Rock Tumbling 101

This is the most comprehensive list of instructional steps to polish rocks that I have yet to find. (Notes in italics I have added))

TUMBLING
PROCEDURES

PREPARATION
1. Wash the stones thoroughly. Be sure there is no debris attached to the stones. Use a brush and soapy water if necessary. (This is the time to inspect the rocks, and I'll split those that have large cracks or inclusions. You could use a 'dremel' to clean up any large pits and remove offensive or unnatural shapes, and do a little preforming. As for cleaning, I don't do much other than a quick rinse, I figure the 60.90 grit is the intial stage for getting the corners rounded and edges smoothed, and a little debris will just br worn down by the Silicon Carbide, or, if it is hard, it will aid in the shaping of the stones.)
I use a sledge hammer and a chisel to break the rough down to tumbling size. A railroad tie on it's side in a box gives me a hard surface to pound on, and keeps chips from flying. Then I go back through the stones and knock off any offensive edges, split vugs open and seperate any noticable inclusions or cracks that would never wear down in the grit. I may use a Dremel with a diamond wheel to give the 60/90 an assist on some of the more objectionable edges. This is sort of 'preforming', when I help determine the shape.
.2.Sort your stones by size and hardness into groups or batches. Soft stones will grind away before hard stones are ready for the next step. Stones of nearly the same size will have more points of contact and therefore will produce a more thorough and faster grinding action. If certain shapes or sizes are desired, you may want to preform your stones by grinding them on a lap, grinder or Dremel first. (If you mix your softer stones with your harder stones in the 60/90 grit, just be sure to check on them after 2 or 3 days to get an idea how fast the softer ones are wearing. {I had some Angelite in with Agates one time and after 7 days, they were gone.} I will run a mix like this and after one week pull out the softer stones that are shaped and recharge with grit and water and continue to run a week or more. I might even add some more stones after that first week and again check after 7 days and pull out what is done, and so on. This is easy to do if you have a tumbler barrel for each grit size, but if you have one barrel it's a bit harder to do, because my 60.90 barrel is never empty and it never stops running.)

COARSE GRIND
3. The amount of stones put in a tumbler barrel depends on the size of the barrel and the stones themselves. The best tumbling action occurs when the barrel is filled 50% to 60% of its capacity. Fill the barrel with your stones to 1/2" above the half-way mark. Remove the stones and weight them. This weight will help you to determine how much grit is needed. Record this weight for future reference. Use the following ratio to determine the amount of silicon carbide grit needed for your batch:

One pound of grit per eight to ten pounds of rock.

Put your batch of rocks back into the barrel and add grit accordingly. If the rocks are chips or have rough crude surfaces, start with a coarse grit (60/90 mesh). If the rocks are water worn from tumbling in stream beds or already tumbled by ocean waves, start with a medium grit (120/220).
Get these little plastic measuring cups from hospitals, the drugstore, or Nyquil.They are 1 ounce, which is 2 tablespoons. Put one in your 60/90, one in your 120/220, 500, 1000 and one for each polish. This keeps you from contamination.

With a 3# barrel I just put 2 of these measuring scoops in with the rocks, that is 4 tablespoons.

Simple and good enough for me. I have found that this is really close enough and I usually have no grit laying in the bottom of the barrel at the end of the cycle.
4. Add water into the barrel so it is either just touching the bottom or the middle of the top layer of rocks. Put the cover on and secure it. Place the barrel into position on the tumbler.
Left is a barrel of Rocks...Duh!... with the water added, and you can't see the level. But...

Right is a jar of Rocks, with a line drawn on the level that I fill my tumblers up to with water.

