WEIRD: "Bull Thistle" Sharpening Stone Sparks

FortyTwoBlades

FortyTwoBlades

Baryonyx walkeri
Dealer / Materials Provider
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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]
 
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:
 
They're freakin magic!

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

Benchstone please!
 
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
 
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..
 
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.
 
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.
 
Rey HRH said:
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.
Click to expand...

As noted in the post above, I've narrowed the phenomenon down to triboluminescence of the ruby grit. No magnesium or titanium involved. :)
 
Rey HRH said:
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.
Click to expand...

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
 
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.
 
DavidHoback said:
Are you sure it's not just static electricity?
Click to expand...

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. :)
 
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