Rock Specs

If you have information you would like to contribute to any of these rock spec pages – Only Oregon, Gems & Minerals, Paleo Room or Ask Rocky, please contact us.


[click here to download [WAMS Thunderegg Brochure]

In 1965 the Oregon legislature designated the Thunderegg as the official state rock. However, the Thunderegg has been a very important treasure to Oregonians for much longer.The Thunderegg has been highly prized by collectors, lapidarists, jewelry makers, and interior decorators for nearly 100 years. Since the mid-1930’s, thousands of visitors from every state and many overseas companies have visited Oregon to hunt Thundereggs. These highly prized stones are made into beautiful jewelry, pendants, pen stands, and bookends.

Hart Mountain, OR picture jasper cabochon.

Tips, Tricks, Hints and Notes:

Tips and Tricks are from previous issues of Rockhound Rumblings. To search for a topic – go to your Internet Browser’s Main Menu > Edit > Find and enter the subject you are looking for.

Sanding Turquoise
from Lapidary Journal – 10/01
Some turquoise has a tendency to glaze over during sanding. To prevent this, place your turquoise cabs in a shallow dish of water for a while before sanding, then use more water when sanding. Keep it very cool.

Defining a Cabochon
from Lapidary Journal – 9/01
The definition of cabochon has changed since I cut my first one over 50 years ago. At that time, a cab had to have a flat bottom, a domed top, and a round or oval outline. Variations were few. Certain sizes were more acceptable than others, and specific dome heights were preferred. Beveled bottoms were important. The first cut stones that might have stretched the cabochon category were hearts. Then my husband made me an agate cross with a slightly curved top, which could also qualify as a cabochon today. But the first articles I remember which really started early lapidaries thinking cabochon rules weren’t “set in stone” were in Lapidary Journal in the early 1960s. “Cabochonets” by Tom Hubbard (April ‘63) combined freeform shapes with cabbing and “faux facets” forerunners of today’s imaginative stones. “Expanding the Cabochon” by Merill Murphy (Jan ‘64) showed dozens of elegant and graceful shapes often using the stone patterns as guides. Not all cabs today have domed tops, and all don’t even have flat bottoms.

Just what are cabs today? They are polished gemstones usually intended for jewelry and mountings, but they are not faceted. Add whatever you wish to that definition.

How to Work Amber
by Frank Monahan (Puget Sounder – 8/01, Rock Rollers – 10/99, Delvings – 8/98)

  1. Use wet/dry sandpaper. Always sand amber wet. Start with 100 grit, take off all outer coating.
  2. Dip in water, then hold against strong light to locate insects.
  3. Shape and/or round corners with metal file.
  4. Using 200 grit sandpaper, sand until all deep scratches from 100 grit are gone.
  5. Finish sanding with 600 grit. Use circular motion to prevent long scratches.
  6. Let piece dry. Examine your finish carefully to see if you missed any bad spots. Remove bad spots before proceeding.
  7. Put regular toothpaste on wet wash cloth. Make a paste and rub amber to polish. (Gel type toothpaste isn’t abrasive enough).

Desert Survival
Submitted by George Goetzelman –
The will to live is the secret of Desert Survival. Keeping calm, along with common sense are the ingredients of the will to survive in the desert. For many years, lives could have been saved by merely following a few tried and tested rules.

In case you are lost or stranded, generally it is best to stay where you are or with your vehicle. If you decide to move, make sure which is the right move and then make it with a positive plan. A lot of rescued people will tell you “I was going to do just that”. When out in the field, compare land marks. Watch for distinguishing peaks or rises, buttes and rock formations. Your compass is an invaluable tool. It is one of the most talked about tools for survival but the most under-rated by the individual. A compass at home does you no good when lost in the desert. Learn to use it and – USE IT.

Fact: Lost persons tend to walk in circles. Most survival writers claim this is deadly. This writer contends this is an inborn instinct and may be a factor in a lot of lost persons being rescued. While walking in circles, this factor may be just the needed time a rescue party needs to catch up with a possible victim of the desert. Actually instinct is trying to find its way back to a known landmark.

Food For Thought: In case you think you are lost, go a little further on this circle finding bit. Now, widen the circle from a given point – don’t lose your given point. In this way, you may come across a landmark, path, or even the road you came on. Unless you know your direction, don’t wander aimlessly. Proceed with a plan in mind. To my knowledge, this is only theory but is worth thinking about.

