Once you understand what jade is doing, it is the easiest things in
the world to get a great polish on.
Jadeite is easy to polish, so I am going to talk about nephrite.
Most of my cutting is done with Wyoming jade.
nephrite is a dense structure of interlocking fibers, although I
have never actually measured this with a scanning electron
microscope, which would be proper, here is what I have observed:
when cutting with a saw, or grinding, these fibers to pull apart from
each other. although they stay in place, the “pulling apart” causes
loss of optical transmission continuity, aka subsurface damage, also
known as subsurface fractures.
in a faceted stone, this damage would be obvious and visible, as
cracks and flaws. in a piece of jade, the fractures are not so
obvious, but they are still there, and will make themselves known as
the stone will appear to not take a proper polish.
sanding, as opposed to grinding, removes the damaged portion of the
here is the important part: you can calculate the amount of
subsurface damage you are going to get. Again, I have not measured
this with an SEM, but the amount of damage appears to be about 1.5
times the grain size of the abrasive used to grind. So, if you grind
with an 80 grit wheel, which uses an abrasive of about 1/80 of an
inch or 0.0125", you are going to have damage of about 0.016- 0.019".
roughly equivalent to the thickness of a, what, 26 gauge piece of
when you grind on a 120 grit wheel, these numbers change
so, using the 80 grit example, during sanding you will need to
remove the 0.016" damaged surface, to get down to the undamaged
subsurface material that has optical continuity.
note: when you take a slab of jade off of your slab saw, the ENTIRE
surface of the slab has subsurface damage - so when you wet it to
see the color, all you are going to see is a dull, frosted subdued
color. you have to polish a test area to see what the jade is
actually going to look like. I have cut 100’s of pieces of jade -
every time that I am absolutely sure that I have a dud, I polish it -
2/3 of the time it really is yard rock, the rest of the time it is
some of the best material i have. So much for experience.
so, that is the theory, hope it helps
to see some examples of polished jade, please denvergemshow.com
Mark Zirinsky, Denver