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Llyn Idwal Bubbles

Here's a little reference post about bubbles for anyone interested...

It was, I think, @Bowmaker who first mentioned to me about a 'bubbly' appearance as distinguishing feature on the surface of the Idwal stone. Now I've had a couple of them before and neither as shown this, but then there were a few quarries around Llyn Idwal I believe, and the stones do vary in appearance and use. So it wasn't until recently that I'd really seen the Idwal bubbles first hand.

Here's a mystery stone I got off ebay:

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Bubbly innit! And you can see too the kinda flakey-flinty fissures that are also typical of Idwals.

But the surface was so irregular that I wasn't sure, and when I tried it I wasn't convinced either; it was fast as hell, and maybe topped out around 4k, if that. An *excellent* stone, but not as fine as an Idwal.

That surface above was quite badly dished so I decided to lap it flat this evening. Here after a couple of mins:

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In that picture the bit on the right has been lapped, which has removed the bubbles to reveal the surface below. It's very clearly an Idwal now - those black lines and speckles are dead giveaways.

So what's going on with on with the bubbles...? Here's another closeup with some of that flinty, cherty character too:

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The bubbles on a Llyn Idwal are a surface feature, and effectively minute, circular, cracking. You can lap through them - they don't go through the stone.

This is now flat, some of the larger bubbles are still visible, but I can't be arsed to go any further:

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And here dry, after being used with oil. You can see that the bubbles are mostly in the middle, which I've lapped less because it was dished to begin with:

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The stone is now *much* finer and slower than it was before; you could finish a razor on this now, it's very similar to a Charnley. Initially I was basically sharpening on a surface that was quite rough due to having very fine cracks all over it. They didn't come away at all - it wasn't flakey - but that's what was happening.

I have no idea what causes this, but I suspect over time it would probably come back if not kept oiled. I imagine something to do with the surface drying out to reveal an aspect of the stone's structure not normally visible or noticeable in use (?)

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Interesting eh! Anyone else noticed this before / got any thoughts? I'm sure I can't be the first person to comment on it...
 
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