How did they temper knives 200 years ago?

[cotdt]

I have some really old knives that I still use and I was wondering how they were tempered, to get a sense of their history. They did not have toaster ovens back then did they?

 

[Phil Dwyer]

As I understand it, primarily by the color of the steel produced by the heat. Many folks still use similar methods. Once the steel is hardened, it is sanded to expose shiny metal, which makes it possible to "watch the colors run" when it is gently reheated. The piece is re-quenched when at the desired color. As I recall it progresses like this (hardest to softest temper): yellow to straw to brown to purple to blue.

I found an interesting read a by a wood carving fellow on making his tools that covers this more with a photo and a chart, http://www.thecarvingpath.net/forum/index.php?showtopic=945. I really enjoyed his photo of progressive grain sizes produced by various steel temperatures at the initial (pre-temper) quench.

 

[A C Richards]

Blacksmiths have been using varying methods to temper steel. One way I have seen in older books was using a box of sand on the forge. It was allowed to heat to the proper temp and the steel was placed in the sand. This is still used today by some smiths. The heating and quench was done in the forge and whatever type of quenchant they had available, usually water or brine. It really has not changed much, just different technology. As Phil pointed out, oxidizing color plays a big roll in older methods.

 

[Stacy E. Apelt - Bladesmith]

Many older, pre- electric days, knives were tempered by "drawing the temper". The knife was hardened, and after being cleaned up was tempered by one of several methods. It may have been briefly held over the coals to heat the spine, and the colors watched as they progressed up the blade toward the tip. The blade was plunged into water to stop the temper when a straw color was reached for knife blades, or a darker blue color for springs.

A hot sand box was also a standard device that allowed a longer temper. This was usually an iron box full of fine silica sand, that was placed on the forge,over the coals, to heat the sand to a desired temperature. The knife was buried in the sand when the temperature was right, and the air was shut off the the forge.

Another technique was setting the spine of the blade on a piece of hot iron, and watching the colors run. Many smiths still do this today to draw a softer spine.

I have heard of that early smiths doing production work (such as armorers) would use an oven somewhat like a bread baking oven to temper their steelwork in, they were similar to the tempering ovens used by glass blowers. Such ovens used the large stone mass to regulate the heat, and were carefully stoked to keep the heat at the desired temperature. As was the rule in that day and time, everything was done by eye and by feel. It took years of experience to gain that skill, and was a highly respected talent.

In Japan, the making of great swords and knives was only partly a product of great smithing. It was mainly a product of greatly talented smiths who understood the steel they were using and how to do the heat treatment. Secrets of heat treatment ( all part of yaki-iri) included the clay coating and timing of the quench to attain some degree of auto-tempering.

Stacy