add that cricket might be a more interesting game if the batsmen periodically burst into flame and had to do their runs trailing clouds of black smoke. :-) It might even beat Brian Johnson's "The batsman's Holding, the bowler's Willey." :D