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Polishing Jet - it's just not shiny


#1

Hi, I grind and polish a variety of stones. I have two types of Jet, one is somewhat soft, the other is very hard. It’s the hard one I’m having problems with. The softer Jet polishes to a mirror finish. The Hard is very matte like, it’s very hard to “see” the Jet.
Grind with diamond: 100 (shaping), 500 (more shaping a polish front and back, 800 (pre-polish), 1200 (polish). I do have a 3,000 K lap.
Sandpaper: 1000, 1500.
Luxi Polish: Blue then White
Diamond Polish on Felt pad: 14,000 then 50,000 k.
(I have Googled, searched archives and forums, no luck)
Pic: One on the left is soft, hard is on the right.
(Been a member of Ganoksin since 1994, best on the net for info on stones and jewelry)
Hope you can give me some advice.
Tony


Looking for Amber & Jet Cabs
#2

It’s been years since I’ve done any lapidary work, but back in the 90’s I cut a LOT of petosky stones and various other soft stones (corals, shell, even lapis) for a business in my home town. We used Dico Blue Buffing compound on the soft stones and it polished them beautifully. If I recall correctly, you could go right from about 600 grit to the buffing compound and come out with a highly-polished finish. I’m guessing that jet would behave the same way though I’ve never worked with it and can’t know for sure.


#3

I do all of my lapidary work on plated diamond grinding wheels and diamond resin wheels. They work well for just about any material and are very nice for hard agates. Big improvement over crystal pads with diamond or the silicon carbide belts that I started on. I still sometimes use plated laps and various oxides on felt or crystal pads for final polish. The harder stone looks like it is undercutting or orange peel. Research how you deal with this type of problem. The best resource for me is to study the Kingsley North catalog. I sometimes also go to whatever OEM they sell for whose catalog description might help solve your problem or be of interest to you. Kingsley North is also great to work with…Rob


#4

My experience is that jet will often remain a bit dull or matt after polishing. I can’t explain why that is, just know it is. I usually use it as a more durable alternative to a black onyx inlay and try to remember to warn people that it may not be high polished when finished.
Mark


#5

That’s interesting! I had a project about 2 years ago that I was going to use jet for, but was worried about its durability. I ended up not doing it, but I had no idea it could be more durable than black onyx. I thought it would’ve been softer and consequently more brittle. Could you explain a bit more about it being more durable please? Thanks!


#6

Try cerium oxide on leather.


#7

I have a stone cutter that I use and the jet has been his recommendation. It’s less brittle than onyx. He’s not the only cutter that’s told me that. In the late 80’s, early 90’s I made a ton of multi stone inlay pieces. It was the thing. I trusted the cutter. Sorry I can’t give you more detail.


#8

Ah, brittleness! That makes sense. Thanks for the reply. I think perhaps I’ll try that project after all one of these days.

Thanks again!
Erich


#9

Thank you all for your suggestions.
I’m still working on this and will let you know what works!
Thanks, Tony


#10

Hi Cam, Have you tried Zam. Works great with softer stones. Vince
LaRochelle


#11

Try wetting your 50k diamond disc with vinegar instead of water. If no luck, try Linde A polish next. Try slower speeds (use middle of disc). If still no luck, borrow a little Holy Cow polish from a friend who may still have some. Optical grade cerium oxide might work - some folks say that was the secret formula for Holy Cow. Still others swap ear by a silicon carbide belt…

Lorraine


#12

I’d love to hear more on this subject. I bought a small piece of jet from near its renaissance (ie where it fell out of the cliff) at Whitby in North Yorkshire UK. I’ve made one wide-bezel ring having been informed by a Whitby jet worker that this is the way jet is set - in a wide bezel glued in with epoxy adhesive mixed with coal dust.

Any alternative views?

Gingernuts. In South Devon.


#13

Jet is a form of, or at least closely related to, lignite and hence similar
in origin to amber. Since hand-rubbing with toothpaste (Colgate) on a soft
cloth is a classic polish for amber I would try something like that.

Cheers
Hans Durstling
contract lapidary
Moncton, Canada


#14

Hi again, Tony,

In addition to the polishes I mentioned in my earlier reply, it also occurs to me that moving from 100 grit right to 500 might be too steep. My usual grit sequence -hardly original; used by many others- is: 80, 220, 280, 600, 1200, 3000, then whatever hi-grit diamond polish works, usually 15,000 and up.

Also check your water flow over whatever grinding surface you’re using. If you’re using a Diamond Pacific Genie, with just that little bottom spritzer thing to recycle the same water onto the bottoms (!) of the wheels, in my experience residue can build up on the wheel and cause scratches and tear-out: the 2 sets of 3 wheels are sharing water, so your nice 500-grit wheel can pick up larger pieces of debris from the 100-grit wheel. And the whole wheel does not get rinsed. Whereas a design similar to a CabKing with its copious overhead water flow – or any grinder with an add-on fresh water supply like Hi-Tech’s All-U-Need, to flood the wheel – should rinse away contaminants AND keep the wheel cooler.