While climbing to Picacho Peak in Southern California I stopped and looked around and reUntitled 11alized “I’m lost”. I circled around the peak and quickly located my bearings. I realized this method worked for me. I believe I would have eventually found my way, but had saved a lot of aimless hours of hiking.

Qualifications for Being a Rockhound
(via Hatrockhound Gazette, 8/01, Clackamette Gem, 6/01)

  1. Love of the outdoors – where else can you find rock.
  2. Strong Back or Good Judgement – rocks gain weight with every step.
  3. Sense of Humor – being able to appreciate someone else’s find after you just stepped over it.
  4. Cheerful – smile even if every muscle and bone in your body aches.
  5. Adventurous – daring to take a road, even it it looks like it goes straight up.
  6. Persistent – not satisfied until you have turned over every rock twice.
  7. Determination – visualizing a beautiful gem cut out of a plain rock.

Gold Leaf (Golden Spike News – 6/01 via SCFMS Newsletters & Del Air Bulletin)
Is gold leaf made of solid gold? Yes! A gold block is pounded into a thin sheet by machine. Then, it is reduced to transparent thinness by hand. It can be beat so than that 1200 sheets of gold leaf are thinner than a sheet of writing paper.

Biggs Jasper (Golden Spike News – 6/01 via Rock Rattler & Glacial Drifter)
Biggs jasper is one of the more recently discovered picture rock materials. The first piece was found about 1960 in a creek bottom south of Biggs Junction, Or. It is one of the more distinctive jaspers even though it lacks brilliant colors, its design is unique among siliceous rocks. It takes an excellent polish.

Biggs jasper seems to have developed from the muds of short-lived streams that evolved on the surface of a cooled basalt terrain. The raw materials (plastic colloids, silica, clay and iron came from the weathering of recent igneous rocks and were deposited in the settling basins of stream channels. Heat and pressure from volcanic activity that served to form jasper, small creeping motions led to the marbled rosettes and picture designs.

Biggs jasper is sandwiched between two basalt lava flows that cover Oregon, Washington and parts of Idaho. That plants and animals inhabited the newly formed water courses is shown by the fossil fish found in the area.

White Buffalo Turquoise
(Rock Rollers-5/01, via Rockhound Gazette-12/00, Glacial Drifter-4/01)
When discovered in the Dry Creek Mine on the Shoshone Indian Reservation near Battle Mountain in 1993, the [the discoverers] were not sure what it was. Because of it’s hardness, it was decided to send it to have is assayed. Their suspicions proved correct. It was, in fact, white turquoise. It was not until 1996 that it was finally made into jewelry.

The Shoshone Indians are not known for jewelry work and as a consequence they sell or trade it to the Navajo in Arizona who then work it into jewelry. Because white turquoise is as rare as a white buffalo, the Indians call it “White Buffalo” turquoise.
Turquoise gets it’s color from the heavy metals in the ground where it forms. Blue turquoise forms when there is copper present, which is the case with most Arizona turquoise. Green turquoise forms where iron is present, as with most Nevada turquoise. White turquoise forms where there are no heavy metals present, which turns out to be a very rare occurrence. To date, no other vein of white turquoise has been discovered anywhere else. When this current vein runs out, that will be the last of it.

Lapidary Polishing Compounds (Golden Spike News, 4/01)
For economy dedicate a buff, lap pan to a particular polish and simply recharge with fresh polish as required to maintain effectiveness.

Cerium Oxide – the best gemstone polishing compound for most uses. Best with opal, agate, quartz, obsidian. Not as effective with soft material or stones that tend to undercut.

Micron Alumina – a 5 micron polishing powder developed for computer disks. It is the best polish for seashells, pretty good for soft stones and excellent as a pre-polish in vibratory tumblers and laps – not rotary tumblers.

Aluminum Oxide, MAP – preferred by many to Linde A, this is a slightly faster and more economical rare earth polish that we call Miracle Atomic Polish.

Tin Oxide – a long time favorite. Use on leather for polishing turquoise and all soft stones.

Zirconium Oxide – a rare earth polish that is especially good for tumblers and laps. The most economical effective polishing media. White and will not discolor gemstones.

