What's causes this?

[Self Made Knives]

Earlier today, I was heat treating an air hardening steel and while I was waiting on the oven to go through it's cycles, I whipped up a file guide out of some left overs that were too small for anything else.

So, after daughter's basketball practice was over, I fired up the oven again and ran the same profile to harden the guide. Same kind of SS foil pouch as the blade earlier. Same wipe down with acetone. Same grit finish. The blade came out really clean, no air leaks at all. Perfect. But, why did the file guide come out like this:

It didn't really appear to have had an air leak, they were pretty clean. I quickly worried that it had somehow self tempered, but it hardened to 62rc, which is what I expected. It looks kind of cool, might leave it like this, just curious what's going on.

 

[shaun]

If you had any oily substance left over on them I will wager that would be your cause.However it looks very nice I would have just left them as is.

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[wall e]

Snafu custom? Looks like oily waves, is cool either way on whats the cause. Let me know if you get another set of scraps like that and see if we can make a trade.

 

[Rudy Joly]

It's just oxides from whatever you may have cleaned them with.
I do a fair amount of HT for other local makers and just for fun I found that soap and water gave me mostly a grey finish, acetone gives nice pinks and electric blues much like yours and mineral spirits give amazing purples and dark blues. I switch it up with every batch , the comments are usually that they think I anodized them. Think I'll try Prep-Sol next. ****Don't wrap your blades until they're well dried off, if not you may be in for a surprise. Safety first.

Rudy

 

[Self Made Knives]

Cool, I just never had this happen before, but then again, I'm still pretty new at this stuff. I did drill and tap the holes with thread cutting oil, so there may have been a tiny amount of oil still in the threads. But, since you've seen this before Rudy, I did wipe them down with acetone right before putting them in pouch. Must be it, still amazes me though. Tie dye filing guide.