Bench Tips

This page is intended for use by members only. Posts to this page are meant to aid members with making a quality product and are learned from our older, wiser members.

Ever have a nice piece of rock left over that cannot be clamped in the vise in the lapidary saw? I cut 2X4 studs into 2X4 squares (technically not 2″ by 4″ but you get the idea). You now have a 4X4 surface to glue a rock, and the wood can be clamped in the vise in the lapidary saw. Saw the rock into slabs, and there is no left over rock. Some people use Elmer’s glue, some use wood glue, but I prefer Gorilla glue for gluing the rock onto the wood.
Another tip to get more use out of the wood is to glue a rock on both sides of the piece of wood.

A CAB CAPTURE, By Nova Wells
It started because I was sick and tired of hunting through a dozen small boxes to find a special cabochon that I wanted to use in a pendant for a friend. The last straw was when I opened one box to find an obsidian cab broken from sliding back and forth in the box. I decided there had to be a better way.  I call the invention a “cab capture.” It is simply a double layer of matted fabric and heavy, clear plastic, stitched into squares.
I happened to have an old waterbed mattress pad on hand, but any heavy matted fabric, or a double layer of ordinary felt, will do. Having a matted fabric is important because when you cut it, it will not fray like a woven fabric will. Most knit fabric is not stiff enough for the job.  The top layer needs to be the very clear, heavy plastic sometimes used to cover windows or furniture. It is available at most fabric stores, as is felt in different weights.
First select the size of cabochon you want to capture. You will want different captures for large, medium and small stones. Then cut a sheet of matted fabric and a sheet of plastic the same size. There are no rules, but I find 9 x11 inches convenient. The finished product should fit easily in a drawer for storage.
Set the stitch length on your sewing machine for maximum length so you won’t end up with “tear along dotted line!” Use the selected cab to determine the size of squares or rectangles you plan to make and mark if necessary. Stitch the matted fabric and plastic together, making all the horizontal lines at one time and then all the vertical lines. Leave a tag of thread at the end of each line. My sewing machine does not like to feed the plastic through so I take care to grasp both ends of a beginning seam as it starts and pull gently so the stitches stay about 3/16th of an inch long and the layers stay together. Finally, stitch around the entire piece, going over the tag ends of the lines to keep them from raveling. Trim as necessary.
Now you are ready for the fun part. Gather a selection of cabs and a pair of sharp pointed embroidery scissors. On the matted side, cut a slit just barely big enough to slide a cab inside the pocket. Pull the edges together over the captured cab. Be sure to have the front of the cab facing the plastic. Turn the sheet over and admire your work. Now your cabs are safe from bumps, easy to see and easy to find.
When my daughter saw my collection of cab captures she said, “Since I’m inheriting these, please take a separate sheet of paper and identify each cab according to its square and be sure to number the captures and the identity sheets.” What a great idea! You could also add the value of each cab. Then years from now your family won’t sell all your cabochons for ten cents on the dollar because they will know what you’ve left them.
You’ll probably see two or three of our cab captures at the next show. Carl likes to use them to impress potential members and show visitors, who can safely pick them up without fear of breaking something.
Editor’s Note:
Perhaps address labels could be used to put on the back of each stone, OR on the face of the plastic where each stone is located. When the stone is used, removed the label from the plastic and place a new one for the stone that takes its place.

This article from: was the answer to my problem of not achieving that glassy finish on apache tears.  Once I purchased and used 1000 grit before using the cerium oxide my problem was solved.

(or any soft stone or glass…)

When you receive your obsidian rough, it is usually in chunks too large for tumbling, and because it doesn’t have cracks or fissures, it cannot be broken up effectively with a hammer and chisel. So just get rid of the chisel and go after it with a hammer. I always wear long sleeves, gloves, safety glasses, and a face screen or face shield to protect myself from the flying glass. These “flyers” which accompany the breaking process come out at supersonic speeds and can cut to the bone. Cover up everything you value before you even start.

As you break up the material, try to avoid using the slivers and thin pieces. They will disappear in a rotary tumbler, although you might try a few pieces in your vibratory tumbler. I prefer to select the fat “chunks” of obsidian so they can survive the tumbling process.

Note: If you are starting with “Apache Tears” (small round pieces of obsidian), you probably can skip the sizing process altogether.

Once you have enough sized material, rinse it and start loading your tumbler.

