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WEIRD: "Bull Thistle" Sharpening Stone Sparks

Discussion in 'Maintenance, Tinkering & Embellishment' started by FortyTwoBlades, Mar 28, 2017.

  1. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    I accidentally discovered something interesting about our Bull Thistle series of sharpening stones--they spark when you grind them into another abrasive surface! Or perhaps "spark" isn't quite the right word...they GLOW, almost like hot steel. No clue how it's doing that, or if the "sparks" are even hot or just luminescence of some kind, but it's pretty neat!

    [video=youtube;V_negIuWVSw]https://www.youtube.com/watch?v=V_negIuWVSw&feature=youtu.be[/video]
     
  2. Jason B.

    Jason B. KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jun 13, 2007
    That was oddly satisfying...
     
  3. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    For reference, it's normal to see sparks when mechanically abrading a bonded abrasive, but doing so on camera showed the nature of that spark in a more sustained way than manual scraping. However, it's definitely not typical to see such sparks when hand-rubbing the edges of a stone, and that's what surprised me! :eek:
     
  4. HeavyHanded

    HeavyHanded

    Jun 4, 2010
    They're freakin magic!

    Very cool, the field sharpening stone that doubles as a fire-starter.

    Benchstone please!
     
  5. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    Looks as though this is most likely a case of what's known as "triboluminescence", which is a little-understood phenomenon materials scientists are still trying to figure out. It's light emissions formed by the fracture or rubbing of materials, like the famous example of biting a wintergreen Lifesaver candy in the dark. The first known recorded observation of this was by Sir Francis Bacon, who described how it was a known occurrence for hard sugar to flash when scraped or nipped (from the loaves it was made in back then) in low light. Generally, very good quality crystals are needed to noticeably produce the effect, and larger ones will give off a greater spark, so between the premium nature of the synthetic ruby grains and the fact that it's a coarse 120 ANSI, it's able to luminesce with fairly low manual pressure. Neato! :D
     
  6. bucketstove

    bucketstove

    Sep 23, 2014
    Hi,
    is the belt diamond belt? Or does the pink bullthisle also contain traces of diamond?

    My guess is since its pink because of trace levels of Chromium(III) oxide then its glowing because of a chromium oxide thermite reaction..
     
  7. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    The belt is an old worn out 3M Cubitron. The stone is pink because the Bull Thistle series is made from synthetic ruby, which is aluminum oxide + chromium. Diamond is only present in the American Mutt stone (used in the manual demonstration) in low levels. The stone will similarly luminesce when struck with a piece of steel, which is a common test for triboluminescence.
     
  8. Rey HRH

    Rey HRH

    860
    Oct 6, 2014
    Is there magnesium or titanium in the stones? I know hitting a titanium driver on the ground can sometimes cause sparks.

    At least, you're not inviting people one by one into a closet to show the sparks.
     
  9. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    As noted in the post above, I've narrowed the phenomenon down to triboluminescence of the ruby grit. No magnesium or titanium involved. :)
     
  10. I was thinking along similar lines. Years ago, I'd noticed a Ti driver of mine throwing sparks when striking range balls at night; usually older, well-worn ones with a lot of embedded dirt/grit in their surface.

    At any rate, the pink glow from the stone is pretty darned cool. I could see that being a selling point as well. ;)


    David
     
  11. willc

    willc Gold Member Gold Member

    Aug 13, 2013
    I got my Bull Thistle stone a couple weeks ago and eased the edges on an old stone and didn't notice anything but after seeing the video I tried it again and I could get the glow when I passed the edge on an old diamond stone.

    This is a very cool effect.
    The stone is a great cutter too and so far I've got some nice edges on a few machetes so far.
    A bench stone in this material would be awesome.
     
  12. DavidHoback

    DavidHoback If you see me posting, remind me to STFU & leave.

    326
    Dec 10, 2014
    Are you sure it's not just static electricity?
     
  13. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    Absolutely certain. It also does this when struck with a piece of steel. As detailed above, ruby is known to sometimes exhibit this behavior and apparently this particular abrasive grain is manufactured in a way that permits it. It's triboluminescence. :)
     
  14. samuraistuart

    samuraistuart KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Dec 21, 2006

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