Post by rykk on Jul 3, 2014 16:16:11 GMT -5
Hi, y'all - I've been trying for a couple of weeks, now, to get a high polish on ALL areas of a large slab of Blue Pietersite, from the Namib, and just can't get a result that I'm happy enough with to send it to the slab's owner yet.
I'm using a 20" reciprocating vibratory lap. It's an old design Lortone I've modified for the reciprocal, rather than chaotic, action. It works - I've done lots of other rocks in it. My grit sequence is, 60/90 - 220 - 600 for 16 hours - 600 for 24 hours - then a Tin Oxide Polish phase. All of my grinds are longer than "spec" because the one Blue Pietersite slab is not mine. I'm polishing it for another member of this forum. I've achieved great results with just one 600 grit grind, but found that more obstinate rock species like quartz or agates need two grinds at 600 for a glassy shine, so I chose to play it safe and do two 600 grinds for this slab.
One of the four edges of this slab is very rough and there are definite, soft fibers sticking out of it. The slab has areas of flashy, light blue chatoyance and areas of darker, almost black, blue that are not flashy and appear to be softer - sorta brecciated, almost like a gabbro. My problem is that the darker areas don't polish as highly as the lighter, chatoyant areas and it's driving me nutz.
It appears, to me, like the darker areas are softer and might be where the flashy bits might need to be ground down to or are just more fibrous and softer than the "nicer" areas. I've run this slab for over a half a week on SnO and tried to even out the polish with a 12 Richardson's head, but nothing seems to work as good as I'd like. I've had the thought of maybe trying some Zam on a 4" buffer to brighten up the softer(?) areas. I've never polished this rock species before but I seem to recall a couple of slabs of the brighter colored Chinese Pietersite I did a few years ago may have had this problem, as well. All of the online pix of polished blue Pietersite I've seen have been of cabs or maybe a few slabs that had been wetted, so this phenomenon might not have been detectable.
Might it be that the cabbers just use the flashy parts of a slab and cut around most of the duller areas? Am I missing something fundamental in my process for this rock species? Or, am I just spending inordinate amounts of time trying to achieve something that's just not doable with this rock? I really want to do a super good job on this slab for this guy and have worked on it probably a lot longer than he expected and any help, advice, or knowledgeable experience would be very appreciated.
Thanks,
Rick
I'm using a 20" reciprocating vibratory lap. It's an old design Lortone I've modified for the reciprocal, rather than chaotic, action. It works - I've done lots of other rocks in it. My grit sequence is, 60/90 - 220 - 600 for 16 hours - 600 for 24 hours - then a Tin Oxide Polish phase. All of my grinds are longer than "spec" because the one Blue Pietersite slab is not mine. I'm polishing it for another member of this forum. I've achieved great results with just one 600 grit grind, but found that more obstinate rock species like quartz or agates need two grinds at 600 for a glassy shine, so I chose to play it safe and do two 600 grinds for this slab.
One of the four edges of this slab is very rough and there are definite, soft fibers sticking out of it. The slab has areas of flashy, light blue chatoyance and areas of darker, almost black, blue that are not flashy and appear to be softer - sorta brecciated, almost like a gabbro. My problem is that the darker areas don't polish as highly as the lighter, chatoyant areas and it's driving me nutz.
It appears, to me, like the darker areas are softer and might be where the flashy bits might need to be ground down to or are just more fibrous and softer than the "nicer" areas. I've run this slab for over a half a week on SnO and tried to even out the polish with a 12 Richardson's head, but nothing seems to work as good as I'd like. I've had the thought of maybe trying some Zam on a 4" buffer to brighten up the softer(?) areas. I've never polished this rock species before but I seem to recall a couple of slabs of the brighter colored Chinese Pietersite I did a few years ago may have had this problem, as well. All of the online pix of polished blue Pietersite I've seen have been of cabs or maybe a few slabs that had been wetted, so this phenomenon might not have been detectable.
Might it be that the cabbers just use the flashy parts of a slab and cut around most of the duller areas? Am I missing something fundamental in my process for this rock species? Or, am I just spending inordinate amounts of time trying to achieve something that's just not doable with this rock? I really want to do a super good job on this slab for this guy and have worked on it probably a lot longer than he expected and any help, advice, or knowledgeable experience would be very appreciated.
Thanks,
Rick