Topaz scratches (aka should've known better)

[RoughCreations]

This thread is designed to hopefully prevent others making the same stupid mistakes as me.

I decided to cut the great AB Facet Design's Diamond Bar 4:1 from Volume 5. My previously cut Diamond Bar 3:1 came out so well in quartz I thought I would try the longer option in topaz (https://aussielapidaryforum.com/forum/index.php?topic=6980.msg62816#msg62816). I have had two big chunks of O'Briens topaz sitting around for a few years, the first one of the matching pair cut real nice previously, so I was not expecting problems. I used my trim saw to cut a couple of slits to get a rectangular prism shape, and dopped it. See video below. The thing about the Diamond Bar designs are that the crown has lots of low angle facets, less than 10 degrees off the central table facet (the 3:1 version has no table). The angles increase as you move to the edges of the design.


Can you see my obvious mistake? Big Hint: that flat window I roughly polished in the side to check for inclusions was already a bit shiny...

The problem: scratches no matter what I tried.

If I had been concentrating and not so complacent when I dopped it I would have rotated the rough prism by 90 degrees along the long-axis before dopping. This would have meant that the low angle crown facets would have been at ~90 degrees to the cleavage. I still would have had the two large vertical G1 facets parallel to cleavage though, so a much better solution would have been to rotate the cut slits by 25 degrees roughly, so that none of the facets are less than 10 degrees to cleavage, including the simple pavilion.

Love this faceting craft - just when you start feeling like an experienced facetor, it regularly brings you down and makes you feel like a newby once again. You just start getting over-confident thinking you have mastered some aspect, when it brings you crashing back down to earth and having to go back to the basics.

Before I realised the cause of my polishing woes, here are some of the things I tried, including ideas gleaned from an old thread (https://aussielapidaryforum.com/forum/index.php?topic=4821.0) on ALF nonetheless:

• 60k diamond on Battlap, sand Battlap with 600 wet and dry first. Rub disk with stone manually: scratched
• Cerium oxide on a perspex/polycarbonate disk: no effect
• Aluminium oxide on a perspex/polycarbonate disk: scratching
• Zirconium oxide on a perspex/polycarbonate disk: no effect
• Cerium oxide on a pewter disk: no effect
• Aluminium oxide on a pewter disk: scratched more
• Aluminium oxide on a thick Darkside: small scratches
• Cerium oxide on a thick Darkside: scratched more
• 60K diamond on a Darkside: scratched
• pre-polish 14K on copper, then Aluminium oxide on a pewter disk: big scratches
• My new resin-bonded 60K diamond disk: also scratched. Worked well on facets not on cleavage though.

On close examination under high magnification after several weeks of pain, I noticed that little wedges of topaz were being detached on the polishing plane, then the pieces were tumbling around and scratching any polish that had already been managed. This even happened when using a stationary lap, and manual polish, which is a first!

On reflection, I have successfully cut plenty of topaz without giving the cleavage much thought. What brought me undone this time was the large number of large facets close to the cleavage plane. Other designs in the past were lucky to have one or two small facets close to the cleavage, which were manageable and not given much thought. It's also possible that this chunk of topaz has extra well-developed cleavage for some reason, adding to the problems. It does have some rutile inclusions here and there also.

RC

[MakkyBrown]

What diameter is your dop, I'll have a go if you want.

[yakapari]

Hi, I`ve recently started faceting some Obriens Creek topaz that I bought from one of the guys that live on the field. It became to hot late July/August to dig past 10am so, bugger it, out the wallet came 

O'briens creek topaz seems like a much harder stone than the New England topaz I have cut before.

I use Alumininium Oxide on a Batt lap for final polish for what I think is a satisfactory end result, though I am finding some stones need more time on the polishing lap than others.

I have read somewhere a good oxide polish is equal to about a 60K diamond polish, so I will continue using AO on these stones.

[RoughCreations]

What diameter is your dop, I'll have a go if you want.

You're on!
6.25mm

[Faceting Frank]

1/4 inch is 6.35mm. Not that the 0.1mm might make a difference in most quills.

[MakkyBrown]

If it will grip it should do, will be close. More concern about how curved my laps are, might have to put them ob the lathe, if the facets are huge.

[Bucket]

Bloody hell RC, that's a gnarly looking piece of topaz! Most of the pieces I have from O'Briens Creek are water worn jellybeans that can be a bit hard to pick the cleavage plain. I did facet a nice blue one, that polished beautifully (not rubbing it in at all) on 50k diamond on pewter, but unfortunately when I tried to fit it into a ring setting I made, when rolling one of the claws over, it broke along the cleavage, lost about 25% of the stone! I still haven't recut it.

[RoughCreations]

If it will grip it should do, will be close. More concern about how curved my laps are, might have to put them ob the lathe, if the facets are huge.

Ok, I took my topaz to MakkyBrown to see what he could do. After a bit of mucking around getting the alignment correct, MB managed to get a polish! 1200 diamond on pewter, followed by 100,000 on another pewter disk, Both disks were knurled (my pewter disk isn't).
So it's officially me... 
Maybe I should have stayed with my quartzes.
He kindly gave me some of his 100K diamond mix to try, I only have some pre-mixed paste that I'm not sure about. MB also lent me his knurler, so I will see if that is important, too.

RC

[RoughCreations]

Bloody hell RC, that's a gnarly looking piece of topaz! Most of the pieces I have from O'Briens Creek are water worn jellybeans that can be a bit hard to pick the cleavage plain. I did facet a nice blue one, that polished beautifully (not rubbing it in at all) on 50k diamond on pewter, but unfortunately when I tried to fit it into a ring setting I made, when rolling one of the claws over, it broke along the cleavage, lost about 25% of the stone! I still haven't recut it.

Yeah, I got a couple of chunks from someone on Fleabay, think they had had them for many years. Below is an old photo I took of the originals.
Maybe enough time has passed now to re-acquaint yourself with your topaz.

[RoughCreations]

Hi, I`ve recently started faceting some Obriens Creek topaz that I bought from one of the guys that live on the field. It became to hot late July/August to dig past 10am so, bugger it, out the wallet came 

O'briens creek topaz seems like a much harder stone than the New England topaz I have cut before.

I use Alumininium Oxide on a Batt lap for final polish for what I think is a satisfactory end result, though I am finding some stones need more time on the polishing lap than others.

I have read somewhere a good oxide polish is equal to about a 60K diamond polish, so I will continue using AO on these stones.

I don't think I have managed to get oxide to work with topaz. It's a pity, as I like working with oxides generally. Nice haul there by the way, and good book too, lol.

RC