Mortise chisels are used for heavy chopping mainly across the grain. The blade is narrow, thick and rigid. As the bevel angle is larger, they also can be used for levering out chunks - what you never should do with any other chisels.
Japanese mortise chisels are essentially made in the same way as Japanese chisels. The cutting edge is made of a hard steel which is forge welded to a softer stronger iron back. This method is grounded in tradition, and allows the use of very high quality steels in the smaller, artisanal, smithies which even today produce most high-quality Japanese chisels in their wide variety of forms and designs. Some smithies are familiar to Western woodworkers, but most market their tools only in Japan. This has meant that lately, in practice, some companies or brands have developed a good reputation in the West while others remain unknown, but this says little about the relative quality of the tools. Mostly one can say that among the Japanese chisel smiths, price is a very good indicator of quality. One difference is that some Japanese makers that market chisels in the West have often slightly modified their tools to better match Western expectations and working methods. For instance, traditionally, one must finish fitting the ferrule to the wooden handle, and mushroom the edges of the wood over to hold it in place, but now this is often done by the manufacturer. The smiths have also adjusted their products to the demand for a higher level of finish on the blades to reduce sharpening/tune-up time before their customers can use the chisels.
For ten years Fine Tools has been offering a very high quality line of chisels made by Master Matsumura with a cutting edge made of the finest "white paper steel" under the brand name Koshimitsu. So we are very happy to be able to add these robust mortise chisels or "mukoumachi-nomi" which are made to the same extraordinary standard, to our store. Like other Japanese chisels, these mortise chisels feature a hollow back, which greatly reduces the effort and time needed to flatten and hone the chisel's back. By the way - as one reworks the back of hollow-ground chisels, the flat edge also moves back into the hollow, so that with normal sharpening methods, you never loose the vital flat area on the rear side of the cutting edge.