richardh
spending too much on rocks
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Post by richardh on Jul 27, 2016 11:22:17 GMT -5
I have been working for weeks on my second batch of rocks (the first batch was a failure) and am still running into come challenges that I would like some help with. I believe this rock is some sort of jasper. I collected it from the bank of the Brazos River in southeast Texas near Houston. I had tumbled it with 46-70 grit SiC for about two weeks and I never seemed to be able to get rid of all of the scratches and fishers. After reading on these forums about someone using a tile saw to shape rocks I decided to give it a try with the tile saw we had in the garage. I went around and cut away all of the parts of the rock with visible scratches, cracks, fishers… and ended up with a rock that was more or less flat on all sides. I tumbled this for an additional week in the 46-70 grit SiC and ended up with a rock that I was very excited about. Everything looked pretty smooth and the edges were nicely rounded giving pretty much the shape you see here. I then tumbled this rock with a bunch of similar rocks with 120-220 grit SiC for a week that ended this morning. When I checked the rocks pretty much all of them came out looking like this. New cracks were visile, lots of pitting and chips… I thought I was being fairly gentle. I am using a Harbor Freight 3lb tumbler which has a rubber barrel and I used the following formula when starting the 120-220 stage. 1.5lb rocks 0.5lb small ceramic media (they had already been broken in during my first batch) 1.5 tbsp of 120-220 Sic (purchased from Rockshed) Water up to the level of the top of the rocks in the barrel. The barrel was about ¾ of the way full and when I turned it in my hand it sounded like the rocks had plenty of room to roll across each other. When I opened the barrel this morning the grit all seemed to be broken down into very fine powder. When I felt it with my finger tips there was not any gritty feel at all. Here are a couple of photos of what the rocks look like now when dry. I did have another rock that I found on a trip to California a couple of years ago. I am not sure what it is but it seems to be suffering even more from this last stage. Here are a couple of sample images of it: Can anyone identify what I am doing wrong or suggest anything that might help yield better results? Is the problem simply that the quality of my rocks is so poor that I am just revealing imperfections that were always there and I need to find a better quality feedstock? I do have some agates going in a second tumbler and I understand that they might be easier to tumble but they still appear to need lots more time in the course stage. I may be misidentifying what I am trying to tumble but I was under the impression that jasper was relatively easy to tumble. Thanks for any help you might be able to offer.
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huskeric
spending too much on rocks
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Post by huskeric on Jul 27, 2016 13:32:46 GMT -5
Not being an "expert," what I would say from what I have learned, I would guess that on your first pic, the rock has some pretty deep pits in it, and you are making them smaller, but you would be better off if you pre-shaped the rocks with a diamond wheel. I have both a Dremel with some diamond bits for small rocks and an angle grinder with a diamond blade for my larger rocks. I try to shave them down and remove as many of those imperfections as possible before putting them in the tumbler. Often times, I find that some of the pits, etc. are much larger than I originally thought, and at that point you have to decide if it's even worth trying to polish.
On your second rock, I can't tell you what material it is, but I would say that at least the banding in the rock is significantly softer than anything else you have in the tumbler, and it is getting cut away at a much higher rate than everything else. I *believe* that is called "undercutting." I think that for those stones, you either need to start with a finer grit, polish it with other softer stones, or save it for hand-polishing.
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richardh
spending too much on rocks
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Post by richardh on Jul 27, 2016 21:15:17 GMT -5
Thank you very much for taking the time to reply. With both of these rocks I did use a tile saw to cut off all of the imperfections. Basically I went around and any surface that had deep scratches, chips, pits… and shaved them down little by little until they were smooth. The result was rocks that looked smooth but had a bunch of flat faces. When I put them back into the coarse grit until the flat faces were rounded and the rocks were smooth overall.
I was very pleased at this point because it looked like I would be able to save a lot of time in the coarse stage. I took the fully smoothed rocks and cleaned them twice with dish detergent along with the media and barrel and then started a 120-220 grit stage. After a week in this stage I got the results you see here.
