The time frame for both the writing and the compiling of the book of Proverbs fits, most likely, somewhere between the 10th and 6th centuries B.C. this time frame would place Solomon's life and writing within the historical backdrop of what is called the Iron Age. The Iron Age began for most of the world around the 13th and 12th centuries B.C. and lasted the next 12 or 13 centuries leading into the Medieval and Renaissance times. This section of history is referred to as the Iron Age because it was during this time that iron became the mineral of choice for metal working. The Iron Age was preceded by the Bronze Age. Iron replaced as the metal of choice, not because it was incredibly superior, but primarily because it was abundant in virtually every region of the ancient world.
Bronze comes from combining the elements copper and tin. Copper itself wsa also common for that time and thus easy to come by. Copper by itself, however, was far too soft to be of any real use as either a tool or a weapon. Once the copper was mixed with tin, the two combined to produce Bronze; a considerably stronger alloy. The problem was that tin was scarce and more expensive even than gold. So even though Bronze was much easier to work than iron, and iron wasn't significantly stronger, iron won out because of its shear abundance.
Iron presented its own set of problems. There was plenty to spare, but the melting point for ironis amazingly high. Bronze melts down and can be cast at around 1,083°C. The melting point for iron is around 1,535°C. A man hears that and responds with, "Well, make the fire hotter then!" Which certainly sounds like a resonable suggestion, but the problem was that no one at that time knew how. The hottest kilns (a kiln is a clay oven used for heating metal) of that time could only reach tempuratures of around 1,150°C. It would be some time before any bloomeries would exist able to produce enough heat to fully melt the iron ore through the use of a bellows. Until then the blacksmith of the day was limited to producing what was known as an iron bloom, and working it into wrought iron.
An iron bloom was simply a blob of hot iron, both softer adn more pliable for the forging process. Iron, because it could not be melted, could not be cast. The process for shaping the iron was known as forging or hot-hammering. The blacksmith would produce a bloom, and then he would hammer it over an anvil literally pounding out the impurities. This process would be repeated several times over, purifying and strengthening the metal with each pass. Being slightly more maleable while red hot, the blacksmith would do much to sharpen the weapon during the forging process. Once the sword was adequately shaped, the blacksmith would then begin to put the finishing touches on the blade. This process was referred to as cold-shaping. The blacksmith would use a large file to make the blade sharp by running the file across the edge. Both the hammer in the hot-hammering or forging process adn the large file in the cold-shaping process would have been made of iron at this point in history. So iron would have been used by the blacksmith to sharpen iron, just as Solomon describes in Proverbs 27:17.
So...what then was Solomon's point? Just as a blacksmith would take one piece of iron and use it to shape adn enhance and sharpen another piece of iron, God desires to take men and use them to shape and enhance and sharpen other men. Let us make ourselves available to God that He might use us to sharpen others, and let us always be open to the sharpening effect others might have upon us.
Could you imagine one piece of iron saying to another, "Who do you think you are? You are just another piece of iron. What makes you think you should or could make me better than I already am?" Sounds silly doesn't it. Yet I think that is how we respond to others who God might be trying to use to sharpen us. Let's not forget that the sword is sharpened by a hammer and a file, neither of which are very sharp themselves, but the blacksmith knows what he's doing...