Typically, Japanese chef's knives are available in two metals: stainless steel and carbon steel. Carbon steel blades take and hold an edge better than stainless steel ones, are easier to sharpen, and are generally less expensive, user JavaBean noted in recent talk on Chowhound. On the downside, carbon steel knives rust easily so they must be dried carefully after washing. They can even cause a chemical reaction that darkens the cut edge of pale, high-acid fruits and vegetables. But for some cooks, the reliably sharp edge you can get with carbon steel makes up for the fussy care.
There is a middle ground between stainless and carbon steel. Some knives feature a carbon steel blade clad in a stainless steel jacket. This cladding minimizes the potential for rust and reactions with acidic foods, since only the exposed edge of the blade is carbon steel.
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