Buffed Blade

[Thekirsh]

Hi Guys,

I was reading about the loss of hamon due to fire and it was mentioned that hamon can also be lost through buffing.

 

Has anyone ever seen this first hand, I find it difficult to believe that buffing would create enough heat to change the steels structure

 

Simon

[Veli]

Hi Simon,

 

The crystalline structure of carbon steel can be altered in very low temperatures http://en.wikipedia.org/wiki/Tempering. This also leads to color change of the alloy due to oxidation. Machine sanding or buffing are capable of raising the local temperature above 250 C.

 

The weirdest piece of advice I've ever got was that I should repair the hadaware on a nanbokucho tachi by TIG-welding...

 

BR, Veli

[moss]

Gidday all,

 

I know Simon is not talking about buffing his own blades but rather the fact that from time to time a buffed blade is offered for sale.

I guess he, like I wonders if this has been done is there any hope or just to keep walking.

Veli ,did the TIG work

 

Cheers Moss

[Veli]

I'd think that if there's traces of heavy oxidation (= color change to brown/blue) due to buffing, the temperature has been high enough to affect the crystal structure, and the blade may be badly damaged.

 

The guy who told me to hide kizu by welding was actually a teacher of metalworking in a local vocational school. I tried to explain about martensite and austenite, crystalline structure, hada, effect of thermal stress and gradient etc., but the guy just insisted that by selecting a correct filling alloy and by machining the welded surface it would be impossible to detect. I was so impressed by this person's resolution versus his expertise that I carefully padlocked my showcase and went to fetch some coffee... Hopefully this person never buys a real nihonto.

 

BR, Veli

[moss]

Thanks Veli,

I suppose in a case where clearly the colour has changed it is a write off,but in the case of no colour change can the structure have changed enough to destroy the hamon?

I am talking in a case of a potentially good blade that has had this treatment,would it be possible to have a polisher repair the damage.

Of course if one could be found who would work on it.

 

Cheers Moss

[Veli]

I actually tested machine sanding a blade... of a discarded Finnish puukko. I used a belt sander with a worn-down sanding belt. I tried to apply excessive pressure, but the temperature of the blade remained well below 100 deg C. The puukko blade had a cross-section area resembling that of a stout hira-zukuri wakizashi. Thus it seems that it takes excessive power, pressure and recklessness to increase the temperature above the safe limits for the hamon. Buffing with a stiff fabric work wheel rotating several krpm may be more dangerous in terms of temperature, however. As a conclusion, I'd estimate that the risk of damage deep in steel is not too large, provided that no color changes are visible.

 

N.B. (for those who have not read the whole story): This test was performed on a worthless modern knife in order to assess the thermal damage inflicted on previously mistreated blades. I'd like to stress that all forms of buffing, amateur polishing, sanding, machining etc. applied on a nihonto are equal to destroying cultural heritage.

 

BR, Veli

[moss]

Thanks again Veli,

 

Nice bit of information on the heat required to change the metallic structure of a blade.

I guess I won't dismiss a buffed blade if the cost is low,the only negative to one, is the cost to have it repolished .

 

Cheers Moss

[David Flynn]

Buffed blades may be polished. However, one should consider them like a rusted blade. Is the actual blade worth being polished? Fortunately, the buffed blades I have seen, have mostly been Showato.

[Thekirsh]

Thanks for the feed back Guys, especially Veli and his experiment.

 

I guess it gets back to each individual blade,light or heavy buffing, time buffed and type eg cloth or wire wheel.

 

And yes I think we have all seen examples of Showato blades that have been polished up a treat by pop before he handed it on to his eager grandson :D

 

Simon K

[loui]

I've polished several very badly buffed blades, no loss of temper and they turned out fine.

 

Regards,

 

Louis

[Jean]

I can confirm what said Louis, I had a a Kaga Shinto blade totally buffed, no lines (shinogi ...) no hamon, no hada .... It turns out with an ito suguha and a splendid masame hada.

[IanB]

All, I think I would distinguish between buffing and linishing. Despite Veli's experiment, I know the latter can generate a considerable amount of heat depending upon the speed of the belt and its grit size. Many years ago a guy found a couple of blades in a cellar whilst reading the house-owner's utility meter. On mentioning them to the owner he was invited to take them away for nothing. This gent then called me and asked if he could bring them to my place for an opinion. One of the blades, a large unsigned shinshinto katana with horimono, had no less than 5 hagiri (the other I cannot remember at all). I am convinced the damage was the result of the gent deciding to clean the blades up a bit before showing them to me using an industrial belt linisher. I do remember there was no heat colouration - just the 5 hagiri spaced almost equidistantly up the blade.

Ian Bottomley

[Tsugio Kawakami]

  IanB said:

All, I think I would distinguish between buffing and linishing. Despite Veli's experiment, I know the latter can generate a considerable amount of heat depending upon the speed of the belt and its grit size. Many years ago a guy found a couple of blades in a cellar whilst reading the house-owner's utility meter. On mentioning them to the owner he was invited to take them away for nothing. This gent then called me and asked if he could bring them to my place for an opinion. One of the blades, a large unsigned shinshinto katana with horimono, had no less than 5 hagiri (the other I cannot remember at all). I am convinced the damage was the result of the gent deciding to clean the blades up a bit before showing them to me using an industrial belt linisher. I do remember there was no heat colouration - just the 5 hagiri spaced almost equidistantly up the blade.

Ian Bottomley

 

Wouldn't the heating of a blade reduce the risk of hagire? It was always my understanding that hagire form from yaki-ire if the temperature change is too great (steel too hot, water too cold) or from impact/flex placing too much strain on overly stressed parts in the steel. Adding heat should draw back the hardness, making it softer and less likely to break, no?

[IanB]

Once the temperature had reach the point of decomposing the martensite, I would agree with you. However, I suspect that what caused the hagiri was the localised heating below this point causing localised expansion and the setting up of extreme stressing.

Ian