Burn marks on edge of purchased vintage chisels?

[scubadoo]

Hello,

I've just bought a few chisels on eBay, and the edges on a few have been freshly ground and have a black mark that kind of looks like a burn, not really sure.

Should I be worried about it? Could the temper be affected?

Cheers,

Dave

 

[Cheshirechappie]

It does sound suspiciously like someone has overheated the steel in grinding it. On new, clean steel, it would be a blue colour, possibly with a few other 'tempering colours' as well. With the oxidation stain on older chisels, the colour may not be as distinct.

All is not lost. Firstly, try honing an edge on the chisel and seeing how it lasts in normal use. If it doesn't last, grind past the coloured mark (taking care to keep the steel cool by either frequent dipping in water, or allowing it to cool between touches on the grinder), and then hone in the normal way. A wetstone grinder (if you have access to one) will allow you to grind the lot off in one hit - the water flow cools the tool edge.

It may not be the seller's fault. They may have sold the chisels in honest ignorance of what the marks meant. Or, possibly, they may have rather cynically put an edge on it not caring if they overheated the steel or not. There's no way of telling.

 

[TobyC]

Will it clean off easily? The person sharpening them may have used something to darken the surface while grinding, to look for high/low spots. Could be black marker or cold bluing etc. Sharpen and take for a test drive before doing anything else.

Toby

 

[Jacob]

Hello,

I've just bought a few chisels on eBay, and the edges on a few have been freshly ground and have a black mark that kind of looks like a burn, not really sure.

Should I be worried about it?

No. Ignore it.

Could the temper be affected?...

Yes, but so slightly you'd hardly notice. And anyway it will improve with subsequent sharpenings, but keep away from bench grinders!

 

[Cheshirechappie]

Was it you who sold those vintage chisels with grinder-burn, Jacob? Perhaps because you couldn't face the task of sharpening past the soft bits with an oilstone?

 

[Jacob]

Was it you who sold those vintage chisels with grinder-burn, Jacob? Perhaps because you couldn't face the task of sharpening past the soft bits with an oilstone?

I have over done it in the past but it only takes a quick hone to hide it! It just means you may have to sharpen sightly more often until it's gone, so it makes hardly any noticeable difference.

 

[GazPal]

Hello,

I've just bought a few chisels on eBay, and the edges on a few have been freshly ground and have a black mark that kind of looks like a burn, not really sure.

Should I be worried about it? Could the temper be affected?

Cheers,

Dave

Hi Dave,

The best way to find out if too much temper has been drawn from the edges is to put them to good use and any immediate problems will be highlighted by premature dulling of the burnt section of edge, but I'd not tend to worry unduly, because it's an easy fix via additional honing or a straight forward re-grind. Either way, it's not a serious problem.

In all honesty, it's pointless re-grinding or honing past the discoloured section of steel unless a problem exists.