Then add grit and pellets.
5. Put the tumbler into operation and observe its action for a few minutes. Check for loose or slipping belts or pulleys. Listen to the sounds coming from within the barrel. Is there sufficient amount of action taking place? If there isn't, shut down the operation, open the barrel and inspect the consistency of the mixture. If the mixture is too dry, add a little water. Put the cover back on and continue as before. If everything appears to be functioning properly, you can leave and come back periodically to check the operation.
6. It will take an average of four to six days of coarse grinding. Sharp-edged or broken pieces of agate may require as much as 1 month of coarse grind operation. After each 24 hours of operation, shut down the operation. Remove some stones from the barrel and examine them. You can add or decrease the grinding time according to how much more rough grinding you want performed. If you want to continue with the coarse grit, inspect the grit and the consistency of the mixture. If the grit no longer has sharp edges, you may want to add more coarse grit. (I always dump the barrel, rinse the stones and add new grit and water) If the mixture is too dry, you may want to add a little more water. Place the stones back into the container, seal the barrel, place it into position, and start up the operation. Observe and listen to see if the operation is functioning properly. You can leave and check back periodically. When the coarse grinding phase is finished to your satisfaction, you can proceed to the next step. If a few stones need more coarse grinding, you can remove them from this batch and re-tumble them later in another batch.
7. Remove all of the material and stones from the barrel and place in a pan. DO NOT use an aluminum pan. It may discolor your stones. Plastic is preferred. DO NOT wash the waste material down your drains. It may harden in the traps or pipes and require major plumbing repairs to clear the pipes. Clean the stones, the barrel, the lid, the pan and any other part that has made contact with the grit mixture. Wash everything and your hands thoroughly. You do not want any previous grit particle left to contaminate the next mixture. It may produce scratches.

MEDIUM GRIND
8. Place the stones back into the barrel. If they do not fill the barrel to the half-way mark, you may need some filler material. The filler material is available from lapidary supply stores. Inexpensive marbles, plastic pellets, or crushed walnut shells make good substitutes. Add the filler material until the half-way mark is reached. (You may add about one tablespoonful of baking soda, I do not). Add 220 or "240 & finer" grit to the mixture in the same quantity as the coarse grit. Add water into the barrel so it is either just touching the bottom of the top layer of rocks or until it comes up one 1/16 of an inch on the top most layer (do not ever cover the stones comepletely with water, that is too much). Put the cover on and secure it. Place the barrel into position on the tumbler.
9. Put the tumbler into operation and observe its action for a few minutes. Check for loose or slipping belts or pulleys. Listen to the sounds coming from within the barrel. Is there sufficient amount of action taking place? If there isn't, shut down the operation, open the barrel and inspect the consistency of the mixture. If the mixture is too dry, add a little water. Put the cover back on and continue as before. If everything appears to be functioning properly, you can leave and come back periodically to check the operation.
10. It will take an average of about four days, or 96 to 100 hours. After each 24 hours of operation, shut down the operation. Remove some stones from the barrel and examine them. You can add or decrease the grinding time according to how much more grinding you want performed. If you want to continue, inspect the grit and the consistency of the mixture. If the grit no longer has sharp edges, you may want to add more grit. If the mixture is too dry, you may want to add a little more water. Place the stones back into the container, seal the barrel, place it into position, and start up the operation. Observe and listen to see if the operation is functioning properly. You can leave and check back periodically. When this grinding phase is finished to your satisfaction, you can proceed to the next step. If a few stones need more grinding, you can remove them from this batch and re-tumble them later in another batch.
11. Remove all of the material and stones from the barrel and repeat the cleaning procedures used after the coarse grit operation. Clean the stones, the barrel, the lid, the pan and any other part that has made contact with the grit mixture. Wash everything and your hands thoroughly. You do not want any previous grit particle left to contaminate the next mixture. It may produce scratches. This is why multiple barrels is so much easier, as you do not have to be so meticulous in your cleaning.

FINE GRIND
12. Extreme care should be taken from this point on to prevent the stones from chipping or breaking. Place some water in the barrel first and then place the stones gently into the barrel. If they do not fill the barrel to the half-way mark, you may need some filler material. Don't use contaminated filler material from previous operation. Add the filler material until the half-way mark is achieved. Add about one tablespoonful of baking soda. Add 500, 600, or "600 & finer" grit to the mixture in the same quantity as the coarse grit. Add water into the barrel so it is either just touching the bottom of the top layer of rocks or until it covers the rock by no more than 1/16 of an inch. Put the cover on and secure it. Place the barrel into position on the tumbler.
13. Put the tumbler into operation and observe its action for a few minutes. Check for loose or slipping belts or pulleys. Listen to the sounds coming from within the barrel. If there isn't sufficient action taking place, shut down the operation, open the barrel and inspect the consistency of the mixture. If the mixture is too dry, add a little water. Put the cover back on and continue as before. If everything appears to be functioning properly, you can leave and come back periodically to check the operation.
14. It will take about 72 to 150 hours for the stones to be ready for the polish phase. After each 24 hours of operation, shut down the operation. Remove some stones from the barrel and examine them. You can add or decrease the grinding time according to how much more grinding you want performed. If you want to continue, inspect the consistency of the mixture. If the mixture is too dry, you may want to add a little more water. DO NOT add more grit. Place the stones back into the container, seal the barrel, place it into position, and start up the operation. Observe and listen to see if the operation is functioning properly. You can leave and check back periodically. When this grinding phase is finished to your satisfaction, you can proceed to the next step.
15. Continue to take extreme care not to damage the stones. Remove all of the material and stones from the barrel and repeat the cleaning procedures used after the coarse grit operation. Clean the stones, the barrel, the lid, the pan, the sink faucets, etc. Wash everything and your hands thoroughly. You do not want any previous grit particle left to contaminate the next mixture. It may produce scratches.

