2002-04-16 - 7:46 a.m.

Well, Anne asked about 'blueing', so it is Armoring 101 time!

Today's lesson: Metal Finishes/Rust Prevention or Fun with Torches

Blueing is a process of pre-oxidizing the surface of a metal to prevent rusting. This can be done chemically, via heating or a combination. I tend to prefer the heat method as I like the color achieved better. Basically, as you heat metal it moves through the colors of the rainbow as it heats up. If you stop heating when it is around the purple/blue line you get a nice color when you rapidly cool it with oil. (Just make sure you are in a ventilated area and wearing a respirator, as the fumes are noxious) The rapid cooling is known as quenching.

If you overheat, you will get more of a grey color. Chemical bluing, actually tends to provide a more brown coloration. The heat blueing can also be touched up a lot easier than the chemical. Just buff up the areas in question and heat up the areas that need it and feather into the surrounding areas to blend the color.

With respect to quenching, oil tends to cool slower than water. If you cool the metal too quickly, you might make the metal too brittle (although bluing temperatures really shouldn't be causing too much of a temper of the steel) For example, when tempering a sword or knife blade, you bring the metal up to a straw (yellowish) color and then quench it in oil or water to rapidly cool it. This forces the crystalline structure of the metal into a particular structure that is very strong, yet brittle. If you water quench, then you heat the metal up to around a blue color and let air cool, which relaxes some of the rigidity of the structure in a process known as annealing.

Annealing is also used in the forming process if you overwork a piece to soften it back up so you don't crack the metal. When you bang on cold metal with a hammer, you are actually hardening the metal by forcing its crystalline structure to align. Some amount is good. Too much is bad.

Well, that is probably enough rambling lesson for today....

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