Directions for Turning Rough Rocks into Beautiful Gemstones
Using a rock tumbler to convert rough rock into sparkling gemstones is part art and part science. There are many ways to obtain great results and there are also many ways to produce inferior results. We are writing this to share the method that we currently use after experimenting for several years. Perhaps our method will work for you too, or you might experiment and find even better ways to tumble. Don’t hesitate to experiment. Trying new things is the only way to improve and a great way to learn.
There are three important rules that you should keep in mind whenever you go to your tumbler. These are: 1) “Garbage in means garbage out” 2) “Avoid contamination” and, 3) “Great results take time.”
“Garbage in means garbage out” -- If you start with garbage (low quality rough) you should expect low quality gemstones. So, don’t hesitate to discard a rock that is porous, break a fractured rock into smaller pieces, or discard a rock that will not produce an attractive tumble. You will spend a lot of time and valuable supplies tumbling a batch of rocks. Using quality rough saves time and gives you better value for your money.
“Avoid contamination” -- You will use a different size abrasive grit for each step of the tumbling process. If coarse grit gets into your fine grit step it will scratch up the rocks and you will need to do the fine grit step over again. So be sure that you thoroughly clean the rocks, the tumbler barrel and your tools when you change from one grit size to another.
“Great results take time” -- Don’t be in a hurry. Spend time doing a great job. If you tumble a batch of rocks through the coarse grind and they still have a few rough edges or are not nicely rounded, don’t hesitate to run them through that step again. Also, spend the time needed to thoroughly clean your work area, tumbler barrel and tools between steps to avoid contamination.
Inspecting Your Rough
“Garbage in means garbage out” -- Begin with high quality rough and you have a chance to produce high quality gemstones. We prepare to tumble by dumping out our rough rock and looking at each piece. Porous pieces will not make nice tumbled stones and they will carry grit from one step to the next. We discard them. Rocks that are fractured will break while tumbling and scratch other rocks in the batch. When we see a fractured rock in our rough we break it into smaller pieces that are fracture-free. If we find rocks that will not produce a nicely shaped tumble we break them to make smaller stones that will shape nicely.
For best results your tumbler barrel should be loaded with rocks of mixed particle size (from about 1/4 inch up to about 1 1/2 inches in diameter). If you have only small material that’s OK… just follow the instructions below. However, if you only have large rocks then you should add some smaller material (small rocks are needed to carry grit to all of the surfaces of the larger rocks). If you don’t have smaller material you can break a few of the less desirable large rocks into smaller pieces, or, add some small ceramic tumbling media to get smaller particles into the load. For best results any load that you tumble should have at least 25% small particles.
Finally, tumbling works best when all of the rocks in the barrel are about the same hardness. If you tumble soft rocks with harder rocks the softer stones will wear away quickly.
Loading the Tumbler Barrel
Before you load the tumbler barrel be sure that it is perfectly clean. There should be no grit left in the barrel from a previous batch. To prevent leaks, the rim of the barrel and the lid should be totally free from grit or rock particles.
Protect your eyes! Wear safety glasses when working with rocks, grit and tumbler slurry or when opening tumbler barrels.
Once you have a clean barrel add enough rock to fill the barrel about 1/2 to 2/3 full. (If you add more or less the rocks will not tumble properly.) If you don’t have enough rough to fill the barrel at least 1/2 full you can add enough ceramic media to bring the barrel up to a proper operating level. Finally, add enough water to fill the barrel to just below the top of the rocks.
If you are tumbling with the Thumler's Model MP-1 tumbler you can follow the instructions below but use about two level tablespoons of grit or polish in each of the tumbling steps (Step 1 through Step 4).
We strongly advise keeping records of what you tumble, the amount of time and the results that you obtain. It is easy to forget what day you started the tumbler or what type of grit was used. Keeping records will keep you on track and provide a history that will help you learn. We record material tumbled, start date, abrasive used, media used, finishing date and duration, along with any comments about the results and observations.
To help you with your record keeping we have prepared a printable tumbling log.
STEP 1 – Coarse Grind
The first step of the four-step tumbling process is to run the rocks in the tumbler with coarse grit. You begin with a barrel that is 1/2 to 2/3 full of tumbling rough, then add water until the water line is just below the top of the rocks. Now add two level tablespoons of coarse grit (we use 60/90 grit silicon carbide) for each pound of rock. Seal the barrel and run for about seven days.
At the end of seven days open the barrel. You will find a barrel of muddy water! Dump the contents into a screen or a colander over a plastic bucket and rinse off every speck of grit and mud.
Wear safety glasses to protect your eyes from a splash of mud.
DO NOT ALLOW THE GRIT OR MUD TO GO DOWN THE DRAIN – it will clog the pipes. To avoid getting grit and mud down the drain we wash the rocks in a colander over a plastic bucket.
Now that you have washed the rocks it is time to inspect them. You want to determine if they are ready to move on to STEP 2 or if another week in STEP 1 would improve their appearance. We sort the rocks into four categories:
A) those that are ready for STEP 2;
B) those that could be improved by another week in STEP 1;
C) those that should be broken or trimmed and returned to STEP 1; and,
D) those that should be discarded.
We then repeat STEP 1 until we have enough nicely-shaped rocks that are ready for STEP 2.
STEP 2 – Medium Grind
The second step of the four-step tumbling process is to run the rocks in the tumbler with fine grit. Before you begin it is extremely important to clean all of the coarse grit from the rocks, from the tumbler barrel and from the barrel lid. It is very important to avoid having a few grains of coarse grit in the fine grind step.