POLISH
16. Allow the stones to dry and then examine them very carefully. Remove any stone that is chipped, broken, or has very sharp edges. The damaged stones will scratch the rest of the batch if left to remain. Place the stones gently into the barrel. If they do not fill the barrel to the half-way mark, you may need some filler material. Filler materials such as sawdust, wood shavings, cornmeal, walnut shells, and rubber strips (cut-up rubber bands) are ideal. I still prefer pellets. They will help prevent damage to the stones by absorbing some of the tumbling (banging) action. Add the filler material until the half-way mark is achieved. Add about one teaspoon of detergent soap. I do not add soap at this point. The best type to use, is a "sterile" form such as Ivory Snow powder, as most other detergents have additives such as chlorine which could chemically react with the stones as they are being polished. Using a pure soap is better. Add cerium or tin oxide to the mixture in half the quantity as the coarse grit. Add water into the barrel so it is either just touching the bottom of the top layer of rocks or until it covers the rock by no more than 1/16 of an inch. Put the cover on and secure it. Place the barrel into position on the tumbler.
17. If it's possible with your unit, reduce the speed of rotation by about twenty percent. Put the tumbler into operation and observe its action for a few minutes. Check for loose or slipping belts or pulleys. Listen to the sounds coming from within the barrel. If there isn't sufficient action taking place, shut down the operation, open the barrel and inspect the consistency of the mixture. If the mixture is too dry, add a little water. Put the cover back on and continue as before. If everything appears to be functioning properly, you can leave and come back periodically to check the operation.
18. It will take about 48 to 150 hours for the stones to be completely polished. After each 24 hours of operation, shut down the operation. Remove some stones from the barrel, wash and examine them. If they become duller as they dry, then they are not completely polished. Carefully put them back into the barrel and polish them for another 24 hours. Inspect the consistency of the mixture. If the mixture is too dry, you may want to add a little more water. Seal the barrel, place it into position, and start up the operation. Observe and listen to see if the operation is functioning properly. You can leave and check back periodically.

FINAL CLEAN-UP
19. When you are satisfied with the polish results, Remove all of the material and the stones from the barrel and repeat the cleaning procedures used after the coarse grit operation. Clean the stones, the barrel, the lid, the pan, the sink faucets, etc. Wash everything and your hands thoroughly. Carefully place the stones back into the barrel. Add enough detergent soap powder and water to make a thick soapy solution. Tumble the stones for 6 to 12 hours. I use a mix of 1 Tablespoon of Borax and 1/2 Tablespoon of Cascade powder for 1 hour so they don't bang around so long risking additional fracturing and my results have been excellent. Remove the stones from the barrel carefully and place them in a plastic colander. Wash them thoroughly. Spread them on a cloth or towel to dry. A blow dryer works perfect. Those that are properly polished will have the same appearance as when they were wet. If some stones are not satisfactory, you can re-run them later with another batch as fillers.

TID-BITS
You may want to add fine granular sugar or sugar paste/slurry to your pre-polish and polish stages. Sugar makes the slurry very thick. This cushions the rocks as they tumble. Add twice as much sugar as pre-polish/polish to make the polishing slurry thick but not dry.

The actual amount of grit and polish depends on what you are wanting to shape and polish, size and amount. Vibratory tumblers use less grit and polish than rotary type. Normally, rotary tumblers use an 8:1 to 10:1 ratio of rock to grit and 16:1 to 20:1 ratio of rock to polishing powder. The idea is to use the least amount that would provide the most effective use giving the best results. Experiment and keep records.

There are "Media Kits" designed for deburing and finishing metal castings and stampings in vibratory tumblers. First two steps of the kits process uses plastic media embedded with silicon abrasive of different mesh grit, while the last step utilizes a dry polish. This process deburs and produces a high luster on a number of metals without problems of impact damage.

Always take notes. Record your procedures, any changes made, the time you start and stop an operation, and how long each operation takes for the type of material you are tumbling. Don't be afraid to experiment.