Pitting or streaking in clay coated 1095

PIndelicato

PIndelicato

Joined
Sep 16, 2002
Messages
1,577
Hello,

I've done several etch/polish cycles with this blade, and it seems to have gradually developed a problem below the hamon. I'm not sure if it's pitting or something weird with the structure or composition of the steel. Has anyone ever seen anything like this and know what it is? Also, what can I do to fix it and prevent it in the future, if anything?

I've never seen this before, but have only a few hamons under my belt and this is the first time I've used 1095. The steel came from Kelly Cupples if that makes any difference.

These photos were 'worst cases', taken in lighting and at an angle that highlights the issue, it is not nearly as obvious in casual handling but it is noticeable if you look for it:



 
Paul, I've had it happen. In every case, it was from over-etching. I don't mean etching too long per cycle... I mean where I wasn't quite happy with the look of the hamon and would etch it just one more time. And it ends up being one time too many.

The only way to get rid of it (IME), is to sand it out. If it's not very deep, you might be able to get away with something like 1200X. If you've really opened up the steel and they're deep, then you'll have to go down quite a bit coarser.

That's if you don't want that look. Some guys like it. Personally, I don't care for it because you spend all this time trying to make a super clean blade, and IMHO that makes a blade look "dirty."

I wish there was some formula that let you know exactly how many times a blade could be etched/polished BEFORE it started doing that. After a while, I think you just get a little better feel for when to say, "Okay, I'm done--- no more etching!" :) LOL


FWIW- somebody might have a completely different answer for you, and prove me completely wrong. My answer is just based on my experience etching and polishing 1095, W1, and W2. :)
 
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I read the paper last year so I am going from memory. It seems the orientation of the crystal affects the rate that the etchant will dissolve the crystal. Since grain orientation is random, some of the grains will etch faster than others. Every time you etch, the same thing happens, so the pattern becomes more pronounced. The light areas would be where the etchant did not act as quickly and the dark areas would be where it etched more rapidly. When you polish the blade it seems that you are cleaning off the high spots. Also, different crystals probably etch at different rates. Austenite might etch differently than martensite. If you know what you are looking for, (I don't) the pattern might give you some clues about the grain pattern in your blade.

Disclaimer: I don't have the paper in front of me so if I messed something up please chime in.
 
Are you neutralizing the acid after the etch (ferric?). I don't think I've had this happen to me but thats what the blade finish look like, residual ferric.
 
Thanks Nick...I was actually leaning towards over polishing vs. over etching (I've etched it 4-6 times in dilute ferric for 10-15 seconds, but polished it a LOT.) Maybe that was more etching than this particular blade wanted, but I've not had issue with similar etching cycles in the past.

I was afraid sanding was the only answer. Unfortunately, I have already etched my mark thinking I was about done and it's not super deep, so I can't sand too much without wiping that out.

Bo, that sounds like a good description of what happens with etching in general, but I'm not sure how to apply that data to my problem here?

Mike...yes, I neutralize with Windex after the etch (and then follow up with a good rinse in water under the tap for good measure.)

thanks all, I appreciate the feedback!
 
At this point I was thinking more along the lines of future knives. If you can figure out (read the blade) what is happening with your grain structure, you can make adjustments to minimize the problem in the future. For example, if the high spots are due to RA, perhaps a faster quenchant or a cold treatment before temper? If it is due to the grain orientation of martensite, are you satisfied with the grain size? Perhaps additional grain refinement is in order.
Personally, I think you are at a point of diminishing returns so do your best to figure out what the problem is, how to correct it, finish this knife and move on to the next one.
 
I have seen similar things in steels with large carbides.
One reason that sanding belts are not used in doing final togi is that the theory is they will "pull out" hard carbides along and near the hamon, leaving behind pits. Hand working the edge with papers, finger stones, and polishing compounds, will polish the hard and soft together, leaving a frosty surface, not pits.

As mentioned, over etching can eat stuff out around carbides, making them easier to dislodge, and also etching deeper pits in the more soluble structures.
 
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