Vibra-lapping is the art of taking a rock with a flat face and polishing it. This is a very fun and rewarding aspect of the rock hounding hobby. However, it can be frustrating when things don’t go just right and you end up with a poor polish or worse yet a partial polish.
I use a 4 step process when I vibra-lap that works great. Here is how I do it...
1a. Make sure the rock is clean of loose debris. When I polish geodes I like to make sure they are scrubbed clean of all the clay or ash that might be on them. I do this before I cut them so I don’t end up with the crud in my saw. I have noticed a lot of people just put the rock in the saw and don’t clean it first. If little pieces do come off during any stage of the vibra-lappiong process remove them or they will get under the rocks and cause little squiggly lines in the rock that will make it so you have to start all over. This is tragic when you are in the polishing stage and discover them.
Make sure the cut-off burrs are gone. Often when you are finishing a cut there is a little burr on the rocks where it separates at the end. Don’t put these rocks into the vibra lap pans as it can damage the pan. I either grind them off or knock them off with a hammer.
1b. Charge the pan with 80 grit silicon carbide. The amount of grit to use depends on the size of pan you have. I use a 16" Covington lap and I charge it with a ½ cup of grit. Add enough water to make it a slurry and place the rocks on top of the grit and water. Make sure you add enough rocks to fill the pan 3/4 full. If you don’t use enough rocks you will "dish" the pan. Putting one rock in with the water and grit will act as a drill and cut into the pan. Because of the physics involved, the rock, grit, and water want to go to the center of the pan. If you don’t have enough rocks to fill the pan you will wear it down faster in the middle and it won’t be flat enough to do a good job. You can ruin a pan in about 2 hours of grinding.
1c. After 6 to 8 hours pick out a rock and scribble all over the face you are polishing with a pencil. Don’t use a marker! Place the rock back in the pan and let it go for 5 or so minutes. Remove the rock and rinse it with water. Don’t wipe it. If you can still see the pencil marks it is not ready for the next stage so place it back in the pan and add a couple of tablespoons of grit. If all the pencil marks are gone it is ready for the next stage. Now test all the rocks. Some rocks wear down faster than others.
1d. To get your rocks ready for the next stage you will have to wash them thoroughly!!! Once you have them washed, re-wash them and when you are done, wash them again. None of the grit can go into the next stage. Once the rocks are clean then you have to wash the pan or use a separate pan for the next girt.
If you have a different pan for each stage you will save yourself a great deal of time and effort in washing. Also by using a different pan you will cut down the chances of contaminating the next stage with grit from the last stage. I use a different pan for each stage, and it is amazing how much faster and more fun it makes the whole process.
2. Start the whole process over again with the second stage. I recommend 220 grit silicon carbide for 8 to 10 hours.
3. For the third stage I have tried several different options and have had the best success using 600 grit silicon carbide. 500 grit silicon carbide will work for about half the price but it may take a few hours longer.
4. Now for the polish stage. This is very critical. DO NOT LET ANY GRIT GET INTO THE POLISHING PAD!!!! Make sure your hands, rock, pan, and any covers you are using are free from all grit.
I recommend the felt pads as they are superior to any carpet or other types of pads in their results. The only polish to use is Tin Oxide. I have tried cerium oxide, and it works OK on some rocks. It doesn’t work on all rocks. Tin oxide works on all rocks and is faster and creates a better polish.
Tip 1. When you are not using the polish pan or pad keep it in a clean garbage bag to keep the dust and grit out of it.
Tip 2. If for some reason you need to leave the rocks for more than a day or so make sure they are soaking in water or it will take forever to get the grit off.
Tip 3. Tin oxide is next to impossible to get off if it dries on for more than a day or so. I just set the rock in a bucket of water and let them soak if I don’t have time to clean them right away.
Tip 4. I have found it very helpful to cover the vibra-lap with a cardboard box that is open on the front. This allows me to view the rock and air to circulate around the motor while containing the splashing. I "make" these boxes by using regular cardboard packing boxes, turning them upside down over the vibra-lap, then cutting one side completely away to allow enough air circulation.
Tip 5. Just about any rock will lap to a great polish. Some that don’t include sandstone, shale, clay stones or any rock that is very crumbly. You can seal these types of rocks with a sealant like Opticon (TM) or Hot Stuff (TM) and then polish them. It works very well.
Tip 6. Most vibra-laps are designed to hold up to about 35 pounds.
Tip 7. When you have a load of rocks going they tend to pound against each other. Sometimes when this is happening the edges of your rocks will get chipped. Obsidian and glass are really bad for this. I use old inner tubes and cut them up like really wide rubber bands and put them around the rocks. Placing a wooded dowel between them is another way of controlling the damage. But my favorite method and one that works really well is to wrap the rock with a layer or two of duct tape. You can peel it off between stages and add new tape to eliminate contamination.
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