Low-cost approach polishing small carbonate rocks and fossils by hand

[FranzBernhard]

Some of you may have noticed my flat polished fossils and fossil rocks. A few of you have some of them in their hands, e.g. @ricardo, @taj, @Monica, @fifbrindacier, @marguy

I lost access to the cutting, grinding and polishing facility recently. No great loss, but I still have some small specimens that I want to have polished. What to do?

 

I tried a low-cost, low-effort approach, using things I already have.

 

1. Cutting: I tried to cut some small specimens with an angle grinder. Well, it worked, more or less. Not the best option, don´t to it. Better would be a tile saw. They are cheap, far less than $100. But this is nothing for an apartment, I think. Getting a somewhat flat surface is the biggest problem of this low-cost approach. But see below.

 

Everything else is done on my usual desk!

 

2. Coarse grinding: No grinding machine here. I usually ground things flat on a diamond disk, followed by hand grinding with loose 600 and 1200 SiC (silicon carbide) grit. But I know, that limestone can be ground rather quickly by hand with SiC. Being on a low budget, what SiC should I buy? I bought SiC grit 400 (1 kg Euro 10.80,-) and SiC grit 1200 (0.5 kg Euro 14,40,-) from an Austrian supply house. What grinding plate should I use? Usually, steel plates are used. I don´ have any. But I have some glazed tiles. I was really surprised how well this worked. The SiC seems to be of very good quality and very "aggressive". A grinding time of to up to 10 minutes was enough to remove even bad scars from cutting with the angle grinder. 

Based on this experience, I tried to grind a small Favosites specimen without prior cutting. Worked very well, I got a flat surface of several cm² within 10 minutes.

 

3. Fine grinding: I used the same tile, cleaned it thoroughly, as well as the specimens (running warm water, brush). Only 2-3 minutes necessary to grind with 1200 SiC. Grinding worked well, but specimens had some fine scratches. I am not sure if this comes from outbreaks of the tile or if the SiC has some coarse grains admixed. Will try the bottom of a stainless stell pot instead of the tile. Seems a good option, but you should not be allergic to nickel...

 

4. Polishing: I have usually done this on a rotating felt disk, it took only about 1 minute for small specimens and up to 10-15 minutes for quite large specimens. Some years ago, I used a piece of jeans fabric for polishing a small piece of jet by hand - worked well. I scaled it somewhat up. Used the leg of a jeans, put a tile for some stability in it. I purchased Alumina for polishing from the same supplier (0.25 kg Euro 18.00,-). It works really well, but it takes some time, about 10 minutes for small specimens, about 20 minutes or even more for somewhat larger specimens. And don´t forget to clean your specimens after fine grinding!

 

5. Result: Quality of polished slabs is as good as usual (except some small scratches, not visible to the naked eye), but it takes much longer and large specimens would be a real pain.

 

6. Costs: No hardware bought. Purchased amounts of grinding and polishing medium will last for at least 100 specimens. So costs are less then 0.5 Euro per specimen.

 

Summing up: If you like to make a few small (< 5 cm) polished specimens of carbonate rocks (with fossils or not) or also e.g. jet, you can do this easily by hand on your desk with things you may already have at home. You need to buy some grinding and polishing medium (see above), though. And you need a somewhat flat surface to beginn with. Either naturally or a saw cut of some kind.

 

First row: Coarse grinding with 400 SiC on tile.

Second row: Fine grinding with 1200 SiC on tile.

Third row: Polishing with alumina on jeans leg.

Fourth row: Final results. To the right the specimens polished during the last two days (besides all my other commitments).

Franz Bernhard

[Tidgy's Dad]

Very interesting and useful. 

[ricardo]

47 minutes ago, FranzBernhard said:

 

Dear Franz,

 

I'm glad you found a solution for your magnificent work and for us to continue to see your beautiful polished specimens! 
Very instructive post!

 

Thanks

[fifbrindacier]

I'm sorry, i have difficulties to understand. I did use sandpaper to polish, beginning with the coarser and ending with the finer. Is that what SiC is, sandpaper ?

