Can someone tell me if this is a crack?

[Brian Brown Custom]

It is O1 tool steel, I was sanding after heat treat and temper and noticed it. Not sure if it's a crack.

 

[razormaker]

Nothing definite here but look to see if it comes through on the other side. The other possible test, try to ring it like a bell or tuning fork. If it is cracked there should be a bad tone or vibration. Just a couple of ideas.

 

[mete]

Doesn't have the shape of a normal crack but certainly a surface defect wihich should be ground out .

 

[sykes3170]

Funny shape and place for a crack. Grind a little deeper and see if it goes away. It almost looks like some kind of contamination?

 

[Brian Brown Custom]

Thanks for the advice. It doesn't go through to the other side so I'll keep grinding till it disappears.

 

[stezann]

I have had similar surprises and i was very concerned...but it was only a superficial artifact.
To be sure, sand it and use a crack revelator spray to have a backup proof.

 

[Stacy E. Apelt - Bladesmith]

Details would help:
Steel type, hardened or not, forged or ground, source of steel?

It looks like an inclusion or other artifact. As said, try and grind it out.

 

[Ken H>]

Use a bit of dye (something like Prussian Blue) on it - if a crack wouldn't it tend to be a tad darker in crack where dye soaked in?

 

[Atlas Knife Company]

You could get it x-ray'd to be certain.

 

[Shaw Blades]

If its 52100 I'd say its a crack.

I've had some weird cracks like that before.