Linde “A” – A tremendous favorite with gem cutters whether faceting or polishing cabs. Relatively expensive, you should consider polishing the stone then giving it a quick hit with Linde A to attain a super polish. Available as powder to mix with water or an emulsified cream with the consistency of hand lotion that does not separate in solution

Oxalic Acid – used for polishing carbonate type onyx when mixed with another polish such as Tin Oxide. In a strong solution with water, it is used to clean iron stains from specimens, i.e. Quartz. Mix with hot tap water by stirring in oxalic crystals until the water is saturated and will not dissolve any more. Crystals forming along the sides of the container indicate a saturated solution and should they disappear, you need to add more. WARNING: While this is a relatively mild acid all precautions must be taken to keep it out of eye, mouth, etc.

Some Common Uses of Fluorescence
(Rock Rollers, 3/01, excerpt article by Emily Adams, CFMS Newsletter 9/98)
Gemology – separate synthetic spinel which fluoresces from aquamarine which doesn’t.
Criminology – dust for fingerprints, mark ransom money.
Mining – locate uranium minerals, zircon ore, diamond and ruby.
Detergent – make bleaches with fluorescent materials to produce “whiter” results.
Postal Service – detect invisible alterations in counterfeits, special coding for sorting.

Whoa! Don’t Buy That Shiny Gem
(via Golden Spike News-5/01, Chips-12/00, Rock Rollers-11/00)
Technology has given new meaning to the old phrase “hot gem”. As you know irradiation can darken a crystal producing a deeper color. Deep, vibrant colored gems also sell for top dollar. Now what’s supposed to happen is the gem is radiated then stored in a lead container for several years until the radiation has dropped to safe levels. More time means more overhead. Unfortunately, some traders care more about reduced overhead than morals and have released HOT cat’s-eye gems to the market. Some of these were measured at 51 times the US radiation limit. Buyer Beware! If you’re not careful, more than your watch will glow in the dark.

Wrapping Specimens (via Rock Chip Reporter – 2/01)
Use old phonebooks for wrapping your small specimens. It can be kept in your trunk so the pages can be torn out as needed.

Patching Soft Stones
Excerpted from The Rollin’ Rock March 2001 via several others
Some soft stones such as malachite, azurite, etc. can be patched to fill small pits and cracks. Take a scrap of material to be patched, crush it and mix with epoxy. Clean the stone thoroughly with alcohol, warm and coat the pits with epoxy. Then fill the pit with the mixture of epoxy and powdered stone. Work it well with a toothpick or pin, leaving it a little above the surface of the stone. Let it cure completely, sand well and polish, using care not to get the stone hot.

Another One on Jade (Golden Spike News 3/01, Emerald Gems 2/01
The more milky the water is when cutting jade, the better the grade of jade. If the water isn’t milky, then you don’t have true jade, you have something else.

Good Looking Specimens (Owyhee Gem 2/01, Rock Rollers 10/00)
Endust will help a fossil for a display look clean and detailed. It gets rid of the dusty look. It is also great for bringing out the colors of a prize agate that the owner hates to cut and polish.

Polishing Hint (Rock Licker – 3/98, Rockpile – 4/97, Rocky Reader -2/97)
One reason for polishing a stone all over – front, back and edges – is that the polishing acts as a sealer. It seals and keeps the water in opal; it prevents natural corrosion and helps stop the absorption of harmful substances such as perspiration.

Worn Vise Jaws (Owyhee Gem – 8/98, via Rock Rollers 5/97)
If the wooden jaws of your slab saw vise are chewed up and need replacement, use second growth hickory instead of hard maple. It will grip the stone just as tight and will last much longer.

Storing Polish Compounds
(Owyhee Gem – 1/98, Rock Rollers – 4/98, The Tumbler – 1/98)
Use glass jars to store your buffing compounds. Coffee or tin cans can rust under the wet coumpound and the pieces of rust can scratch your specimens.

Soften the Blow (Owyhee Gem – 10/98, Rock-a-teer – 6/97)
To break a cavity filled with fragile crystals from the large matrix specimen – fill the cavity with fine dirt and hold the piece with the cavity facing up to retain the dirt while you trim the specimen. The dirt prevents the shock of the hammer blow from loosening the crystals.

Pre-Polish (Rock Licker – 3/98, rock Buster News – 5/97 , via Mtn Gem)
The use of pre-polish in tumbling is almost a must. At the very least, use a soap run prior to going into polish. This is a flushing action and will losses up any grit that you were not able to wash out from your grinding runs.

