Skin polishing Sapphires in tumbler

[hithwentinuviel]

Hi. I have a bulk amount of rough sapphires that are about 2mm-7mm in size. I am wanting to just skin polish them so when kids are fossicking for them at my gem show, they sparkle. What would be needed grit wise in a tumbler to just skin polish and not eat away too much of the stone. Or would just running them in the tumbler with a bit of water help polish them.

[Aussie Sapphire]

Hi. I have a bulk amount of rough sapphires that are about 2mm-7mm in size. I am wanting to just skin polish them so when kids are fossicking for them at my gem show, they sparkle. What would be needed grit wise in a tumbler to just skin polish and not eat away too much of the stone.

You will need diamond grit - this is expensive and will take a long time.

[Aussie Sapphire]

Or would just running them in the tumbler with a bit of water help polish them.

NO - it wont really do anything. 

We get asked about this a lot and I usually try and talk people out of it.  We can supply tumbling grade diamond in a very small bowl (preferably vibe tumbler) but it not an easy thing - we dont really recommend trying.

cheers
Leah

[Johba]

Gidday there, we also have some low grade sapphires we sourced from a commercial mine in Rubyvale QLD where we given instructions on how to tumble these. You will need #600 diamond grit 10ct @$10 and tumble for 2-3 weeks then a final polish with #100,000 diamond grit 10 ct at the same price, can buy from Skippy Gems in Sapphire QLD or their online store. We have these underway and will let you know how they go.

[Bucket]

Hi Johba, welcome to the forum. I haven't had any experience with tumbling sapphire, but I know that 10 ct of diamond grit won't go far in a tumbler, unless your tumbler is very small and you're only doing a few sapphires. Also, the end product might not be as great as you'd hoped working on only two grits, particularly if you've got some rough edges to start with. Just a heads up, with normal tumbling, we work through 4 or 5 grits depending on the material we're working with, usually about a week on each. For around 1 kg of stone we'll use around 50 -100 grams of grit depending on the hardness of the material. Working on even a similar ration, 10 cts of diamond will only cover 100 cts of sapphire. I wouldn't like you to be disappointed.

[Johba]

Thank you Bucket for your valuable feedback, we source are sapphires and gemstones from Armfest Pty Ltd in Sapphire QLD, they are a commercial mine where we purchase the graded wash to fossick. The stones we find are then graded onsite where we have a mixture of sapphire, spinel, zircon and topaz. They range in size from 2mm up to 8mm the total mass would not exceed 100 cts. We have a few tagged as tumbling and Armfest
supplied us with a Tumbling guide of which listed the type of Hobby tumbler (National Geographic) and then the tumbler durations and the grinding mediums required to polish these. So we will have to see how we go.

[Bucket]

Armfest are who I generally go to when I'm up there and want to fill in some time. I generally don't have time to go onto the field and dig, although I did once out at The Willows on a 35+ degree day, bloody hard work I can tell you! On one of our mornings at Armfest we walked away with what turned out to be 27 cutters, too small for me but sent them to Thailand and were very pleased with what we (eventually) got back. Very civilized with drinks available and benches to turn your sieves onto, saves the back!

[Johba]

Hey Bucket we have a series of diamond grit through the tumbler with what sapphire’s we have for 6 weeks in total time through the following grits. #600 for 3 weeks, then 2 weeks on #100,000. The sapphires have come out nice and rounded but have dulled. Should I run these through some intermediate grit? I have another lot tumbling now and have been through 2 weeks on the #3000 grit then we will try #8000 grit for 2/3 weeks then the final 2/3 weeks on the 100,000 grit.

[Bucket]

I'm really not sure, 100,000 grit should be fine enough to polish sapphire so the only thing I can think of is that maybe you need something between. It's a fairly big jump from 600 to 100K I'd look closely at your results from the current lot you have on and see if that makes a difference. I know with faceting that jumping that much between grits wouldn't give me the desired results.  How long do you have left on the ones you have in? I assume that the stones are waterworn when you start, if they are I would look closely at 600, 1200, 3000, and then 100k. You should inspect the stones and wash them thoroughly between grits, any transference will contaminate the next step and your results will be poor. The stones after the 3000 (maybe even the 1200) should display at least a dull shine.  As I said, I've not tumbled sapphire before myself, I'm basing these comments on my experience with general tumbling. I know with agate (hardness around 7 ish) after 1200 it shows a semi shine. Sapphire is a lot harder (9) and should also be displaying a semi or dull shine around that girt.

[Johba]

Thanks Mate, I am currently on the second week of the #8000 grit the sapphires and spinel are well rounded with a dull shine will take your advise and run through the spectrum of grits that I have, it does look like that I need to run 3 weeks per grit then 24hr rinse between.
What diamond grit I have - #600, #3000, #8000 and #100,000

[Bucket]

Just out of curiosity, did you loose much size on the first lot you did? At the club with assorted gemstones, we usually do around a week per grit, with good results, but some stones (obviously the softer ones) end up quite a bit smaller. With the hardness of the sapphire, I'm wondering how much size you lost during the extra time you had them on.

[Johba]

Bucket, we
Lost a little from the sapphires these were mixed also with Spinel, zircons. The sapphires we have were green, light green blue, light blue with clear and red
Zircons. The Zircons have worn most of all. I contacted Carol from Armfest to ask as she put me onto the tumbling process, she advised that they need at
Least 3 weeks for each grit size.

[Bucket]

It figures with the zircons, they would probably be the softest of the three you mentioned. Sounds like Armfest have you covered, good luck with the current lot!