Another experimental cab - black spinel

As suggested to me in the garnet cab thread, a higher pre-polish allows tin oxide to put a mirror finish on the stuff. This bit also contained a surprise that's not visible in this photo - a star.



It's not strong and it only displays two rays when rotated in sunlight. Seems to have another two but very underdeveloped. Pretty sure I know the difference between black spinel and a sapphire so I checked up on it - yes, spinel can display asterism and the star is often four-pointed. I quite like the stuff, i think it should probably be used more often.

Very nice ,
This and the garnet ,they are both beauties
You seem to have got the round on these to so perfectly shaped.nice work

Lovely stuff Lefty Lee did one the other week got black muck everywhere

They scrub up good

Cheers

C&L

Cheers guys.

Yep, they do scrub up quite nicely. I have a tray of pieces but the biggest is probably about 15 carats. Don't seem to see them much bigger than that on the Anakie field, at least I haven't anyway. Yeah, getting little things that size to come to a perfectly round pre-form by eye is a bit tricky! :/ Took me a while. I wonder if there's a better way? They're too small to scribe a proper mark on but maybe the very small ovals and cicles that some of the templates have could be used as a guide of some sort?

I've got a piece of hornblende that would be about 25-30 carats if it were a sapphire, I reckon that would come up the same as the spinel.

Nice, I have two glasses full of blackjack, I will consider them now.

What equipment do you use to cab them?

GallicProspector said:

Nice, I have two glasses full of blackjack, I will consider them now.

What equipment do you use to cab them?

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I just shaped them on a #600 diamond lap on the little old Hall junior then went #800, #1200, #2000 and polished with tin oxide. Tin oxide took a while but worked well. I think a proper dished cabbing lap would have been better but it worked anyhow.

Here's an example of the camera refusing to see what the eye sees. This was a small Lowmead amethyst crystal with a spiderweb of inclusions through it, making it unsuitable for faceting. However, those same inclusions create an attractive colour play. I decided to see if I could cut it like a piece of opal, free shaping it to get the most out of the included area.

I think it came up very nicely and bears fair sort of resembalence to actual opal - there is a nice colour play throughout the stone, the full spectrum of colours in the mauve of the light-coloured amethyst. I reckon it's pretty effective. However, the camera does not see a highly-polished stone with a full play of colour through it, it sees it like this....



....a not-so-great polished stone with mostly white light being reflected back. It just doesn't seem to be able to see the spectrum of colours being refracted back. I promise, it looks nothing like this to the eye.

Richard, check your Lowmead crystals closely to see if any display an opalecent look inside - it's worth having a go at

Quite a few of mine have that rainbow display,will definitely try cabbing a few and see if I can get that play of colour like yours has.

How hard was this to cab? I'm still practicing with agate mostly.

Was pretty easy Richard - just sort of have to look over the thing closely to get the flash facing the the right direction to get the most and best out of it.

BTW, will be at the Bundy gem show about 10am Saturday I reckon.

I should be there around the same time,will have to catch up and compare notes

Those are great stones Lefty! I can imagine what the amethyst looks like, having seen something like it before, but can't do the same for the star spinel.
A trick is to take more than one pic: one in indoor lighting, one in overcast or shade outside daylight and one in full sun (at an angle, morning sun is good). Also set your camera to macro and get the object as close to the lens as possible. After all that, use a web app like pixlr (here: http://apps.pixlr.com/editor/ or you can add it to your browser as an extension) to crop the image to take out all the noise and you'll get something like this:


If it turns out that none of your pictures give a good representation of the stone, shoot a sort video outside in daylight where you move it around to show several angles.

Very nice heart there Piep! Is that agate?

I think the problem with trying to take the photo might be that the object has a highly reflective surface but is transparent with several layers of highly reflective surfaces inside and the camera struggles to know what to focus on.

Plus the camera only has one eye Lefty, we have two, that's why opals look like crap on photo actually.No wonder this stone must be incredible with two eyes Something that can be useful is having a completely manual mode on your camera, because to shoot stuff like this, it's better to be able to close the aperture A LOT to get the depth of field to be wide enough. DSLRs are the best option of course, but you'll have to sell some stones first, and to sell them, you need good pictures, rinse, repeat