[daves64]

43 minutes ago, fifbrindacier said:

I'm sorry, i have difficulties to understand. I did use sandpaper to polish, beginning with the coarser and ending with the finer. Is that what SiC is, sandpaper ?

SiC = Silicon Carbide

Powder form used for flat grinding and polishing.

[FossilNerd]

Thanks Franz for posting this. I collected a few small coral specimens earlier this year with the intent to try my hand at polishing. I’ll give your method a try.  

[FranzBernhard]

6 hours ago, fifbrindacier said:

Is that what SiC is, sandpaper ?

I don´t know what grinding agent is used in sandpaper. There maybe some with garnet (maybe used for wood?), corundum (I think that is the most common) or even silicon carbide (SiC).

 

I have added "silicon carbide" to my original post. I am so used to the term SiC since nearly 30 years, so I thought, everybody knows it .

 

I am using the loose grit. This is the way it is most commonly done for flat surfaces. If you want to make only one polished specimen or irregular surfaces, sandpaper surely is the way to go.

 

Franz Bernhard

[fifbrindacier]

11 hours ago, daves64 said:

SiC = Silicon Carbide

Powder form used for flat grinding and polishing.

 

5 hours ago, FranzBernhard said:

I don´t know what grinding agent is used in sandpaper. There maybe some with garnet (maybe used for wood?), corundum (I think that is the most common) or even silicon carbide (SiC).

 

I have added "silicon carbide" to my original post. I am so used to the term SiC since nearly 30 years, so I thought, everybody knows it .

 

I am using the loose grit. This is the way it is most commonly done for flat surfaces. If you want to make only one polished specimen or irregular surfaces, sandpaper surely is the way to go.

 

Franz Bernhard

Thank you both for your lightings.

[taj]

Hi Franz 

 

Thanks for the post , very informative . I might use that ,since the club is closed since march ... 

On a side note , that reminds me that I have not posted some pics of the contest result ! Well , this has been a pretty s(%&%(&$ y  end of year  as a whole for me , but I will  take some time now with the season's holidays coming .

[FranzBernhard]

First of all, thanks to all of you for your appreciation!

 

I have tried two or three different things since Saturday. Maybe some of you might be interested, so I am tagging you all :

@Top Trilo, @taj, @minnbuckeye, @grandpa, @connorp, @LabRatKing, @KCMOfossil, @Brett Breakin' Rocks, @ricardo, @marguy, @Thomas.Dodson, @FossilNerd, @Tidgy's Dad, @Fossildude19, @Pagurus

 

1. Stainless steel pot:

Looked good at first sight, but the bottom turned out to be much to uneven. Got lot of scratches during fine grinding, much more than during grinding on the tile. The hypothesis that the scratches come from outbreaks of the tile can be dumped. So the 1200 SiC seems to be somewhat impure, but that´s not the main problem. It seems that coarse bits of grinding powder are caught in the shallow depressions or in the stamping of the pot and are later released again, resulting in scratches.

Pics show to the left the fresh bottom of the pot and to the right the bottom after coarse grinding of 3 specimens. Its clearly visible, that only an insignificant area has contributed to grinding - the dulled areas.

 

2. Back to the tile

No problem during coarse grinding, but more scratches during fine grinding. The tile was not flat from the beginning but looked somewhat similar to the bottom of the pot, though less extreme. And I had it already ground nearly smooth. But: I have also already ground away the glaze in some areas and exposed the ceramic base. And this ceramic is porous, catching also coarser grains, resulting in troubles like above. With carefully selecting "good" spots on the tile, I was able to get ok finely ground specimens, with some fine scratches, of course.

 

3. Glass plate

Beside steel plates, glass plates are often used as a base for hand grinding. I had that in my head since starting these experiments. But I don´t have a glass plate. Oh well, today it occurred to me, that I have some! Deep in the basement, recovered from the dumpsters about 15 years ago. They could be from a HiFi-tower. I have two narrow plates and a square one, 40x40 cm. And here we go:

Coarse grinding went very, very smoothly and after one specimen, the grinding surface was already totally dull (Second row). Fine grinding went also very smoothly, but still some minor scratches. These scratches are not remnants from coarse grinding. I have checked this out - The come and go during prolonged fine grinding. But that´s not a big deal. Polishing also went better after grinding on the glass plate.

