It has to be said that I’m a big fan of Japanese tools and have been for many years, in particular their chisels. They are, compared to their western counterparts, a ‘learning curve’ and don’t suffer fools or unwarranted abuse gladly. The reason is that the blades are composite, being made from a super hard cutting steel and a much softer backing iron, which provides the chisel with the necessary flexibility for use at the bench on a daily basis. Centuries ago and even today, Samurai swords are made in a similar way; a softer iron core onto which is forged the much harder cutting edge. Were you able import a finished sword made from the blade in the picture, you’d need to speak very nicely to your bank manager to the tune of around £35,000!
The very hard (often around RC65) cutting steel is always forged, resulting in a close grained molecular structure enabling an unbelievably sharp edge to be obtained.
Like most good things in this world, there’s a downside and that is that the hard cutting edge is extremely brittle; much more so than a western chisel. If a Japanese chisel is used to lever out waste, it’s almost certain to result in a chipped edge which means extensive work at the sharpening bench to restore it.
One other glaring difference between a western and Japanese chisel is that the back has a long depression ground into it and it’s there for a very good reason. The back of a Japanese chisel still needs to be flattened and even more so if there’s a slight bump just behind the cutting edge. The depression or ura* (arrowed) reduces this area of very hard steel in contact with the sharpening medium and thus reduces the time taken to work on the back.
Were there to be no ura (as in a western chisel) the unfortunate owner would be standing at the sharpening station for a very, very long time as one of our customers, a Mr Mark Ayers, in his 5-star review of our Oire Nomi chisels probably found out!
It can also be seen from the same chisel that the distance from the cutting edge to the start of the ura (arrowed) is around 0.5mm, which is not very much.
After repeated honing, the edge will move backwards and begin to eat into the ura and so the ura from time to time must also be moved backwards by flattening the back on waterstones or another sharpening medium.
They do eventually, after much use, also turn into butt chisels.