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San Mai ?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by 3fifty7, Mar 13, 2018.

  1. 3fifty7

    3fifty7 Gold Member Basic Member Gold Member

    Dec 24, 2016
    These are my first attempts at making San Mai billets as well as my first hidden tang knives. So as usual I'm flying on a wing and a prayer.
    The larger is a 15n20 jacket with 1084 core. The smaller is 1084 jacket with a 15n20 core. Pre heat treat I finished to a 220 grit then post heat treat and temper I brought them up to 600 grit with gator belts on my grinder. They both were etched in 4:1 ferric for two 2 minute cycles then sprayed with windex. I rubbed them with my fingers and a paper towel. This is where I am currently at. Now how do I get the 15n20 to pop?
    I've read many threads where people state they pull it out the etch, windex it and done. I also have read with Damascus, most will lightly sand or polish only hitting the 15n20 layers as they were less effected by the etch.
    What's the next step in my case? Buff? Hand polish ? Polish only the 15n20 ?
    Read more, reread until I understand because it's been asked and answered too many times before ?

    kuraki, john april and Hengelo_77 like this.
  2. 3fifty7

    3fifty7 Gold Member Basic Member Gold Member

    Dec 24, 2016
    Double post.
    Last edited: Mar 14, 2018
  3. kuraki

    kuraki Fimbulvetr Knifeworks Knifemaker / Craftsman / Service Provider

    Jun 17, 2016
    If you want it to really pop out, like black and white, you'll have to hand sand it in a way that you can repeat after the etch, that only hits the 15N20 after the etch. This is relatively easy to do with a damascus pattern because the constant interruptions allow the paper to float over the 10xx valleys and only hit the 15N20 peaks.

    On something like your top blade, the easiest way to do it is to have good flat grinds, and a stiff flat sanding backer that will keep the paper off the core. On something like your bottom blade, it's just really tough because the core is such a small surface area.

    I would bring them to a higher finish, 6 or 800 grit, and then sand with 1200 after the etch- it does not take very much so be careful and consistent about it. If you brush off some of the black you wanted to keep on your core, do it again until the dimensional difference is sufficient that you only sand the cladding.

    If you don't want quite "black and white" still take it to a higher grit before etching and then buff it with a paper towel by hand with wd40 or some other light oil. You'll buff away a lot of the darkness of the 15N20. More than you would think.

    They both look very well done BTW. Great work.
    Jesse Smith, valknut and 3fifty7 like this.
  4. Tom Lewis

    Tom Lewis

    Feb 24, 2000
    Nice looking blades.
  5. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Looks like a good job.
    To take it to the next step, use five layers on each side of the core. Say a 1/4" core of 1095 with five alternating .060 15N20 and O-on the sides. When welded up and forged down it makes a great look called suminagashi.
    You can use up to 20 side layers to get varying fineness of the san-mai pattern. Also, using 15N20 and low alloy steel like 1030 gives a different look.
    Finally, for a dark edge and light sides - layering 1/4" 203E and a core of 52100 orn1095 makes a nice sam-mai. The 203E is a very low carbon steel with 2% nickel and stays pretty white in the etch.

    On your current question:
    Another easy way to get a differential coloring is to decide which you want lighter ans which you want darker and put an etch resist on. In most cases, the edge will be the lighter and the bevels darker. Sand and finish as normal taking it to the desired finish grit. De-grease the balde well with acetone followed by denatured alcohol. Use a wide tip Sharpie marker to mask of the edge right up to the san-mai line. Etch as needed to get the bevels dark. Lightly hand buff the bevels if needed. Clean off the black Sharpie with alcohol. Wash well with Windex to remove any acid remnants drom the etch, and you are done.

    The same technique can be used to leave a smooth oval on a damascus blade for your logo to be electro-etched after the blade is etched and finished.
    Last edited: Mar 15, 2018
    olymon and 3fifty7 like this.
  6. 3fifty7

    3fifty7 Gold Member Basic Member Gold Member

    Dec 24, 2016
    Thanks for the compliments and advice.
  7. erik markman

    erik markman KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Aug 13, 2007
    Sand to 1000 or 1200. Etch in ferric. Buff. Etch in instant coffee.
    It will give you black and white.

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