Jade

[Cougar Allen]

(I wrote this to answer Tom Carey's question in the Ivory thread, but then I decided it ought to be in a thread of its own. I hope I covered everything....)

I cut jade back when I did lapidary work as a hobby. It's the toughest of all natural stones so it's a natural choice for a knife handle (agate is also good). Jade comes in all colors and in different patterns. It's available in slabs, usually 1/4 to 3/8" thick (6.5-9.5mm) but you can have it slabbed to any thickness you want. Unlike most gemstones it's available in large pieces; it's found in the form of boulders.

There are two similar minerals that are called jade; nephrite and jadite -- both are about equally suitable for a knife handle though nephrite has a fibrous grain and it's often a little tougher.

Jade (both kinds) is notoriously difficult to polish -- orange-peel. It varies; sometimes it polishes up easily and other times it'll drive you nuts with orange-peel. I've had good results with Raybrite A on leather, not too wet. Prepolish is important; you can hardly spend too much time on prepolish. If you're getting orange-peel try letting the lap dry out a little or wetting it a little more, try a different speed, either slower or faster ... you have to experiment.

Pick up a Lapidary Journal for sources. You can get Raybrite A there too. I don't think you'll have any luck polishing jade with the compounds a knifemaker is likely to have on hand. I've had much better results with Raybrite A than with cerium oxide.

If you're already set up for grinding and polishing knives all you'll need is a diamond trim saw and a jar of Raybrite A; you already have everything else you need. You could get it pre-cut to the dimensions you want for a small extra charge and save buying a diamond saw of your own if you're not planning to make a lot of stone handles.

Jade varies greatly in color and translucency and uniformity and the price varies a lot accordingly.

-Cougar Allen :{)

 

[george tichbourne]

I have had a slab of jade in the drawer for the past several years that had been waterjet cut and displays some splitting at the edges because of water pressure and I have been reluctant to begin work on it in fear that the splitting along grain lines.

Is there a resin that would stabilize the cut edges, and how would it be injected into the cracks?



------------------
george
www.tichbourneknives.com
sales@tichbourneknives.com

 

[Snickersnee]

The Maori of New Zealand use "greenstone" in their war clubs, that are about the size and shape of a meat cleaver.

Is greenstone related to jade?

 

[Tom Carey]

Cougar,

Thanks for the great info. I will be offering the Jade in custom sizes as well as slabs and rocks since folks are asking for all three. How do you tell which type of Jade you have? Can you find both types in the same area?

Regards,

Tom Carey

 

[Cougar Allen]

That "greenstone" is probably jade, though it might be some other tough stone. One of the most important technological advances of the neolithic revolution was the technique of grinding and polishing stone, allowing jade to be made into much tougher tools than flint or anything brittle enough to be knapped....

You can fill cracks in stone with a cyanoacrilic similar to superglue, but a knife handle has to be very strong ... can you grind off the cracked part and get to solid stone? It might pay to fill the cracks before grinding just so they don't spread. You can get stuff made for the purpose from lapidary suppliers (pick up a Lapidary Journal and send for some catalogs) but superglue would probably be good enough if you're going to grind down to solid stone, and I think you should.

Nephrite often has a fibrous grain visible to the naked eye and it's usually visible under 20x magnification. Telling the difference between nephrite and jadite requires experience and it sometimes requires a specific gravity test to be really sure. People who are familiar with jade will just glance at a piece and tell you which it is based on the luster, but we're occasionally wrong.

Cutting gemstones involves going through many stages of progressively finer grits. I used a typical silicon carbide setup, grinding and sanding wet with a drip feed. I did my coarse grinding on a 100 grit wheel, then used a 220 grit wheel, then went to rubber-backed silicon carbide wet paper starting with 220 grit (effectively finer than the 220 grit wheel because of the rubber backing and because paper is only the nominal grit size when you begin to use it; 220 grit paper turns into 600 grit in no time). Then I went through 400 grit, 600 grit, and I used an old 600 grit disk for prepolish -- it was actually maybe 3000 grit or finer -- then polishing with Raybrite A on rock felt for most stones, on leather for stones that tend to orange-peel like jade and malachite.

So that's a 7-stage process from grinding to polishing -- that's pretty typical. It may sound like a lot of steps, but if you use fewer stages then each stage takes longer. Gemstones are hard and removing the scratches from the last stage takes longer than you might expect even when you're sanding off 220 grit scratches with 400 grit.... If you use diamond you'd use finer grits across the board. You don't need the water spray or drip feed ... it's definitely better to use it but you can do it dry on your knife-grinding equipment; you'll just have to go slower.

I've read articles written by people who wanted to get into gem cutting and had a belt grinder already so they used that. It's not ideal but it works. Just use progressively finer grits and slow down your machine so you don't overheat the stone and crack it. If you're used to grinding blades so fast and with so much pressure you have to wear heavy leather gloves because the blade gets too hot to hold ... that's not going to work with stone.

It's customary to use "dopping wax" to stick a stone to a dowel (dop stick) to use for a handle. You can get dopping wax from those catalogs you sent away for. You can also use epoxy or superglue instead, but dopping wax is convenient and it'll keep you from getting the stone too hot (the wax would melt and the stone would fall off).

There's a lot to cutting gemstones; it's a whole hobby or business in itself (and cutting faceted stones is a different game entirely; you need special equipment for that) but if you've been making knives for a while you shouldn't have too much trouble making jade or agate scales -- it's basically the same kind of thing you're doing already, just with a harder material.

-Cougar Allen :{)

 

[Tom Carey]

Cougar,

Thanks for all of the additional info. I am acutally looking at getting into gems as well at this point. Are there any books or Lapidery suppliers that you would reccomend checking out? I like to know as much as I can about the items I am selling.


Regards,

Tom Carey

 

[Cougar Allen]

It's been a while so I don't have up-to-date info.... Lapidary Journal is the essential source. I used to buy things from the Greiger's catalog but then I found a local rock shop where I could get better deals and good advice too. Books ... I'll have to look through my collection and get back to you ... I have too many books and I don't know where the lapidary books are ... I had my library organized once but that was a long time ago.
Definitely get a subscription to Lapidary Journal; that's essential, and see if you have any rock shops in driving distance. I'll try to get back to you with more info.

I think this thread should probably continue here rather than move to email -- I bet there are others here who are interested, maybe even in setting faceted stones in pommels -- I have a friend who does faceting and he could cut anything you want to order. Actually it's not hard to find someone to cut stones to order, but he does good work for reasonable prices and besides he's a friend....

-Cougar Allen :{)