 

Conclusion: You need a surface as flat as possible from the beginning. No problem during coarse grinding, but during fine grinding. Go for a glass plate; a piece of broken window glass could be ok. Well, don´t break your window, at least not in the northern hemisphere .

 

And here is the next batch of my hand-polished specimens, ground on the tile, except the specimen to the upper left. I have increased size somewhat, up to ca. 50 cm². It takes some time to polish these (about 30 minutes), but its ok if you are doing it only occasionally. Polishing cloth is still in very good shape after 14 specimens.

Franz Bernhard

[LabRatKing]

Just to add to this: another cheap source of flat, smooth surfaces is granite countertop stores. If you ask them, often they will just give you a broken piece. This can be an excellent alternative to a piece of glass!

[Phevo]

Thanks for a very nice post @FranzBernhard I remember polishing stones with my grandmother on glass when I was a tiny fellow ;P 

 

Perhaps your finer medium needs to be sieved, sounds like it may be contaminated with some coarser grains

 

(These days I am "polishing" stones in a rock tumbler and a few pieces of coarse medium in a fine medium has the same effect)

 

I don't think I have written this, but I have enjoyed watching your polished specimens, especially the snails so thanks again for sharing

[grandpa]

1 hour ago, LabRatKing said:

flat, smooth surfaces is granite countertop

I would avoid granite I think.  The large grain size of the granite offers up micro-gaps in the surface that will trap the grinding media (grit) and contaminate the sample as you progress to finer grits.

 

Here's some of what I (think I) know about the subject:

First thing is to get a good flat surface on the sample itself to start with.  A cheap way to approximate this is by use of a wet tile saw. 

 

From there (1st approach) I would go to emery cloth (a type of sandpaper that can be used wet) for polishing from say 80 grit to 600 grit.  You can wrap it over a sandpaper block use it to "sand" the stone if you want to do so instead of placing the emery cloth on the glass and moving the stone over the cloth.  I would then progress to SiC or AlO2 grits made for lapidary purposes down to at least 1200 grit; 2000 - 5000 if you want a glass polish.  For examples of these products see:

https://kingsleynorth.com/lapidary-equipment-supplies/sanding-belts-discs-rolls.html#q=&idx=kingsleynorthenglish_products&p=0&hFR[categories.level0][0]=Lapidary Equipment %26 Supplies %2F%2F%2F Sanding Belts_Discs_Rolls&nR[visibility_catalog][%3D][0]=1

and

https://kingsleynorth.com/lapidary-equipment-supplies/abrasive-media.html#q=&idx=kingsleynorthenglish_products&p=0&hFR[categories.level0][0]=Lapidary Equipment %26 Supplies %2F%2F%2F Abrasive%2C Polish %26 Media %2F%2F%2F Silicon Carbide Grit&nR[visibility_catalog][%3D][0]=1

from

https://kingsleynorth.com/

 

Critical to any polishing job is to ensure that the surface of the polishing base and the surface of the rock are thoroughly cleaned between changing grits.  Any contamination of grit from the previous process will result in a scratched surface.  Cleaning the rock surface is especially critical if the rock is porous or has cavities, as e.g. many rudists do.  Wash out the gaps, pores thoroughly and then repeat, and repeat, and . . .

 

Another approach, depending on how many samples you intend to work, is to save yourself much time and elbow grease by using a Bull Wheel type arrangement.  This is something that you can make yourself.  It consists of an arbor with a flat circular wheel https://kingsleynorth.com/aluminum-master-laps.html attached and the polishing media (e.g. emery cloth) attached to the flat surface of the wheel.  The arbor spins the wheel with the grinding/polishing media and you simply hold the rock to the wheel and let the friction of the spinning wheel do the job.  As you move from emery cloth to finer grits, a polishing pad is used to hold the various fine grits that you progress through.  Again, cleanliness of both the pad and the sample is essential between grits.  Ideally you will have a wheel/pad for each grit.  https://kingsleynorth.com/lapidary-equipment-supplies/polishing-heads.html#q=&idx=kingsleynorthenglish_products&p=0&hFR[categories.level0][0]=Lapidary Equipment %26 Supplies %2F%2F%2F Polishing Heads&nR[visibility_catalog][%3D][0]=1  While this costs more, it is much easier on the artisan if many samples are desired.  But wait! . . .