Being a beginner I don’t know if I did everything correctly but I think the hardness is at least around 7 because I was able to scratch neither with an iron nail. That was basically the test I did to determine what would be appropriate to put in the tumbler. If a nail could scratch it, it didn’t go in.
The black rock seems to cleave in one direction. I think it might be some sort of beryl. I think I found it near San Diego, CA but it was a long time ago and I am not totally sure about that.
Anyway, I suspect the problem with the black one is the cleavage. I did notice it when I was cutting it with the saw. I found it difficult to get smooth surfaces because pieces kept chipping off and at one point a large portion of the rock just sort of flaked off.
Does anyone know if this type of material is possible to tumble successfully?
On the red rock I think the problem might just be that the rock is of low quality and has little bubbles or cavities throughout. I guess I am trying to say that the rock is sort of porous and no matter how much I wear it down I will constantly expose new cavities.
However, I am not sure that the rocks (particularly the red ones) aren’t getting damaged from crashing into each other and the tumbling action is just too harsh for these rocks. I thought that adding small ceramic media would help avoid this but I don’t know if that is the case or not.
My plan at this point is to throw the red rocks back into the coarse stage and keep grinding them down and see if I can get them smooth again. I think the black rock is beyond my skill level at this time and I will just set it aside until I learn more.
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quartz
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Post by quartz on Jul 28, 2016 0:15:30 GMT -5
Looks to me, you started out trying to tumble a couple rocks that are full of flaws clear through. Try running pieces that are visibly solid on the outside, pits and cracks often go very deep.
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Post by pauls on Jul 28, 2016 2:26:23 GMT -5
I agree with Quartz. I don't think you are doing anything wrong apart from tumbling rocks that are full of cracks and holes. That Jasper is nice and could make a reasonable rock by grinding (or sawing) the pitted end away.
Paul
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jamesp
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Post by jamesp on Jul 28, 2016 6:11:29 GMT -5
I 4th
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richardh
spending too much on rocks
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Post by richardh on Jul 28, 2016 8:27:21 GMT -5
Thanks for the help everyone, I will try to grind it off and give it another try.
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Post by Peruano on Jul 28, 2016 10:09:58 GMT -5
Those don't look like pits that you would have started with, and you say that you are seeing new pits and cracks. I'm a vibe guy, not a rotary, but I'm tempted to say that you are producing some of the damage by too violent action and perhaps too coarse sized grit for the hardness of the stones. That hematite jasper (the red one) is quite variable as to hardness and can give problems. The black stone (unknown to me), but it does have veins of something else running through, seems to be prone to undercutting where the two types of materials come together. So . . I'd listen to the above advice but also think about going easier on coarse grit and being selective about uniformity of rocks and uniform hardness as much as possible until you get the hang of what will tumble and what will disintegrate. Grinding may save the red jasper, but it still will be necessary to tumble with like minded stones. Things to consider.
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richardh
spending too much on rocks
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Post by richardh on Jul 28, 2016 14:17:19 GMT -5
Peruano,
This is what I was suspecting. When I look closely at the jasper it appears to be many layers of differing consistency. I guess this makes total sense based on my understanding of how jasper is formed. That top part of the rock appears to be a softer material. After I read your reply I went back and tried scratching it with a nail and I could barely scratch that section and the other parts of the rock would not scratch. When I have a little time I will grind that part of the rock away and throw it (and the other similar rocks that are in the tumbler) back into the coarse grit for a while then try again. I think I might need to find some better rocks. If all goes as planned I will make a trip to the San Jacinto river this weekend and hopefully find some good specimens.
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Mark K
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Post by Mark K on Jul 28, 2016 15:25:13 GMT -5
You could try regrinding the red one and running it with other rocks of similar hardness running 60/90 instead of the really course stuff you were running. I wouldn't bother with the black one. also fill your barrel by weight with a scale if you can. Since you are a newbie, this will help considerably. Put the grit in first, them put what you think is the right amount of rock and then put the water in. If it is over, take a rock or two out, if under, add.