  1. Using a Rotary Tumbler

Loading a rotary barrel with obsidian is a little tricky. First put a cup or two of obsidian or Apache Tear pieces in a bowl, then an equal amount of ceramic shapes (forget the plastic pellets–ceramic shapes are the “high-tech” media to tumble obsidian). Mix everything in the bowl and pour enough of the 50/50 mix into the barrel so it is exactly ¾ full (3/4 of the way between the bottom of barrel and the bottom of the seated lid)–Little Red Store sells AccuFill Templates to make sure you get it to the same level every time (it’s important–see the other Technical Tip, “Making Perfect Slurries” for more information on properly filling a rotary barrel).

Now add the 80-Grit Silicon Carbide powder and finally, add water until it touches the bottom of the top layer of rocks. Stated another way, fill to about 3/8 inch below the top of the rocks. Fill the barrel the same way every time. Now put the top on the barrel, making sure that there is no grit on any mating parts which would cause it to leak. Immediately set the barrel on the rotating tumbler and leave it for a full week.

At the end of 7 days (168 hours) of uninterrupted tumbling, remove the barrel and pour the slurry and contents into a colander suspended over a bucket–blast the slurry contents with water until the rocks, shapes and barrel are cleaned of all slurry.

Inspect your rocks–they will probably need at least 3 weeks in the 80-grit to get them nice & rounded, if you started with sharp obsidian. However, if you started with rounded Apache Tears, a week or two in Stage 1 is all that is required.

Now refill your barrel with the clean washed rocks–add more ceramic shapes to bring the level to the ¾ point–then the appropriate grit–then water–finally the lid, as before, and fire it up for another week.

When the rocks are sufficiently rounded, look at the 80-grit scratches in them with a 10-power magnifier so you know what they look like. Now proceed to Stage 2 (220-grit) for a week, and clean up as before. Now look at the rocks with the magnifier again–if you still see the 80-grit scratches, proceed for another week in Stage 2. If you see only smaller (220-grit) scratches, you can move on to Stage 3 (600-grit).

After a week in Stage 3, use your magnifier to view the scratch pattern again–if you still see the 220-grit scratches, plan to spend another week in Stage 3. If the only scratches you see are Stage 3 scratches, proceed to Stage 4 (1000-grit) for a week–then follow this same inspection procedure. When all you see are Stage 4 scratches, it’s time to proceed to the polish stage. Wash up really well, load the barrel properly, and run the load for 1 to 2 weeks in Cerium Oxide polish. You can tell you are done polishing when a dried rock looks just as shiny as a wet rock. Another method is to take a cleaned piece of obsidian from the batch and rub it vigorously on a Polish Stick which has been moistened and sprinkled with Cerium Oxide polish. When the un-rubbed portion of the obsidian looks as good as the rubbed portion, you have obtained the very best polish you can from the rock.

In summary, you let the rocks tell you when it is time to move from one stage to the next–by observing the scratch patterns in the rocks. Being human beings, most of us want to move on to the next stage before they are really ready. We have to resist this urge to move on too soon!

Here’s a brief summary of the soft stone (and glass) rotary tumbling process:

Stage 1 (80-Grit)                 To round edges & remove sharp corners
Stage 2 (220-grit)                To remove Stage 1 scratches
Stage 3 (600-grit)                To remove Stage 2 scratches
Stage 4 (1000-grit)             To remove Stage 3 scratches
Stage 5 (Cerium Oxide)      To remove Stage 4 scratches and achieve a high polish.

When someone calls the Little Red Store to tell me they can’t achieve a high polish on a rock known to take a high polish, I ask the following questions to help find the problem:

  1. How many weeks did you spend in each stage? (This is an indication of overall operating procedures)
  2. Did you load properly–3/4 full every time? (Indicates the efficiency of the tumbling process)
  3. What did your “spent” slurries look like? (Similar to #2–helps identify how efficiently the rocks were tumbled)
  4. How did you determine when to go to the next stage–did you look at the scratch pattern after every wash-up or did you “guess”? (Most people guess…)
  5. Is it possible that your powders are contaminated? (Very common problem–wastes their time)
  6. Is it possible that small holes in the rocks carried grit into the following stage? (Another common problem which causes no end of frustration)
  7. What color is your Cerium Oxide polish? (If it’s not pink, they do not know what they are using)