 

A third approach would be to buy the tool used to polish granite countertops.  It is typically a 5" diameter spinning wheel on a handle with a hookup for a hose and interchangeable 5" discs of increasingly finer grits.  It even comes with a 5" saw blade for trimming.  See e.g., https://www.amazon.com/marble-polisher/s?k=marble+polisher.

 

Whichever way you go, always be sure to work the stone in a wet setting to prevent lung damage from the dust (e.g., silicosis).  In the case of the bull wheel this means having a shield over the wheel that has a water spray.  https://kingsleynorth.com/lortone-splash-shield.html

 

I would suggest that the 3rd approach might be the most cost-effective for your needs, if you plan on doing many samples.

 

I am not in any way promoting any of the referenced products nor suppliers.   They are to be understood as examples to help in explaining what I am referring to for those who are not familiar with lapidary tools and processes.  There are other suppliers and products available.  The individual wishing to pursue this process will do well to do his/her own research on methods, products and suppliers.  This is only meant to be an introduction to provide awareness of some of the alternative methods for polishing the samples.  Others with more knowledge/experience than I will likely respond with better/more specific advice.  Until then, I hope this helps crack a window or two into the lapidary arts for those not familiar with the processes.

 

One final offering on the subject:

 

https://www.rockseeker.com/how-to-make-rocks-look-wet-and-shiny/

 

 

 

[Fossildude19]

Excellent post, with great information.  

[Bob Saunders]

I have polished the surface of Michigan datolites using pink Cerium ox-yd mixed in water and then onto a speed controlled leather wheel used for polishing of wood carving tools. I have not tried it but I have a GRS motor unit and diamond disks for sharpening hand engraving tools. For wood caring knives touch up I often use a piece scrap leather belt on a piece of wood  with green ZAM rubbed into it. Small datolites are attached to dop sticks or dowel rods diameter as needed. Dop is a green wax that is melted and pick up a touch then onto the stone. 

[LabRatKing]

1 hour ago, grandpa said:

I would avoid granite I think.  The large grain size of the granite offers up micro-gaps in the surface that will trap the grinding media (grit) and contaminate the sample as you progress to finer grits.

 

Here's some of what I (think I) know about the subject:

First thing is to get a good flat surface on the sample itself to start with.  A cheap way to approximate this is by use of a wet tile saw. 

 

From there (1st approach) I would go to emery cloth (a type of sandpaper that can be used wet) for polishing from say 80 grit to 600 grit.  You can wrap it over a sandpaper block use it to "sand" the stone if you want to do so instead of placing the emery cloth on the glass and moving the stone over the cloth.  I would then progress to SiC or AlO2 grits made for lapidary purposes down to at least 1200 grit; 2000 - 5000 if you want a glass polish.  For examples of these products see:

https://kingsleynorth.com/lapidary-equipment-supplies/sanding-belts-discs-rolls.html#q=&idx=kingsleynorthenglish_products&p=0&hFR[categories.level0][0]=Lapidary Equipment %26 Supplies %2F%2F%2F Sanding Belts_Discs_Rolls&nR[visibility_catalog][%3D][0]=1

and

https://kingsleynorth.com/lapidary-equipment-supplies/abrasive-media.html#q=&idx=kingsleynorthenglish_products&p=0&hFR[categories.level0][0]=Lapidary Equipment %26 Supplies %2F%2F%2F Abrasive%2C Polish %26 Media %2F%2F%2F Silicon Carbide Grit&nR[visibility_catalog][%3D][0]=1

from

https://kingsleynorth.com/

 

Critical to any polishing job is to ensure that the surface of the polishing base and the surface of the rock are thoroughly cleaned between changing grits.  Any contamination of grit from the previous process will result in a scratched surface.  Cleaning the rock surface is especially critical if the rock is porous or has cavities, as e.g. many rudists do.  Wash out the gaps, pores thoroughly and then repeat, and repeat, and . . .

