Tumbling beach and landscape rocks - Bad yields

[gnuuser]

Hi, all.

I’ve been tumbling for about 9 months. I’ve made some beautiful rocks, but I’ve also made a lot of duds. I’m trying to increase my consistency, and improve my yields. My problem is that I often get about 1/4 beautifully polished rocks and about 3/4 unpolished or barely polished rocks of the same type in the same batch.

I use mostly beach and landscaping rocks because I just want volume. I am not too particular about the type of rocks I polish, so it doesn’t make sense for me to spend lots of money buying rocks online (although I have bought some, and those have always come out beautifully). I strongly suspect that I’m not removing enough of the weathering rind from the rocks, so the ones that have less rind polish up nicely and the others don’t. Before I learned about weathering rind, I was starting these rocks in medium grit. I just started over with a new batch, and I’m going to put them through at least two weeks of coarse grind to make sure the weathering rind is gone.

Just a little about my tumblers. I originally built a home-made tumbler with two Lortone 12 lb. barrels and three Lortone 3 lb. barrels. That machine eventually broke, so I bought the Lortone machines, and now have two Lortone QT12, two Lortone 33B, and one Lortone 3A. You’d think that I would be swimming in polished rocks, but I only produce a tiny amount of good rocks and a lot of bad rocks out of every batch.

Any advice and guidance would be much appreciated!

[gnuuser]

Here are some photos for context.

The upper left photo shows the landscaping and beach rocks I gather.
The upper right photo shows the same kind of rocks after 2 weeks in coarse grind.
The lower left photo shows the bulk of my results... partially polished or unpolished rocks.
The lower right photo shows the successes. Same rocks in the same batch. Some come out great, some don't.

The detail photo shows a single rock that polished in a couple of places, but not others!

UPDATE: No, these are not the same rocks. They are representative of the kind of rocks I've been tumbling and what they look like at different stages. I have tried identifying different types of rocks uisng pictures online, but it's pretty hopeless for me. Unless they come in a bag labeled "AGATE," or "JASPER," I have no idea what they are. The one exception is the big, white one that I'm reasonably sure isn't jade. Actually, I'm also fairly certain that two of the pieces in the lower right are petrified wood.

 

[captbob]

2nd photo... rocks from the same batch, but NOT the same rocks!

Some rocks will give you no better than a matte finish no matter what wizardry you throw at them.
Nature of the beast.

You did nothing wrong. Some rocks will shine and some won't.

carry on!

[fernwood]

The last one looks like sugar quartz. That does not polish well.
Looks like some granite in the group photo. How that polishes depends on the composition. Some is great and some not so much.

Keep experimenting. Learn about what types of rocks polish well.
Above all, have fun.

[gnuuser]

So, if I want better yields, I need to stop being so cheap and buy better rocks?

[pauls]

Some polish some don't.
Anything grainy or pitted probably will be difficult. If you hit one with a hammer and it breaks with a nice smooth face, not grainy looking then it could be OK, as long as it's hard enough.
Go for rocks about Quartz hardness, so if a piece of sharp quartz scratches it easily then it will be too soft.
Soft rocks such as Obsidian, Fluorite etc are really difficult, not impossible but they require special techniques to get a good result.

As for buying rocks, that's one way of getting them but boy it's fun to get out in the wild somewhere and find your own.

[Rockshund]

One thing that hasn't been mentioned is that all the rocks in your batch need to be about the same hardness. If you are picking rocks on the beach, some will be softer than others. Do what you can to ensure the rocks are of similar hardness. Scratch test or identify the rocks. Coarse-grained rocks will often have grains that differ in hardness which are harder to polish.

[hnhstngs]

Aug 4, 2019 13:56:51 GMT -5 gnuuser said:

So, if I want better yields, I need to stop being so cheap and buy better rocks?

The biggest advantage to purchasing material to tumble is you'll know exactly what you are starting with.  Self collecting rocks and tumbling them without knowing what they are is a crap shoot, some will turn out fine and others won't.  If you want to keep using self-collected stones I'd suggest limiting your collecting to rocks of the same type you've already had success with.  Looking at your pictures its clear that while the stones may have come from the same area they are not the same material.

My largest drums are 6 lb and I noticed a marked increase in rough tumbling efficiency when I started using using very coarse grit for the initial stage.  With your 12 lb barrels you might try using at least 45/70 SiC or even 30 or 36 grit for your first stage.  The bigger barrel load will easily breakdown the grit.  I would add something to thicken the slurry right away though as suggested by jamesp.  Using clay will help keep the larger grit in suspension right from the start of the tumbling run (I usually add 1/3 c of the cheapest cat litter I can buy to a 6 lb barrel).

[gnuuser]

Thanks much for the suggestions, everyone. It's clear from your comments that most of the rocks I'm using just won't polish, no matter what, so I'll need to be more selective. I've been assuming that I could get most rocks to polish if they were hard and small-grained, but that may not be the case. Where I have bought rocks, they have always come out very well, so it's obviously my choice of rocks that's the big problem, which is very helpful.

Thank you!

[gnuuser]

So, based on the advice I've received here, I did some more reading about rock types and identification and made some changes that I think will help.

As I understand it, the majority of rocks that will take a polish are various forms of micro-crystalline quartz (technically chalcedony). There are many of them, and they go by lots of names, the most common in rock tumbling are many different types of agate and jasper. With that knowledge, I am now picking out only rocks that are hard (can't be scratched with the nail file on my pocket knife) and have no discernible grain. I rub them with my thumb and scratch them with my fingernail. If there's any sandpapery feel to them at all, I leave them. I can see that the rocks I'm picking up now are qualitatively different to what I was accepting before. They feel "glass-ier."

