Quote Originally Posted by clavichord View Post
Interesting, JimmiHAD! By the way I remember seeing some Sheffield razors marked "Tempered By Fahrenheit's Thermometer" on the blade or spine. I own one dating back to William IV (1830-1837) so I guess this was a quite new process in that time but maybe a not so rare practice since then.
It is interesting to me too. I find it a romantic notion (in a good way) that a smith could be expert enough to intuitively know when the steel was heated to the correct temperature by eye. I know that magnets can also contribute to the process but I think that is a small window IIRC.

Some of the old Sheffield wedges I have take a great edge and shave wonderfully smooth. So I imagine they got more blades right than wrong using the eyeball method and I bet it was a matter of pride for many of them where they didn't want to use the thermometer. Here is a timeline of the invention and development of the pyrometer. I couldn't find much on the history but it appears from what I did find that the early ones were rather primitive and probably not very useful for forging.

I was watching yet another show on the Samurai warriors that went into the forging of their swords. I don't know if they use pyrometers in modern times but certainly the antique swords were made without the pyrometer of thermometer technology and are said to be the pinnacle of the smith's art.