 

Another approach, depending on how many samples you intend to work, is to save yourself much time and elbow grease by using a Bull Wheel type arrangement.  This is something that you can make yourself.  It consists of an arbor with a flat circular wheel https://kingsleynorth.com/aluminum-master-laps.html attached and the polishing media (e.g. emery cloth) attached to the flat surface of the wheel.  The arbor spins the wheel with the grinding/polishing media and you simply hold the rock to the wheel and let the friction of the spinning wheel do the job.  As you move from emery cloth to finer grits, a polishing pad is used to hold the various fine grits that you progress through.  Again, cleanliness of both the pad and the sample is essential between grits.  Ideally you will have a wheel/pad for each grit.  https://kingsleynorth.com/lapidary-equipment-supplies/polishing-heads.html#q=&idx=kingsleynorthenglish_products&p=0&hFR[categories.level0][0]=Lapidary Equipment %26 Supplies %2F%2F%2F Polishing Heads&nR[visibility_catalog][%3D][0]=1  While this costs more, it is much easier on the artisan if many samples are desired.  But wait! . . .

 

A third approach would be to buy the tool used to polish granite countertops.  It is typically a 5" diameter spinning wheel on a handle with a hookup for a hose and interchangeable 5" discs of increasingly finer grits.  It even comes with a 5" saw blade for trimming.  See e.g., https://www.amazon.com/marble-polisher/s?k=marble+polisher.

 

Whichever way you go, always be sure to work the stone in a wet setting to prevent lung damage from the dust (e.g., silicosis).  In the case of the bull wheel this means having a shield over the wheel that has a water spray.  https://kingsleynorth.com/lortone-splash-shield.html

 

I would suggest that the 3rd approach might be the most cost-effective for your needs, if you plan on doing many samples.

 

I am not in any way promoting any of the referenced products nor suppliers.   They are to be understood as examples to help in explaining what I am referring to for those who are not familiar with lapidary tools and processes.  There are other suppliers and products available.  The individual wishing to pursue this process will do well to do his/her own research on methods, products and suppliers.  This is only meant to be an introduction to provide awareness of some of the alternative methods for polishing the samples.  Others with more knowledge/experience than I will likely respond with better/more specific advice.  Until then, I hope this helps crack a window or two into the lapidary arts for those not familiar with the processes.

 

One final offering on the subject:

 

https://www.rockseeker.com/how-to-make-rocks-look-wet-and-shiny/

 

 

 

Oh, I agree with you! I should have been more clear. I use a section of granite countertop strictly as a base. It provides a flat, solid surface for the emery/polishing cloth/3M sheets as a sheet of glass would, nothing more. It is far too polished already to be of any use for polishing other stones. (It does work nicely for wet polishing with cerium oxide, but that is beyond the scope of this thread).

[Brett Breakin' Rocks]

4 hours ago, FranzBernhard said:

I have tried two or three different things since Saturday. Maybe some of you might be interested, so I am tagging you all

Thanks .... as I get settled here in Colorado I wanted to start building a prep lab and cutting and grinding intrigue me. The farthest I have gotten so far is using various grits of sand paper but this is an excellent alternative for a flat surface grind.

 

Cheers,

Brett

[FranzBernhard]

Thanks for all of your advice and experience! Its a very large field and my intention was to present a really low-cost approach with things you already have around, including some time. As every subject, its a deep rabbit hole; I have only shown one of the entrances to you. Other members have shown other entrances and have gone a lot deeper. Anyways, some kind of saw cut is nearly essential for such work. I have started a separate topic for this:

Low-cost rock/fossil sawing (TFF-topic)

 

Meanwhile, I have polished some more rocks and fossils. Now I am counting 20 home-polished specimens, some of them very small, just trying to grind something flat. I had also one "special" specimen, a breccia prone to breakouts. I did not stabilize it in any ways, I just wanted to try it as-is. It had a saw cut, though.

It went very well, not more scratches than the more stable specimens.

Thanks again for all your interest and the tips and advice.

Franz Bernhard

[fifbrindacier]

On 09/12/2020 at 2:23 PM, FranzBernhard said:

First of all, thanks to all of you for your appreciation!

