Scorching wood haft?

[will52100]

I've seen several axe makers that stick there hafts into there gas forge for a few seconds to scorch them, then hand sand smooth.  Supposedly it hardens and makes the wood a little more stable.

Any thoughts on this?  I normally make my hafts and handles from air dried straight grained hickory and really haven't had any issues.

[navasky]

It's mostly done for looks and can also make the wood a little grippier. I like to do it before I fit the head, my theory being that it dries out the wood, shrinking it, and letting you get the head on a bit tighter.

[Frosty]

Fire hardening is an ancient practice if you don't have something to make a spear, dart, arrow, etc. point with. I don't know how much affect a couple few seconds in the forge has. I've warmed handles with a quick pass or two through the dragon's breath so the TreWax would soak in better. I make my handles from straight grain clear cabinet grade hickory. Recently I've started using the shop toaster oven to warm them to wax.

I posted pics of my handles in another thread last night, the dark one was warmed in the dragon's breath, the other in the toaster oven. Either way they're plenty durable and grippy.

Frosty The Lucky.

[natenaaron]

It is for aesthetics and some say it helps with grip but they are wrong. Grip is aided by poly, wax, or skin oils and sweat.  It will allow wax to penetrate further, not because the wood is more accepting but the wax is warmed by the wood and more easily enters the cells. 

Scorching and sanding wood is a popular way of coloring and bringing out the grain in some traditional Asian cultures' wood crafts.  I have seen Japanese, and some Chinese pieces but mostly Korea.  A beautiful look, especially with a red grained wood. It does not harden the wood in one short pass through the fire. 

Heat will shrink the wood as it draws out the water and when heat is no longer applied the wood will eventually return to the ambient humidity.  this is why a drawer made in the winter gets stuck in the summer, and a joint fitted in the summer does not fit so perfectly in the winter.  A short pass through the fire will not shrink the wood enough to make any difference.  In a kiln environment the wood will emerge harder than wood that was air dried in much the same way a sponge is stiffer when it is allowed to dry, but this is not going to happen in the forge with a brief pass through.

Hardening is is done with green, or air dried wood (If I remember my archaeology), followed by repeated, slow heating, charring and polishing.

[ThomasPowers]

Down here I try to let "new" handles dry at least a year before using them as "kiln dried" isn't dry compared to "NM ambient"; after that I don't see a problem using them; though I do soak them with linseed oil after they are installed in a hammer.

[Kozzy]

The subject got me poking around regarding any science involved.  It appears that a simple scorch is mostly hooey but there are some specific applications where it helps.  Assuming that the subject is not drying the wood (which will make it "harder"), in certain cases the resins in the wood along with the addition of some carbon can chemically form a hard surface that was good for spear points.  You needed the right wood and the point was thrust into actual hot coals in several rounds, polishing in between.

I'm trying to find the whole paper to cite but apparently there were some archaeologists who did tests with digging points and flame hardening back in 1986.  The synopsis reads: "This paper presents the methods and results of experimentation with the "fire-hardening" of wood. Thirty digging stick replicas made from deciduous and coniferous wood species were variously heat treated and subjected to both hardness and abrasion tests. Standard hardness testing proved all samples to be adversely effected by exposure to fire, while tests of wear or abrasion produced contrary results. Explanations of the experiment's outcome are provided in terms of physical, chemical, and mechanical wood science."  

So, with everything perfect, you might get some abrasion resistance but not an improvement in actual hardness.

I'd sure like to read the rest to see the actual scientific explanation of the results.

One other point came up that might have some applicability--Wood rots and proper heating kills off the fungus and bacterias which promote that.  This implies that fire "hardening" might have had a secondary benefit on tools where you started your build with essentially green wood.  That "blued" wood might look keen but it's rotten and the rot progress needs to be stopped...with heat/fire as one way to do that.

I'll probably get boinked for saying it but I don't think the quick flame issue improves anything and the "look" of scorched wood only reminds me of the crap we used to build in Jr. High shop class, using flame "staining" because the teacher didn't want to worry about proper stains, chemicals, or drying times.  It seemed cool in 1976 but just seems cheesy to me when I see it done these days.  So many ways to bring out the real beauty of the wood--and fire staining isn't one of them.

[natenaaron]

Hardening is not really hardening as a smith sees it. This is how fire hardening was explained to me by experimental archaeologists

slow heat the piece to draw out the pitch plunge the point into the coals to form some carbon

polish the carbon pitch mix with a stone.  Seeing as how I was in the southwest the stone was a piece of fossilized river bead.  Whatever the stone was it needed to be very fine grained.

After polishing the process was started again.  This was done over and over until a suitable coating of pitch, carbon and stone particles was built up.

It makes sense that the points would be adversly affected b y the fire.  The coating would melt.  I wonder about the abrasion test.  Were they rubbing or digging in soils.  Way too many variables IMO but this is one of the reasons I walked away from the Archaeology world. 

IMO "fire staining" has it's place like all other wood finishing techniques. This video from 0-2:15 shows the traditional Korean method and the results.  It also gives a very good look at just how far the char penetrates.

[Smoggy]

Kozzy, I'm not a fan of flame grilled oak either.

[will52100]

Kinda what I thought about scorching the wood, not nearly long enough at heat to kiln dry the wood or collapse the cells.  I've been using straight grained hickory I had sawn into blanks about 10 years ago that have been sitting in the attic of my shop.  When I do a handle I get it shaped and fitted, then leave in the house with the AC for a couple of days.  And do a stain and boiled linseed oil finish.

[natenaaron]

5 hours ago, ThomasPowers said:

Down here I try to let "new" handles dry at least a year before using them as "kiln dried" isn't dry compared to "NM ambient"; after that I don't see a problem using them; though I do soak them with linseed oil after they are installed in a hammer.

I think we are lucky in this regard, except monsoon season.  I do zero wood working during monsoon season.  Our current humidity is 6%

[basher]

I scorch all of the handles of my hammers and axes (unless asked to do otherwise) I like the finish. scorch with oxy torch 0000wire wool and then ren wax is the best finish i have found deep chocolate brown. the scorching acts a lot like sand blasting differentially burning the grain in the wood bringing out texture.

 the reason I started doing is is because i found my "blacksmiths " hands always marked the clean white wood..........and I love the finish.