Aussie Lapidary Forum
LAPIDARY => Tumblers and Media => Topic started by: crocdoc on March 28, 2010, 07:46:18 PM
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This is my first post and, as the title suggests, I am an absolute newbie at rock polishing. I picked up a tumbler for my young god-daughter for Xmas (Lortone double barrel) and collected a pile of interesting looking rocks for her while on a recent road trip around Cape York. Mostly quartz, granite and a few other odds and ends.
We put the rocks through 5-7 days each of #80, #220 and #600 silicon carbide, cleaning thoroughly between steps, and were impressed at how quickly they were taking shape and becoming smooth. Very excited about seeing the final product, we put the rocks through their final stage of cerium oxide, but when we opened the barrels after 5 days to our disappointment the rocks were almost all pitted and/or broken. I can understand that there would be scratches on the smooth surfaces had we failed to clean out all of the courser grit between steps, but what appears to have happened is that the cerium oxide got into the natural fault lines in the rocks and opened them right up. The granite, which was incredibly smooth after the #600 silicon carbide, is bumpy from having large pieces come away. The quartz has deep grooves where there were once nice lines of colour. Now we wish we had skipped this stage and left them after the #600 silicon carbide. They weren't glassy and shiny, but at least they were smooth.
I'm sure there's a simple (and embarrassing) reason for this - could someone please fill me in?
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That is a mystery to me - I have never heard of this happening so hopefully others can help us out with an explanation.
Did many of the rocks have cracks or flaws? It is usually difficult to process rocks like this through to the end without running into some kind of problem? Although it is usually a contamination issue due to it being very difficult to clean the fissures of coarse grit completely so they can release it in a later stage and cause scratching.
Also fissures and cracks can mean the rocks are a lot more subject to cracking and breaking although it would normally occur randomly through the process - not solely restricted to the final polishing stage. Once you get some broken pieces floating around, there are sharp edges that can damage the rocks you have already smoothed with earlier stages.
There are other polishes you can try but I would be surprised if it is an issue with the particular polish being used.
Can anyone help with more specific advice on this - the problem described is a new one to me. Cracking and contamination would seem to be involved but there may be more going on as well.
cheers
Leah
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That was the mystifying thing for me, too, that it didn't happen randomly through the various stages. Aside from one or two rocks breaking during the first three stages, it all seemed to happen at the polishing stage. The most surprising ones were the chunks of granite, which were looking beautiful. They started off as naturally stream tumbled, rounded rocks and were getting beautifully smooth up until the last stage.
We're putting them through the burnishing stage, after which we'll decide which ones will need to be started over, but I'll try to get some photographs before we start tumbling them again.
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At this stage I'm interested in the 'few other odds and ends'. Can you be more specific?
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I suppose I'll have to photograph the lot and post some shots, for I'd be hopeless at identifying them.
If one of the rocks were significantly harder than the others, would it not wear at a different rate and therefore take longer to become smooth, and would it not crack the other rocks all of the way through the tumbling process rather than just towards the end? I suppose it's possible that one of the rocks was a conglomerate and some particularly hard fragments got knocked loose in the last tumble, pocking and gouging the other rocks.
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Welocme to the Forum crocdoc.
I have never tumbled stones before, so can't really be of much help. I do have a few questions though.
How are you washing your stones between grits? If it was me and mind you I know nothing about tumbling. I would wash the tumbler out, rinse the stones then put soapy water in the tumbler and then let them have a go for 24 hours between grits.
Also have you tried just doing them in batches of the same variety incase one is causing problems to another variety.
Gee hope that all made some kinda sense.
Take Care,
Deb beers
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Deb has some good suggestions - if you are being super careful on washing between stages, tumbling with soapy water for 12-24 hours can be a good way to really make sure you are getting all the grit out of the nooks and crannies. Just read that tip a few days ago while reading Steve Hart's book - Modern Rock Tumbling.
The other one is that perhaps I wouldnt be doing the rocks that seem to be a conglomerate. Some rocks just dont work well in the tumbler and a rock that is made up of different materials is going to be more liable to give you trouble. So sorting the rocks into different types might be worth the trouble.
cheers
Leah
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Mm, that's why I was wondrin what the other rocks might be.
I don't tumble, Muddy and Teddy tumble...
But I think I'd be making sure the hardness of the rocks are the same.
Also, I was wonderin whether it would be worth checking the stones every day in the final polish and whipping out the ones that are done. But Conglomerates generally are made up of differing hardness.
Also, just remember that even tho you might just put in say, quartz, each stone within that group will have it's own little quirks and makeup and how it responds to working, so I'd still check often.
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Thanks for all of the replies. I've got them out after the burnishing stage but ran out of time for a photograph or two. I'll still endeavour to do so tomorrow.