 

I have tried two or three different things since Saturday. Maybe some of you might be interested, so I am tagging you all :

@Top Trilo, @taj, @minnbuckeye, @grandpa, @connorp, @LabRatKing, @KCMOfossil, @Brett Breakin' Rocks, @ricardo, @marguy, @Thomas.Dodson, @FossilNerd, @Tidgy's Dad, @Fossildude19, @Pagurus

 

1. Stainless steel pot:

Looked good at first sight, but the bottom turned out to be much to uneven. Got lot of scratches during fine grinding, much more than during grinding on the tile. The hypothesis that the scratches come from outbreaks of the tile can be dumped. So the 1200 SiC seems to be somewhat impure, but that´s not the main problem. It seems that coarse bits of grinding powder are caught in the shallow depressions or in the stamping of the pot and are later released again, resulting in scratches.

Pics show to the left the fresh bottom of the pot and to the right the bottom after coarse grinding of 3 specimens. Its clearly visible, that only an insignificant area has contributed to grinding - the dulled areas.

 

2. Back to the tile

No problem during coarse grinding, but more scratches during fine grinding. The tile was not flat from the beginning but looked somewhat similar to the bottom of the pot, though less extreme. And I had it already ground nearly smooth. But: I have also already ground away the glaze in some areas and exposed the ceramic base. And this ceramic is porous, catching also coarser grains, resulting in troubles like above. With carefully selecting "good" spots on the tile, I was able to get ok finely ground specimens, with some fine scratches, of course.

 

3. Glass plate

Beside steel plates, glass plates are often used as a base for hand grinding. I had that in my head since starting these experiments. But I don´t have a glass plate. Oh well, today it occurred to me, that I have some! Deep in the basement, recovered from the dumpsters about 15 years ago. They could be from a HiFi-tower. I have two narrow plates and a square one, 40x40 cm. And here we go:

Coarse grinding went very, very smoothly and after one specimen, the grinding surface was already totally dull (Second row). Fine grinding went also very smoothly, but still some minor scratches. These scratches are not remnants from coarse grinding. I have checked this out - The come and go during prolonged fine grinding. But that´s not a big deal. Polishing also went better after grinding on the glass plate.

 

Conclusion: You need a surface as flat as possible from the beginning. No problem during coarse grinding, but during fine grinding. Go for a glass plate; a piece of broken window glass could be ok. Well, don´t break your window, at least not in the northern hemisphere .

 

And here is the next batch of my hand-polished specimens, ground on the tile, except the specimen to the upper left. I have increased size somewhat, up to ca. 50 cm². It takes some time to polish these (about 30 minutes), but its ok if you are doing it only occasionally. Polishing cloth is still in very good shape after 14 specimens.

Franz Bernhard

 

On 12/12/2020 at 6:08 PM, FranzBernhard said:

Thanks for all of your advice and experience! Its a very large field and my intention was to present a really low-cost approach with things you already have around, including some time. As every subject, its a deep rabbit hole; I have only shown one of the entrances to you. Other members have shown other entrances and have gone a lot deeper. Anyways, some kind of saw cut is nearly essential for such work. I have started a separate topic for this:

Low-cost rock/fossil sawing (TFF-topic)

 

Meanwhile, I have polished some more rocks and fossils. Now I am counting 20 home-polished specimens, some of them very small, just trying to grind something flat. I had also one "special" specimen, a breccia prone to breakouts. I did not stabilize it in any ways, I just wanted to try it as-is. It had a saw cut, though.

It went very well, not more scratches than the more stable specimens.

Thanks again for all your interest and the tips and advice.

Franz Bernhard

That's a great job Franz, it's beautiful.

[cngodles]

On 12/9/2020 at 12:50 PM, LabRatKing said:

third approach would be to buy the tool used to polish granite countertops.  It is typically a 5" diameter spinning wheel on a handle with a hookup for a hose and interchangeable 5" discs of increasingly finer grits.  It even comes with a 5" saw blade for trimming.

I’ve used these for polishing limestone on a Dewalt Angle Grinder. It’s dusty work and takes time, but the finished polished stone looks nice. And no water!