Blade Restoration

In order to see all of the activity in the sword's hamon and hada (temper and grain), the sword has to be in polish. Unlike most collectibles, it isn't wrong to polish a Japanese sword and restore it properly. In this respect, they are more like fine old oil paintings which get cleaned and repaired, than they are like fine old furniture on which the original surface is valued. Age patina on a Japanese sword is only valued on the tang (nakago) and this is the part that is never cleaned.
This is also where a good togishi will correct the lines, shape and features of the blade, and bring it close to what the original smith intended. Polishing a Japanese sword involves an incredibly complex routine which doesn't open up the surface grain, but allows the texture to be seen, and at the same time brings out all of the incredible activities in the steel. This is way to ultimately appreciate a Nihonto, and can only be seen properly when polishing has been done.
However, every time a sword is polished some of the sword is lost to the polishing stones. Eventually the skin steel will be gone, the less refined and coarser core steel will show through, and the sword's artistic, historic, and monetary value will suffer. For this reason, only a properly trained polisher should ever polish a sword. Proper training takes years of study, almost always in Japan; no one can learn to polish Japanese swords by reading books and watching videos. Amateur polishers remove too much of the skin and leave the sword with an improper polish, which will need to be redone properly, which will remove even more of the sword.
Japanese swords don't have to be polished to survive; there is nothing about the polish that protects the blade from corrosion. If you own a sword in reasonably OK old polish, there is nothing wrong in enjoying it as it is and preserving it. These is still a lot that can be enjoyed. Seek the correct advice before doing anything, and try and see a few swords in full polish so that you will know what is expected and what to look for.

Slow down Grasshopper. Pretty much every new collector wants to do this. But it is not always a good idea. A polish isn't necessary to preserve your sword; as long as any active red rust is stabilized, your sword will be just fine in its old polish with proper maintenance. Sharpening = polishing and polishing removes steel from the blade and too many polishes remove enough steel that the blade's core steel starts to show through, a serious and ugly defect. Beginners often don't know how to properly care for a blade in polish. A new polish is easily scratched or even rust spotted and before you know it, the blade needs a polish again. Old scabbards can contain grit that can scratch a newly polished sword, or talking over a blade can lead to tiny droplets of moisture on the blade which turn into rust spots very fast.
Beginners often make the mistake of having their sword polished by an improperly trained polisher, which can irreparably damage the sword. Also,remember that not all swords are worthy of a polish: retempered, tired (core steel showing), and badly defected swords will not be worth the cost of polish. Low to mediocre grade swords are often worth less than the cost of polish. There are many periods in Japanese history where swords were produced as fast as possible, with less care about aesthetics and more thought about producing functional weapons. It is a fact that age doesn't necessarily mean value. In these cases your money would be better spent on a more worthy sword (or books). Learning to distinguish between mass produced utilitarian blades and those worthy of polishing is a huge part of your studies, and this is where the advice of knowledgeable collectors is invaluable. Spending $2500 on a polish for a sword that will be worth $1500 afterwards only makes sense if the sword has sentimental value. Otherwise, the money is better spent on upgrading. Having koshirae (mounts) made for a sword is also a common desire of new collectors. While this will do no damage to the sword if done by a professional, it can put a serious dent in your wallet. When the time comes to sell (and it will, unless you plan to be buried with your sword) you will be lucky to recoup half of what you invest in koshirae. Other collectors want original "Samurai" koshirae, not something you put together. Rather than jumping in with polish and/or koshirae, you would be smart to take your time to study and learn. With experience you will be able to make informed decisions and spend your money more wisely. Also, your tastes will change. A few years from now you'll be glad you don't have way too much invested in something you want to sell.
•Who should I have polish my sword and how much can I expect to spend? In the west, especially in the United States, there are many polishers to choose from. I can count on one hand the number of polishers outside of Japan who have proper training. A poorly done polish can do significant damage to a sword, both artistically and monetarily. Put another way, the most expensive polish is often the one that costs the least. We can not over stress this point: Don't give your sword to an amateur polisher.
•How do you know if a polisher has proper training? Ask experienced collectors (here on NMB, for example) who they'd recommend. If the polisher lives outside of Japan and he advertises his services on ebay or someplace similar, you don't necessarily want him to touch your sword; the true polishers have more than enough work without advertising.
•What will this cost? Prices vary with the condition of the sword to be polished but a good rue of thumb is $100-120 per inch of cutting edge. You will also need shira-saya (plain wooden mounts) and possibly a new habaki. You won't be putting a newly polished blade back in its old mounts because the polish can be scratched by any grit that found its way inside the saya over the centuries. Shira-saya can cost a few hundred dollars and habaki, if necessary, at least $200 more. This isn't inexpensive, which is why you need to make sure your sword is worth the expense. A properly trained polisher will be glad to look at your sword and give you good advice.
•How do I know if my sword is worthy of a polish? If you have been advised by knowledgeable collectors or other experts that your sword might possibly be worth restoring, one way to find out for sure that doesn't cost an arm and a leg is to have a professional polisher open a "window" on your blade. This is a small area of the sword that is polished to see the actual workmanship, hada, hamon and hataraki and see if the blade exhibits quality workmanship. Most polishers will do a window or at least look at your blade and give you advice. The other way is to find a sword study group or sword show near you and get the advice of as many advanced collectors as possible. Online opinions are at the bottom of the reliability scale, as there is only a limited amount that can be determined from pictures, but if from advanced collectors, is better than no advice at all. The key is to ask, ask, ask...before doing. Then take some more time and think it over before you make up your mind.

