NitreBlue Salts versus Steel Composition

[Drunken Marmot Forge]

I've been dunking damascus steel in NitreBlue for a week now, experimenting, and figured I'd see if other folks were willing to share their thoughts. With 15N20 and 1080 steels, I'm really just seeing the difference in the etching itself, not in the NB effect, but when CruForgeV is added to the mix, then I'm getting a nice color shift between the steels (15N20, 1080, and CruForgeV - I believe it's the 15N20 that is turning color first):

So my first thought is the tempering/oxide colors versus temperature is dependent on carbon content (since the CruForge should be a few points higher), but could be other elements alloyed in the mix... Unfortunately I've got limited steel on hand (and don't really want to throw any mild in the mix), so figured I'd see who else has experimented with this?

Currently have another gordian knot billet (CW twists 15N20/5160 and CCW twists 15N20/CruForgeV), that could give an interesting pattern if the carbon content is the main indicator for color... will post results of that once it's done.

Curious if folks have any favorite steels for NitreBluing as well...

Cheers,
David

 

[Drunken Marmot Forge]

Don't remember which steel is which (aside from the 15N20), but a little contrasting color came through in the gordian knot billet... the 15N20 seems to be the 'bluest' of them, so thinking the carbon content is not the primary indicator... have to see what other steels I've got laying around. Tempted to blue up some punches and chisels as well (S7) next time I fire up the salt pot.

 

[jdm61]

David, what is the temp on the nitre blue? My recollection is that they are much too hot to use on carbon steel blades.

 

[Drunken Marmot Forge]

I've got the salts at around 600F (IR thermometer works well for this and matches the thermocouple probe). The more recent threads here on BF suggest that a short dunk at around this temperature only causes minimal impact on performance. Ed Caffrey has some good posts on this elsewhere on the web as well, where 300F or so is the temp.

I'm not planning to use this on blades at the moment(although maybe something like clay could be used to create a non-blued hamon... or partial bake-on laquer), but on other hardware. At the moment I'm just trying to bring out contrasting colors on damascus bottle openers and really getting none with the standard 1080/15N20.

I got interested in this coloring after seeing Johan's website, and am trying to figure out some steel combinations that provide such contrast (and temps/time in salt bath), so both experimenting myself as well as reaching out in this thread to see if others were willing to share what's worked for them...

5160 and CruForgeV give slightly different colors in the 600F bath, and enough of a shift compared to 15N20 to provide a nice color contrast without etching the steels. I've also gotten a pale copper color from leaving 1080 in the bath a while at a little bit higher temperature, but haven't experimented too much beyond the gray-blue color range yet.

A203E is next on the list to try as the claim is that turns green at ?? temperature...

Cheers,
David

 

[Stacy E. Apelt - Bladesmith]

No opinion on steel mix, but a short dunk in 550-600F salts will make no harm to the blade edge.


Most people temper far too low anyway, in false thinking that it makes a sharper or harder knife. Most all properly hardened knife carbon steels temper to best performance in the 450F range. 300F tempers merely indicate that something else was compromised in the hardening. This is sometimes part of the method of quench, and intended, but most often due to poor heat control or lack of sufficient austenitization time.
A second reason a knife tempered at 300F ends up a good cutter with a durable edge is when the edge is actually re-tempered repeatedly in grinding by being heated by friction to temperatures in the 400-500F range. The whole blade doesn't have to get all that hot or the edge turn blue to have the edge greatly overheated,

 

[Drunken Marmot Forge]

Getting a bit of color shift between each of the steels, although the main shift is between the 15N20 and the two non-nickel steels (slight shift between the 5160 and CruForgeV). A gray ScotchBrite belt was used to finish them before bluing. Pretty happy with the middle pic, but think I'll stick with just 2 steels until I can find something else with a larger color shift:

And the first one again in sunlight:

 

[Drunken Marmot Forge]

and some more experimenting with longer soaks this afternoon, in the 10-30 minute range, still with the salts around 615F.

here's the results of blue and beyond for the three steels - the candy cane effect comes out much better.

not your usual tempering spectrum obviously... ranging from almost purple at the end, through copper, pale green, and yellowish tan and then to the blues. next try will be at higher salt temp...