Popcorn finish

[Roger Keagle]

I have a question, does any one kow how to do "Popcorn surface" as seen on many Japanese tools ?

[Glenn]

Roger, do you have any photos of the finish?

[Tyler Murch]

As I recently learned, it is probably the effect of spot carburization. When heating and heat treating in a coal or charcoal forge, the places on the steel that are in direct contact with the fuel carburize, and the places not in direct contact with the fuel decarburize. It's what SOME people MAY call a blister effect. There will be lots of small raised round dots varying in size. I've seen some probably 3/4 the diameter of a dime.

[Roger Keagle]

I believe Tyler is on the right track, all of what I have learned so far seems to point in this direction. Not sure is we can do the surface using Western alloys of steel...does any one know more ?
THis has been a great help so far, I will try and find a pic for example.

[HWooldridge]

Probably similar to what you see in color case hardening.

[Tyler Murch]

I no longer heat treat directly in contact with the fuel, so I can't tell you what steels it will definately work with, BUT, any steel will decarburize and carburize, thus it should work with any steel, BUT some steels are more resistant to decarb. I believe O-1 is one of them, off the top of my head.

[Roger Keagle]

First I know it is noting like case hardening, and I have done that. The surface is disrupted like it had been selectivly been burned away...still trying to find a good pic, that will help I think.

[Roger Keagle]

Found a fair shot of an old plane blade with the surface I an trying to make...


Japanese woodworking plane Tsunesaburo

[clark-kentski]

Looks like he used acid since even his touch marks are effected,or he tossed some metal filings on his anvil and worked the hot piece on top,easy enough to try!Then again maybe your thinking of a japan finish like you see on old binoculars and such thats like a black crinkle paint.

[skunkriv]

Not sure if this will give you what you want but I have seen a method of forge texturing demonstrated by George Dixon. He heats his piece in the forge and lets it scale real good then picks off spots of the scale with his fire pick and scales some more, picks some more, repeat and repeat and repeat..... His finished piece did not have as fine of texture as the piece you showed but if you carried it to an extreme (repeat, repeat etc.) I don't know.

This would involve some major grain growth in any tool steel which would require grain refining heat cycling for sure. George was using it for decorative pieces. Nice effect when the textured piece is stacked behind a pierced piece overlay.

I think I have seen him do this in both gas and coal forges. Am guessing it might be a little quicker and easier to control (see) in a coal forge heating the piece hard from underneath and leaving the top surface exposed to the air.