I don't think this idea is fool-proof, but it should net me 3/4 good polished rocks, instead of 1/4 good polished rocks, which I would be happy with for now. I'm not 100% confident because some rocks with a large crystalline texture can take a good polish (e.g., marble, quartz), and I don't quite understand the dividing line. It might be that all crystalline rocks can take a polish (except for some forms of granite, which have grains of different harnesses), but that rocks without a crystalline texture (most beach rocks) must have no discernible grain.

In any case, I'm still picking up rocks from the ground because a) they're everywhere around here, and b) I like finding them. However, I went to Home Depot and found at least 3 bags of landscaping rocks that should work, and they're cheap... $10 for about 40 pounds. The first is a bag of Ash River black rock that is hard and has no discernible grain (2-3 inches, which is the size I like). The second is a bag of Imperial Beach river rock, which is the same, but in earth tones. The third is a bag of marble chips. I've never tumble marble, but I understand that it's soft (harder to tumble) and takes a good polish. At roughly $10 for 40 pounds, I have tons of consistent material to experiment with, and should be able to produce lots of tumbled rock.

[gatorflash1]

Some good advice about a problem that all tumbler newbies have encountered. The frustration I have is that even when I order what are supposed to be good solid agate rough rock I usually end up throwing a third of the order into the trashy rock pile because it is so cracked or pitted that it is not worth the time and money it costs to try to get a decent tumbled rock appearance from it.


If after about two step 1 tumblings the rocks don't appear to be taking some shine I toss them into the crappy rocks pile, not wasting time and money for grit and polish that will never work.

[jamesp]

Looks like lots of granitoids gnuuser. If you master a high polish on granite please share your recipe !

[Fossilman]

Yuppers, granite is hard to polish and a few others, like sugar agates and etc.. I keep notes in a book on my tumbles, helps out a bunch on what to tumble and not to tumble and the why's and don't on certain material... Keep on rolling and it all will become natural to you in the long run!

[gnuuser]

Aug 15, 2019 6:33:51 GMT -5 jamesp said:

Looks like lots of granitoids gnuuser . If you master a high polish on granite please share your recipe !

I think you're right. What I've been collecting in the past couple of weeks is significantly different from what's shown in the picture. I'm doing it by feel (no discernible grain or grit), and am realizing that seems to exclude granite. I wouldn't have recognized granite a couple of weeks ago, but now I think I'm getting it.

[jamesp]

Aug 15, 2019 11:07:36 GMT -5 gnuuser said:

Aug 15, 2019 6:33:51 GMT -5 jamesp said:

Looks like lots of granitoids gnuuser . If you master a high polish on granite please share your recipe !

I think you're right. What I've been collecting in the past couple of weeks is significantly different from what's shown in the picture. I'm doing it by feel (no discernible grain or grit), and am realizing that seems to exclude granite. I wouldn't have recognized granite a couple of weeks ago, but now I think I'm getting it.

Try to stay away from felspar. It is in granite. Felspars being attractive are a teaser but are difficult to tumble with good results for a Mohs 6 rock.

[gatorflash1]

You might want to try some Chrome Oxide Polish, used for granite, marble, etc.

rocktumbler.com/blog/polishing-igneous-and-metamorphic-rocks/

[gnuuser]

Aug 29, 2019 9:18:41 GMT -5 gatorflash1 said:

You might want to try some Chrome Oxide Polish, used for granite, marble, etc.

rocktumbler.com/blog/polishing-igneous-and-metamorphic-rocks/

Thanks. I'll give that a try. I've only been using aluminum oxide polish.

[gatorflash1]

I would suggest using their recipe as well.

rocktumbler.com/blog/polishing-igneous-and-metamorphic-rocks/



How Well Did They Tumble?



"The rocks that we picked were mostly granite, granite gneiss, gabbro, diorite, and basalt. We placed them in a Thumler's UV-10 tumbler with about 50% ceramic cylinders, six ounces of 150/220 silicon carbide grit, plus a little water and ran them for three days (they were rinsed and fresh grit added each day). We then ran two days in 500F grit and two days in TXP polish with a couple shots of Dawn "Direct Foam" detergent (the Dawn provided bubbles that we believe provides some cushioning during the polishing step.



We ended up with a lot of beautiful polished stones. Check out the granite, granite gneiss, basalt and diorite in the image above! A few of the rocks in our batch didn't want to polish. That's OK, we got a lot of nice ones.



Happy Tumbling! "

[gnuuser]

Aug 30, 2019 14:01:52 GMT -5 gatorflash1 said:

I would suggest using their recipe as well.

rocktumbler.com/blog/polishing-igneous-and-metamorphic-rocks/

Someone else suggested that page previously. Other than the fact that they're using a vibratory tumbler for polishing (which I don't have and don't want to buy), I was pretty well using their recipe. I used 500F to pre-polish, and 1200F aluminum oxide to polish (their TXP is aluminum oxide). A few of mine kinda-sorta polished, but most didn't.

[Wooferhound]

Look closely at the Other Rocks in the batch that did not polish. Check for sharp cracks, broken and Sandy rocks. Those will be the ones that are scrubbing the polish off of the good rocks in the batch.