Polishing a Japanese sword is a major undertaking. There are only a handful of fully trained and competent togishi outside of Japan, and links to them can be found in the links section.
There are many others inside Japan, but please note that for any polisher, the waiting period can be from 6 months up to several years.
Within Japan, the laws for importing a sword make it easier to go through a broker. This is someone who will handle the import paperwork and deal directly with the polisher. This comes at a fee which can be a few hundred dollars, but is well worth it to be able to successfully complete the transaction with a minimum of hassle.
Outside of Japan, expect a similar waiting period. The better the polisher, the longer the waiting period usually.
Polishing comes at a significant price. The rate is usually between $50 and $150 per inch of blade cutting length. This means that an average katana of 25" blade length can cost on average $2500 for a decent polish. Then you have to understand that a newly polished blade usually requires a new habaki and shirasaya. Old scabbards usually have built up dirt and grime inside them that can scratch a newly polished blade, and therefore a new resting scabbard is recommended. The change in blade dimensions after a polish also require a newly fitted blade collar (habaki) afterwards. This can be as simple or as intricate as the customer desires. Expect a basic habaki to be in the region of $300 and a shirasaya to be around $400-600. These prices are estimates, and will vary depending on who is doing the work.

This is a question that is often asked, and yet is almost impossible for anyone else to tell you. As can be seen above, polishing and restoring a Japanese sword is a major and costly undertaking. Spending $3000 restoring a sword that might be only worth $2500 after restoration doesn't make financial sense. On the other hand, for a good sword, the ability to be able to study it, learn from it, and appreciate it afterwards is reward enough for many people.
The first thing to decide is whether you have a decent sword or not. This cannot usually be seen merely from online photos or if it is badly out of polish. Fatal flaws can be hidden under rust, and the blade could be tired (worn down from repeated polishes)
The best thing to do is get it to a professional togishi who can open a window in the blade and see what the hada and hamon look like. This involves polishing a small part of the blade, and will allow the polisher to tell you if the steel is good and if the hamon looks good. With his advice, you can usually decide whether to proceeed or not.
The other way is to take it to a sword show or meeting near you. Although there isn't always access to these everywhere, in many countries there are sword appreciation groups and shows. Questions posted on a sword forum will usually tell you if there is a group, meeting or advanced collector near you.
It is usually not financially viable to have a sword polished merely to sell it. Adding the cost of the polish to the cost of the sword makes the end result fairly expensive. Unless you turn up a sword by a good smith for little money, you might ultimately lose money on the deal. In this case, it is best to sell the sword out of polish and let the future owner decide how to proceeed.
If the sword has been identified by experts to be by a big name smith or a very good piece, then it is recommended to have it restored, as the end result will be a sword that shows the smith's work as it was intended, and the blade should increase it's value accordingly. But this involves positive identification of the sword and its maker, preferably through a shinsa.
In some cases though, collectors will spend the money on a polish so that they can enjoy the piece and learn from it. There is no doubt that there is no better way to study Nihonto than to look at good swords, in polish. Little can be learned from a rusted and stained lump of steel. In some cases it is sufficient to just care for the sword and enjoy it for what it is, and leave the restoration up to future generations.
In the end...the question of "should I have it polished" comes down to your own finances and how dedicated you are to preserving the blade. Cheap polishes by amateur togishi remove metal and shorten the life of the sword. They should be avoided at all costs.
Self-study will assist you in judging the shape and style of a blade, and perhaps allow you to see something under the rust and grime that indicates the blade has potential. Feel free to ask for opinions on the internet forums, but take the replies as a guide only, and try and have the blade evaluated in hand by someone qualified.
Accept the fact that during the polishing process, fatal flaws or blisters or open grain can become visible that were otherwise invisible. This is one of the risks that come with this hobby. On the other hand, there is nothing as satisfying as seeing a blade that has come back from the polisher in all its glory, showing wonderful grain and a temperline that shows everything as the original smith intended. This is what collecting is all about.
So in conclusion, there is no fast and easy answer to the question of whether you should have a sword polished or not. If money is no object, then yes. If you are like the rest of us, you will want to take your time, get other opinions and weigh the financial outlay vs what you will gain afterwards before you decide.