False Fossil Oddities – Dendrites
(via the Rock Licker-3/98, & Pick and Pack-10/97)
Perhaps the most common geologic oddity is the dendrite, which resembles a tiny fern frond or colony of algae. The term “dendrite” refers to a branching figure resembling a fern frond, branch or tree. They are usually formed in thin, hard-bedded shales and limestones. Concentrations of the manganese mineral called pyrolucite (black manganese dioxide) percolates into the cracks and fissures of shale and limestone, leaving behind a residue forming the dendritic pattern.

The terms “hardness” and “toughness” are sometimes confused when comparing the qualities of gemstones, and there is a great deal of difference. Diamond is by far the hardest of gemstones, for it will scratch, cut or polish any other stone. But, for toughness (resistance to chipping and breaking), jade has diamond beat. A diamond will easily cut or scratch jade, but a jade hammer can in turn crush a diamond to powder. It is the crossmatted structure of jade that makes it nearly impossibly to break. If you drop a solid jade cabochon on cement and it breaks, better check, it probably wasn’t jade. The Chinese used jade for anvils, just as we use steel, and sometimes the same anvil was used for generations. Jade for axes and hammer-line tools, centuries ago, was a practical, useful and highly values material.

Great Cleaning Tips (via Golden Spike News-7/98, and Lapidary Journal)

  • Remove algae and lichen from rocks by soaking them in ammonia water followed by the use of a stiff brush.
  • To remove cutting oil from slabs, first place them in kitty litter to absorb the oil, then put them in warm water with a dishwashing detergent.
  • Wash fluorite specimens only in cold water.
  • Remove the sludge from saw coolant by filtering the coolant through large brown paper bags. Because there will be a loss of volume you must add new oil.

Advise on Opals (via Golden Spike News-7/98, and Lapidary Journal)
The newest advise on opal is that you should not store rough opal in water or glycerine. Most opal is found in desert environment and does not have to be kept moist. A well-polished opal will hold up well without the frequent baths that are sometimes recommended. NEVER put opal in an ultrasonic cleaner.

Vinegar – not just for salads
(From Rocket City Rocks & Gems-6/99, Stone Age News-9/00)

One way to remove carbonates such as calcite from quartz and amethyst is to cover the specimen with fresh vinegar and allow to stand overnight. Repeat if necessary. Wash and then place crystals in washing type ammonia for 8-1/2 hours. Remove, rinse thoroughly, wipe and air dry.

For the gloss finish on tiger-eye, polish once, dry the stone, then put a drop of vinegar on it. Let stand for a few minutes, then give it a second polish.
Mother-of-pearl for inlay work can be softened by soaking in white vinegar. It then can be easily cut.

If you have sore hands from hard rock mining, soak your hands in warm vinegar water and the swelling and soreness will disappear.

Dark household vinegar will dissolve epoxy glue by soaking overnight.

Heard around the faceting table: spray vinegar on your lap while polishing with water – or mix 50/50 water & vinegar in your water cup. This lowers the ph, giving a faster and better shine.

Polishing Cabachons
(From Jasper Jargon 1/00, Polished Slab 5/00, Golden Spike News 6/00, Clackamette Gem 10/00)
It is better to polish the stones at a slower speed. If you don’t have a speed control on your polisher, just work the stone on the center of the disc. What you are concerned about is the surface speed. Remember that your disc surface is one complete revolution at two inches from the center will travel 1.26 inches and at eight inches from the center, it will travel 25.12 inches. You should use the area near the center for polishing stones slower and the outer edge for polishing stones faster.

Polishing Curved Surfaces
Submitted by Rudy Appleby, WAMS
To polish small curved surfaces in carving with your flexible shaft tool, visit your auto supply store and purchase a real leather chamois (or use any reasonably thin, clean, uncontaminated leather you have around).

Select a felt, rubber or resin tip on a mandrel and lay the tip on the leather and cut enough leather to cover the tip up to the shank of the mandrel plus about 1/2”. Wrap the tip tightly, gathering the overlap uniformly at the shank. Secure the leather with a tie. I use a rubber band, pulling and looping it over the tip, pull it out and loop over the tip repeatedly until tight. Trim off the excess leather above the secured point on the shank as desired.

You now have a leather “micro” polisher. Dip the tip in water to get it wet, then dip in optical grade cerium oxide (or whatever you prefer). Set the tool on low speed and polish as you would on the “big buff” (keep it damp and loaded).