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richardh
spending too much on rocks
Member since June 2016
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Post by richardh on Jul 28, 2016 15:40:24 GMT -5
Thanks very much for the advice. Yes, I have been using a scale to weigh in the rocks. Most of the rocks in the barrel now are red ones just like the one in the photo. There are a few other rocks but the majority are all the same. I don't believe I have any 60/90 left but the problems started showing up when I put the rocks in with the 120/220. It is raining at the moment so my grinding will have to wait since I must do the work outside.
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Mark K
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Post by Mark K on Jul 28, 2016 18:01:44 GMT -5
You better believe it.
One you don't want to breathe that stuff so outside in the wind is best.
And
Two your wife would cut your nuts out if you made dust like that in the house.
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Deleted
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Post by Deleted on Jul 28, 2016 19:40:53 GMT -5
5th unless someone else did already, then just add me to the end.
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Deleted
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Post by Deleted on Jul 28, 2016 19:42:18 GMT -5
Google "leaverite".
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richardh
spending too much on rocks
Member since June 2016
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Post by richardh on Jul 28, 2016 20:11:13 GMT -5
Thanks for the leaverite term, learned something new (and funny). I sent the picture of the black rock to my friend who is a geologist and he thought it might be tourmaline. Anyway, I am going to hang onto it because I think it is a cool rock but probably not so much for tumbling.
-Makr K Yes, definitely don't want to breath the dust. I have been wearing a mask when I cut the rocks. I don't have a wife yet but my mom would kill me if I ran that saw in the house or garage.
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Deleted
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Post by Deleted on Jul 28, 2016 23:39:43 GMT -5
Schorl is a mohs 7. Try to scratch thr black one with an agate or jasper.
Report back here
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jamesp
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Post by jamesp on Jul 29, 2016 4:49:01 GMT -5
If the black rock is light weight it may be coal. Good quality jasper and other well formed agates are slow to shape. And have few cracks or pits. Not likely to be damaged by your tumbler. You can add a couple of pieces of thick glass or obsidian in with your tumbles. They are somewhat fragile and tell you if your tumbler is damaging your rocks. The red jasper posted has a lot of damage from weather or malformation on one side where the pits and cracks are. That pitted area could be ground off with a tile saw and that would probably solve the problem on that particular tumble. Lots of river worn pebbles can have such damage. This is coral that I break into pieces. It has few flaws/pits/cracks. Very hard and takes a long time to coarse grind. But a good candidate for tumbling.
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jamesp
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Post by jamesp on Jul 29, 2016 5:11:49 GMT -5
Coral looks like this before being tumbled. Almost like glass. These were probably 2-4 pound chunks each that were careful broke up with a hammer. This may be as good as it gets for in terms of mechanical properties for tumbling.
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richardh
spending too much on rocks
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Post by richardh on Jul 29, 2016 11:13:07 GMT -5
Schorl is a mohs 7. Try to scratch thr black one with an agate or jasper. Report back here If I really bear down on it quartz will barely scratch it. I couldn't really get it to scratch the quartz. I think it is slightly softer than Quartz.
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richardh
spending too much on rocks
Member since June 2016
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Post by richardh on Jul 29, 2016 11:17:44 GMT -5
jamesp I have been grinding on some of the jasper pieces this morning and I think you hit the nail on the head. I just don't think it is very well formed material. Some of the pieces are looking OK with few or no pits and most of them seem to be porous. As I keep grinding I find more cracks and cavities. It is difficult to accept even though it is obvious. Not all material is equal. It is difficult to give up on rocks that I thought would be neat looking but the reality is that most of my rocks probably never will make good polished specimens. I just need to set the lower quality ones aside and seek out better quality ones.
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