If you’re using a flat lap, are your laps really, really clean?

And finally, it could be the material itself. Jet only has a Mohs hardness of 2.5 to 4 – that’s not very hard!

Some stones have natural pits. Or possibly whoever slabbed it should have cut the rough 90 degrees around from your surface plane. If this is the case, you should be able to get a good polish on an edge: with 100 grit, regrind one edge to a steep edge and step through the rest of the grits to see how well the edge polishes.

If the stone turns out to have natural pits, you could try stabilizing it with Opticon and redo the polishing. (Of course if you then sell the stone, the right approach is to disclose to the client that it has been stabilized.)

It’s hard to tell from photos whether that’s the dreaded orange-peel effect. If it is, it usually happens later, in polishing, not in grinding. But if those are scratches or pits, you should be able to see them with the naked eye. Do you have a 10x loupe to examine the surface? There are books full of theories about polishing: eg, slow speeds vs faster speeds, so experimenting might be your best bet.

http://orchid.ganoksin.com/users/cam cam
February 26

Hi, I grind and polish a variety of stones. I have two types of Jet, one is somewhat soft, the other is very hard. It’s the hard one I’m having problems with. The softer Jet polishes to a mirror finish. The Hard is very matte like, it’s very hard to “see” the Jet.
Grind with diamond: 100 (shaping), 500 (more shaping a polish front and back, 800 (pre-polish), 1200 (polish). I do have a 3,000 K lap.
Sandpaper: 1000, 1500.
Luxi Polish: Blue then White
Diamond Polish on Felt pad: 14,000 then 50,000 k.
(I have Googled, searched archives and forums, no luck)
Pic: One on the left is soft, hard is on the right.
(Been a member of Ganoksin since 1994, best on the net for info on stones and jewelry)
Hope you can give me some advice.
Tony

http://orchid.ganoksin.com/uploads/db0786/original/2X/3/3cf81ffe5fb373b16f5bbb52986ade9dd5093b33.jpeg


#15

Make sure the Jet is completely dry. It’s best to leave sit over night…

Then I use Zam and a flannel buff on a standard 3450 RPM buffer. I use a separate stick of Zam and a separate buff because Jet is so messy.

Rick Copeland
Rocky Mountain Wonders.


#16

I found Luxi White gave a high finish.


#17

Hi Dear,

Any idea about PIC 100 G2 by Envision , how much and from where I may get it in USA .

Thanks for help.

Emad Ghali


#18

Hi and Thank You all very much.
Betty2: Used Cerium Oxide, not much change. Vincent, rockdewd: Used Zam, same. jagwallen: I use Luxi blue then white, still not that mirror shine.
SO, went over to my “rock dealer” who sold me the Jet, he said that some of the pieces just will not go mirror shine. So it’s actually and most likely the stone itself.
LORRAINE, wow, thank you very much for your suggestions. Yep, need a 220 and a 280 grit. Am also doing the vinegar treatment on the 50K you suggested. My laps are flat laps and I don’t have a recirculating system, only clean water. I cut a piece of red jasper yesterday then put it through the pre-polish and polish up to 3000k lap. Used 9.5K then 14K then 50K then 100K diamond paste. Shines like crazy, so I’m thinking it’s probably not the lap. Did look at the Jet with a 10x and 20x loupe and not much to see in the way of scratches.
Since my other piece of Jet polished up quite nicely I’ll do my best to get some more of that.
jagwallen: you’re that close to Whitby! WOW. I’ve seen pics of that Jet, it’s really fantastic. Good on you!
Again, to all who replied in this thread, thanks. It’s a really great forum, Thanks Ganoksin!
Tony


#19

If it was my work I would go back to the 500-800 grit and redo all after. the pic looks like some scratches were left behind.


#20

To further explain my experience with Whitby jet:

On visiting Whitby I spoke to folk working in a couple of the jet craft shops. I was told that due to its soft nature jet isn’t typically formed into cabochons and then set in rubover settings. Instead it is glued into a wide bezel using epoxy adhesive, often mixed with coal dust. The set stone, and its bezel, is then shaped with files, wet and dry paper of various grades and finally with appropriate grades of polish on a conventional mop and bench motor combination.

I followed those instructions and achieved a very acceptable shine. The method does limit the use of the stone to some extent but fits quite well with my ‘craft’ approach.

Jet cut with a piercing saw, shaped, fitted and then glued into a wide walled bezel.

Stone filed, sanded and polished with white Luxi.

I hope this helps.

Regards.

John in Dartmouth South Devon, about 380 miles/7 hours drive from Whitby.