STAMPED KNIVES: Most less-expensive knives are stamped from sheet steel and are lighter and thinner than forged knives. Stamping can produce a decent blade, but without the heaviness of a bolster larger stamped knives may feel flimsy and unstable when used to cut hard-surfaced foods such as watermelon.
FORGED KNIVES: Forged blades are made by heating crude steel to more than 2,000°F and shaping it with a mold and a hammer. The blade is then ground down, tempered, sharpened and finished off. Forging is a labor-intensive process, which is reflected in the cost of the knives.
BOLSTER: A sure sign of a forged knife is a bolster — a thick collar of metal between the blade and the handle. Manufacturers claim that the bolster adds weight and balance to the knife, but it also keeps the user's hand away from the blade, which makes the knife safer.
TANG: In a full-tang knife, the blade metal extends to the end of the handle. According to manufacturers who produce full-tang knives, this gives the knife more balance. The full tang is visible on wood handle knives; on synthetic handles, full tang would mean that the blade extends at least 60% of the way through the handle.
ROCKWELL HARDNESS SCALE: This is a progressive measurement in degrees used to rate the steel's hardness: from 52 for soft steel to 60 for high-carbon stainless steel.
CARBON STEEL: This is the oldest type of steel used for knives and is hardened at 53 degrees Rockwell. Carbon steel is easy to sharpen, but these knives will rust and stain.
STAINLESS STEEL: Stainless steel knives, first popular in the 1920s, resist rust and staining. The blade is 61 degrees Rockwell, which means that it's too hard to be sharpened on a steel and can only be sharpened professionally.
HIGH-CARBON STAINLESS STEEL: Most manufacturers now combine the positive characteristics of both of the above; high carbon makes the knives easier to sharpen while the stainless steel keeps them from getting stained and corroded. Every manufacturer has its own metal recipe with some containing molybdenum and vanadium steel. The specific combination determines how hard a blade is, how difficult it is to sharpen, and how long it will hold an edge. If a knife's Rockwell hardness is in the mid-50s, it should be easy to sharpen but still maintain a sharp edge.
MOLYBDENUM/VANADIUM: Molybdenum is added to the steel mix to counteract the brittleness that's in hard steels, and vanadium contributes a unique, microscopic grain that makes it possible to grind a very sharp edge.