Again, fill the barrel 1/2 to 2/3 full of rough (if you don’t have enough rough use plastic or ceramic media to make up the volume), add water until the water line is just below the top of the rocks, add two level tablespoons of medium grit (we use 110/220 grit or 150/220 grit silicon carbide) for each pound of rock, and tumble for seven days.
At the end of seven days open the barrel and clean all of the grit from the rocks, barrel and lid (don’t let any grit go down the drain). At this point in the tumbling process a dry rock should have a smooth frosted surface.
Inspect the rocks, looking for any that are cracked or broken. If found they are discarded or saved for the next time we run Step 1.
STEP 3 – Fine Grind / Pre-polish
The third step of the four-step tumbling process is a week in a fine grit or pre-polish such as 600 grit or 500 grit silicon carbide. Begin with a barrel that is perfectly clean. Add rough to fill it 1/2 to 2/3 full, add water up to just below the top of the rocks and two level tablespoons of fine grit per pound of rock. Run this for about seven days and then do a thorough cleaning of the rocks, the barrel and the lid. Remove any rocks that have broken or show signs of fracturing. At this point in the process, the rocks should be extremely smooth and some of them might start to have a slight luster.
STEP 4 – Polish
Now you are down to the final step – the one that will determine the quality of your polishing job. Be sure that the rocks and the equipment are perfectly clean. (Some people have an extra barrel that they use only for the polishing step.) A few specks of grit could ruin a great polish.
Place the rocks in the barrel, add water to just below the level of the rocks, add two level tablespoons of rock polish (we use aluminum oxide powder or TXP) per pound of rock. Close the barrel and run for about seven days.
When you finish this step your rocks should be bright and shiny. If they are, congratulations! Admire them for a while and share them with your friends.
If the stones have an extremely smooth surface but do not shine they might need cleaned up using the burnishing step described below. If they have scratches on them then you will need to go back to STEP 2 and repeat the medium grind, fine grind/prepolish and polishing steps.
Sometimes our stones are a little "hazy" when they come out of the polish or small particles of polish are in micro-size crevices. We shine and clean them up by tumbling for a couple hours in soapy water. This is called "burnishing".
To burnish we place the stones in our polish barrel with the normal amount of water and then we add about one tablespoon of chopped “Ivory” bar soap for each pound of rock (we use plain “Ivory” soap – don't use a soap with aloe or abrasive or any other additive). This burnishing step always makes the tumbled gems a little brighter and sometimes it really kicks up the shine.
We hope that you enjoy rock tumbling. If you have some success please feel free to send us a photo of your favorite tumbles. We also welcome questions about tumbling equipment, supplies and procedures. email@example.com
Working to transform rough rock into sparkling gemstones gives most people a great feeling of accomplishment. It doesn't matter how old you are or how many batches of rock you have tumbled in the past - the reward is there every time!
Tumbling will enable you to turn the rough rock on the left side of this photo into the sparkling gemstones on the right side of the photo. Amazing!
"Garbage in means garbage out." The rocks in this photo do not have the potential to become nice tumbled gems. A rock with voids should be thrown away - the voids will trap grit and contaminate your prepolish and polishing steps. Protrusions can be broken off - and that might yield two nicely rounded rocks. And, fractured rocks might be broken to yield smaller fracture-free pieces. Always wear gloves and safety glasses when breaking rocks.
When loading the tumbler barrel you should have pieces of rough with a range of particle sizes. We would mix the above sizes together in the barrel. If you load the barrel with a few large pieces there will be very few points of contact between the rocks in the load. Those points of contact are where grit is trapped between the rocks and where grinding occurs. If you have lots of small pieces of rough between the big pieces there will be many points of contact between the rocks of the load and the tumbling process will be faster and more effective.
This video shows you why filling your rock tumbler barrel between 1/2 and 2/3 full is essential.
If you don't have small pieces of rock to tumble you can add small ceramic media to the tumbler barrel. Ceramic media are used as small-size "filler" in tumbling. These tiny cylinders will also act like roller bearings in the barrel and make your load tumble with a lot more action - that extra action will increase the grinding rate in the barrel. See our video about selecting the right tumbling media.
We keep records of the rock we tumble. Even if your memory is better than ours this is a good idea. When you learn about something that works or something that doesn't you will have it recorded. This information can help you repeat great results and avoid bad ones. Also, we have trouble remembering which day a barrel of rocks was started. With a log we can be reminded with a glance. Print a copy of our free tumbling log and use it to keep your records.
When tumbling you will place enough rocks in the barrel to make it 1/2 to 2/3 full. Then add water up to just below the level of the rocks. And finally, add about two to three level tablespoons of grit for each pound of rock. Now seal the barrel and place it on the tumbler.
Here is some rock right out of STEP 1. Note how it is covered with a gray "mud". This mud is spent grit and tiny rock particles that were worn off of the rocks during tumbling. Wash the rocks thoroughly so none of this grit goes into the STEP 2 barrel. We wash our rocks in a colander over a plastic bucket so none of the mud goes down the drain.
Rock mud should never be washed down a household drain. It can clog your plumbing system. We wash over a plastic bucket to keep the mud out of the drain.
Be very clean! Before you replace the lid on your barrel, be sure that both the lid and the rim are perfectly clean. This will allow the lid to fit tightly and prevent leaks.
For burnishing we chop up a bar of Ivory Soap and add one tablespoon of soap slices for each pound of rock. See our video about burnishing polished stones.
Here's a few of our favorites! We hope you enjoy tumbling!
We highly recommend:
Modern Rock Tumbling by Steve Hart.
Learning is the fastest way to improve the quality of
rocks that you tumble. In this book you will learn from an expert with extensive
experience. You will increase your abilities, learn to save time, money and have a great reference book
that you will use again and again.