Historically how did blade makers temper blades before modern ovens?

[Steelhog]

Fairly simple question - Historically how did blade makers temper blades before modern ovens or being able to hold controlled temps for over an hour? Thinking all the way from iron age to 1800s wondering how tempering occurred or the methods used if at all. Thanks all.

 

[DevinT]

Some would heat a block of steel or copper and then rest the spine of the blade on the heated block and run the tempering colors almost to the edge which would result in a softer spine and a harder edge.

Hoss

 

[john april]

the japanese swordsmiths passed the blade through the coals until the correct color appeared.

 

[HSC ///]

I’m going to guess flash Tempering similar to what John said above.
Or Measuring water droplets on the blade to a known time pattern

I flash temper now with a tempilstik marker

 

[A.McPherson]

I've also seen folks demo auto tempting a thick spined blade.
Edge quench from austenite temps, then quickly scrub the edge with steel wool to see the colors run up the blade. Then dunk into water when the desired colors are reached

 

[Stacy E. Apelt - Bladesmith]

By color mainly. The blade would be cleaned until the metal was shiny and then heated over coals or by placing on a hot bar of metal or stone slab. The temper colors would be watched and when they ran to the point desired, the blade would be immediately cooled in water. The color for a knife is light straw color.
This was often repeated several times to assure full tempering.

The charts are still in use for many industrial processes.

 

[PEU]

In this old video you can see how its hardened the usual way and then is tempered by the color using a hot rod as the heat source.

Pablo

 

[Tom Lewis]

My Wife's Grandfather was a blacksmith and he used the method A. McPherson described.

 

[weo]

In this old video you can see how its hardened the usual way and then is tempered by the color using a hot rod as the heat source.

Pablo

I never get tired of watching this video, thanks for the reminder.

Although, I wonder what Sir Albert would say if he were alive today. Plenty of craftsmen around...

 

[12345678910]

They used simple low alloy steels that didn't need hour long tempering.
re all the above methods that judge colour by eye.


gunsmiths would spring temper springs by putting the spring in a small container with oil.
The oil burned, naturally aspirated at a particular temperature for making springs (borownells shop kinks) That's too hot maybe 550F range
That goes aback to flintlock era, probably earlier


I saw a video originally on film, early 1900 somethings straight razors
they tempered in molten lead pot.
A wooden splint would stir the lead but not char the wood.
That would give you 450 F ish
I think they were dipped in graphite so as not to solder/tin the blade.

Molten salt bath of particular type melts at specific temps, depending on which salt.


How did my grannies bake bread ?
by eye and ear
Heavy mass cast iron stove, air control = heat control.
Experience, water drop bounce

bimetallic strip thermostats have been around a hundred years