I'm beginning to formulate an answer, mostly based on the replies above. There's probably a little bit of a few things happening - leftover bits of grit from an earlier stage is a high probability, for I certainly didn't tumble with soap for 24 hours and the chances of grit hiding away in crevices is probably high. I think also I have been more inclined to notice the irregularities in the last stage because the pock-marks and rough patches contrast with the smoothly polished surfaces elsewhere on the same stones. The biggest disappointment, though, were these pieces of granite I collected in North Queensland. They had already been naturally stream tumbled when I found them (I was snorkelling at the time) and were polishing up beautifully through all of the stages but the surfaces on all but one seem to have crumbled in the polishing stage. They have broken along natural fault lines between the different coloured materials.
If I do decide to repolish some, I take it the best thing to do would be to sort them out by type and make up the rest of the space in the tumbler (since I will not have enough of each type of rock) with plastic beads?
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Okay, here are some photos of non-precious stones. Now that I've had time to look closely at them all, I think my main problem was a simple one of unrealistic expectations meeting reality. Many of the rocks are simply of a type that don't polish well. The ones that have crumbled would probably do that regardless. Also, I think I was comparing rocks which were examined straight after they'd been washed (and still had a slick of water on them, making them look more polished than they actually were), following an earlier stage of the tumbling process, with the same rocks after they'd been cleaned and dried, so the imperfections were more visible. There were definitely some rocks that waited until the polishing stage to develop deep pits or even partially crumble, but there are also quite a few that I know my god-daughter will be very pleased with and we'll probably try again with just a few of the others that I think still have a chance. I also suspect that some of the larger rocks were a bit too large and may have had a crushing effect on the others.
I imagine most people here concentrate on gems and this probably seems like a lot of fuss for some basic 'rocks', but it's a learning experience for my god-daughter and me.
Here's the whole lot, from both tumblers. If anything stands out as 'OMG those are so hard, you should NEVER put them in with other rocks', please let me know.
(http://www.pbase.com/crocdoc/image/123158062.jpg)
An example of one of the pieces of granite that appeared to crumble during the last stage (in the centre). It was perfectly smooth until I tried to polish it.
(http://www.pbase.com/crocdoc/image/123158093.jpg)
(http://www.pbase.com/crocdoc/image/123158100.jpg)
One of the stones that I don't think will ever polish. The dark veins are very hard and polish well, but the light coloured material in between has retained a granular texture. There were quite a few rocks like this in the pile - can anyone tell me what they are?
(http://www.pbase.com/crocdoc/image/123158107.jpg)
At the other end of the scale was this rock (I'm also clueless as to what it is). Grey and perfectly smooth. Another form of granite?
(http://www.pbase.com/crocdoc/image/123158111.jpg)
If I had to guess, these looked like fossilised bone to me when I first found them (it started as a single largish piece), but it has since occurred to me that it may be petrified wood. Any quick way to distinguish them?
(http://www.pbase.com/crocdoc/image/123158118.jpg)
It wasn't all doom and gloom. A few of the stones that did turn out alright.
(http://www.pbase.com/crocdoc/image/123158134.jpg)
(http://www.pbase.com/crocdoc/image/123158120.jpg)
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Where's Ted or Calx? they're the tumble info kings here.
Some of those look sweet as. I gotta go, will be back later.
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Looks like some of your finds came out nicely, but some just aren't going to ever polish. Experience will teach you the difference, keep trying. We put pieces of scrap leather about 1 1/2" [4 cm.] in rough dimension in our polish and post-polish soap runs, in an amount of about 20% of rock volume, makes nice padding. We keep separate leather for each process. Everyones success stories are different, the good part is being able to share them so easily on a forum such as this.
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Hi,
It looks like you tumbled at the polish stage with no buffering i.e. plastic pellets or leather strips. The slurry is very thin once you get to polish and if there's nothing to stop the stones bashing into each other, bad things happen (particularly if the stone composition is not cracked, not homogenous and moreso when the minerals in the stone are of different hardnesses).
As a general observation, granite is not a great choice for tumbling.
Here's what the stones should look like after a good polish session:
(http://aussielapidaryforum.com/forum/gallery/albums/Calxoddity_Album/Dir_1/thumb_main_736.jpg) (http://aussielapidaryforum.com/forum/index.php?action=gallery;sa=view;id=736)
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That makes sense and would explain why some stones seemed to develop chips and cracks only at the very last stage. After llarson's comment on the leather strips I had was starting to think about getting some plastic pellets (and putting fewer stones in) so there was more buffering.
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Don't know if you have sorted the problem yet, but an old book given to me said some of the methodology was always place rocks of similar hardness in tumbler and the polishing stage should be at a slower speed. I wash the final (600 grit) stage with a nail brush in a bucket of water and inspect whilst wet and again when dry for cracks or pitting. During the whole process I remove any rocks at each stage that seem unsuitable for the next stage, I put them aside and give them a second go next time around. This means you have a supply of rocks at various stages to make up for removed stones. I have always used tin oxide for polishing.
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u will nevever polish granite well that has large chunks of [soft-being the problem] biotite mica in it in a tumbler. also the red [looks like a quartz/jasper will come out better if u keep to the same rock in the batch[all the same hardness].cheers