Boulder Matrix opal cutting: how should I approach that rough?

[Sodabowski]

G'day all,

So I've got these three big pieces of boulder from the Comet, cut my teeth on the freebie the seller had sent along, which was easy: a single flat veil inside the matrix of ironstone. But then, for the big pieces I don't want to risk ruining them. They're kinda onion-shaped, in that the opal layers are at the core, with matrix all around. So, how do the seasoned cutters among you approach that material to make the most of it?

The last one I polished (underwater not to risk any heat on it) to get a better insight.

Any experienced advice on what direction to slice it up, pretty please?

 

[Jaydo]

Sorry cant offer any help but watching with interest

Boulder Opal looks amazing when cut, that is my next goal

 

[Danielkrupski]

There really isn't much opal to work with. I would go with the first pic try to highlight the white layer then you get the browns white and bluish green opal. I'm no expert just an opinion. Maybe wait till one of the cutters from the ridge put a reply.

 

[Sodabowski]

Yup, definitely need a pro advice to avoid ruining that material, there's more than meets the eye in that stuff.

 

[Jukebox]

With boulder you gotta watch out to how sandy the material is, as it will just waste away on the wheel infront of your eyes.
The most interesting piece you got there is the swirly one which appears to be the most sandy around the bloody opal you want to get at.
From personal experience that opal will disintegrate as soon as you put slightly high pressured water near it - so you wont be able to get a polish on it.
If your game you could try it but i have worked that type of stuff before and it doesnt turn out well.

The other two you got there i would saw into two or so pieces - try a seam to open up one side. I prefer this method because if you grind away the whole you can wind up wishing you hadnt as now you dont have a backing.

Just remember that the white clear opal cracks like a mofo as well so i always try to avoid it at all costs when putting it on the sw.

 

[Karen]

With the first piece Jukebox is right, the lighter sandy bits will disintegrate very fast if put to the grinder.
If you were ok with an uneven finished surface on the white opal section Id carefully hand sand individual sections of it with a fine grain of sandpaper or Dremell (details below). Then as you get closer to the white opal surface change to a "very" fine sandpaper. Just keep in mind that you will probably end up with an uneven surface, not a flat shiny one.
I wouldn't then sand the white opal down to make a flat surface. You would lose too much opal.
The second pic shows on the side how deep some of the sand goes so you can see the surface shape youd be left with if you removed those small sandy bits.
You could cut around the white opal but then what would you make out of that small piece? Before you make the decision, try and have a look into the white opal to see if it looks cracked or flakey. It looks pretty solid from the pics youve posted but pics can't replace looking at the real thing.
Depends how brave you are or if youre happy with a paper weight.
I worked as an opal cutter in Sydney many years ago and with pieces like the ones you have we sculpted the surrounding ironstone into decorative shapes and sanded back any small bits of sand on the opal to make a unique piece. One of my pieces ended up looking like one side of the opera house with the front section covered in opal.

The second stone I wouldnt cut at all. The colour seams look too thin. You could try sanding out the sandy bits. But it looks very crumbly.
I've cut stones similar to this and as Jukebox says, they just disappear before your eyes.

A Dremell is a small drill with tiny attachments. Small enough head to gently sand away the top bits to reveal any opal underneath.
I was always going to try sculpting and sanding boulder opal with one of these but never got the chance, so not sure how effective they would be.

Hope that helps some. Good luck!

 

[Sodabowski]

Thanks for the feedback guys. I haven't touched these yet. Karen I have had a Dremel for like 20 years, I exclusively cut and polish stones with it (until I get the means to buy or build a proper cabbing machine). I'll try the second one since it really is sandy and looks like a lost battle in advance, so not much to lose anyway.