One of the really import things to understand when considering iron and steel is what rust is and how it works…a really simplified set of rules is that there are different types of rust to consider: There is stable rust, and unstable rust…your aim is prevent any rust ,or if you have rust to make sure it’s only stable rust.
 

Red rust..this is bad rust. It’s essentially active destruction and if not managed will destroy the iron/steel item. It’s Hydrated oxide Fe2O3•H2O (high oxygen/water exposure) with another contaminant such as salt. It is a sign that the environment itself is very corrosive, and is usually uniform….The classic example is an unprotected iron tool left in a garden shed.
 

Yellow rust. This is bad rust rust from iron oxides that is very soluble and is created in high water environments…a bike left out in the rain will form this yellow rust. Iron oxide-hydroxide FeO(OH)H2O (high moisture) It will run and will have run marks.
 

Brown rust..another bad rust. This forms in low moisture, high oxygen environments..Oxide Fe2O3 (high oxygen/low moisture). This is the sort of rust that an unprotected iron object will form in a family home. It tends to be spotty and will be propagated by contamination on the iron ( from a finger print etc).
 

Now we have good rust…BLACK rust…This is rust that forms in a low oxygen and low moisture environment, Iron (II)oxide – Fe3O4, also called magnetite.

It tends to take longer to form than other rusts and can actually form as a layer under other rusts, especially brown rust. Now the great thing about black rust is that it is stable and does not propagate. But more than that, it forms a layer that protects against active rust types ( red, yellow and brown)…for old artifacts made of  iron and steel ( swords and other weapons ) black rust can be a savior and preservative…very old European swords will often be covered in a coat of black rust and you do NOT EVER remove this black rust from these artifacts ( unless you are a philistine) as it’s the patina of age and authenticity and protection all in one. Japanese swords are a bit different in that the collectors aim to have the blade in polish and free of any rust ( to see and study the steel) but even Japanese swords preserve that black rust on the tang ( again to show the age )
The act of collecting and and appreciating Japanese swords is actually a bit of destructive process to gain access to the steel in the polished state  (no other area actively removes metal from artifacts…as a collector of old stuff it took me a while to get my head around the Japanese sword collection paradigm).

So with a blade that you are not going to likely get polished by a professional polisher, your best bet may be to follow a more European sword collecting approach which is to stabilize and protect only, until you can get an expert opinion on the worth of polishing.

So your aim is to stop the red, yellow, brown rust and stabilize to only having black rust. The way you do this, is to remove oxygen and moisture..so first oil…second oil and third oil. A good machine oil is best, such as sewing machine oil ( I use singers sewing machine oil. It’s cheap and easy to get hold of) If it’s heavily red rusted, I tend to actually give it thick layer of oil for a good few days…this really helps the oil penetrate the rust…carefully cleaning  with good quality lint free cotton cloth and 99% ethanol …then it’s a case of thin layers of oil and clean every few days. After a while you should have nothing left but black rust…then it’s just maintaining protection which is a very light ( no beading) layer of oil and  leave that black rust well alone unless your sending it to a polisher. Resist using acids and rust stabilizers on Japanese swords or any historic artifact for that matter
 

By Jonathan Davies