For safety purposes: safety glasses always; make sure the leather is securely fastened at the shank by checking to see if you can pull it off in between charges of polish; and check to make sure you aren’t “burning” through the leather (this won’t help the polish).

Helpful Hint From NWF 8/00 Newsletter
(via Owyhee Gem&Yakima Gem & Mineral News, 2/00)
Rubber should not come in contact with silver. Never put a rubber band around any silver or you will get a permanent stain.

Spencer Opal
(From Emerald Gem 9/88 – Excerpts from article by Warren Neer, EMC)
Spencer opals are usually seen in triplets, made up of three parts glued together with a clear epoxy. The base is usually basalt rock, the center a very thin layer of precious spencer opal ground perfectly flat, and the top layer is optical grade quartz glued. It is then ground to desired shape, sanded, and polished.

Spencer opal comes from a mine close to Spencer, Idaho. Types of fire include pinfire, harlequin and broad flash. Pinfire has small points of fire the size of a pin head or smaller. Harlequis is the size of a match head, and broad flash has large splotches of color. Fire colors come in red, orange, gold, yellow, blue, green, fushia, purple, and combinations.

When looking at Spencer opals to purchase, look for flaws, type of color (fire), the color play in various types of light, the finish, look for pits, scratches, or sanding marks in the quartz cap.

Tips on Selecting Good Material
submitted by Mike Gaines
At a recent meeting I was asked, “How do I know I’m buying good quality material?” This is a hard question to answer, but here are a few tips that may help:

  1. Look for certain characteristics in any piece you buy:
    • Hardness – the harder the material, the better polish you’ll achieve
    • Flaws or Fractures – will the piece stay together or will it break in the saw? Can you easily work around the flaw?. If it’s really rare, you might want to take a chance. Many plumes are pitted on the surface, but you can learn to fill those flaws with epoxy. If you’re buying a chunk, does it look like the part you wish to cab goes deep enough or is it only on the surface?
    • Thickness – A lot of great slabs are unworkable because they were cut too thin. Slabs cut too thick are extremely hard to recut and may end up too thick for many jewelry mounts. 1/4 inch or there abouts, is a good cabbing slice.
    • Color – is it natural or dyed? Ask the dealer, they usually can tell you.
    • Pattern – Is the pattern too perfect? It might be reconstituted (they take scraps of the original rock and under high pressure glue them together, adding artificial patterning). While reconstituting is not bad, you should know that you are buying something that is not in its “natural” state.
    • Special Features – Plumes — are the plumes so dense that they’re hard to see? Plumes in clear agate make the best stones.
    • Banding – are the bands wide enough to show the pattern clearly? Rutile – Like plumes, rutile shows best in clear agate, too much rutile won’t show as well. Crystal pocket – many people consider this a flaw–depending upon how you orient the pocket, it can actually make a spectacular piece. Carry a small template so that you can “window” a piece before you buy.
    • Matrix – Sometimes you find a really great piece, but there’s a lot of unusable matrix attached to it. Ask the seller if they took into account the matrix in determining the price. Depending on how bad you want the piece, you might get them to reduce the price. It usually doesn’t hurt to ask.
  2. Buy a small amount of the best material, rather than a lot of the cheap material. I can’t emphasis this enough. Getting a “bargain” isn’t really a bargain if when you get home, you spend a lot of time and energy creating a piece that is only so-so, and you have a lot of waste to get rid of.
  3. When you find nice material for a reasonable price, buy extra. Many times I’ve kicked myself for not buying more and never saw the material for sale again. You can always use the extra for trading material or offer the excess to a rockhound friend for a reasonable price and recoup part of your investment.
  4. Get acquainted with the Dealers. If they know what you like to work on, they can keep their eyes open for the material and steer some great material your way before it goes “out on the table”. Learn to pick up business cards from dealers you like to do business with—make notes on the back of the card regarding what they offer. (Stationary stores have clear binders designed just for holding business cards and believe me, they work great to keep with the telephone book.
  5. Last, and probably most important—ask friends and fellow rockhounds for help. I wouldn’t still be in this hobby if it wasn’t for fellow club members who took me under their wing and willingly volunteered to help me. But remember, you’re the one that ultimately has to work on the material that you select, so you are the one that must decide whether or not to pay the price asked. I hope this helps!

Polishing Channel Work
(from Owyhee Gem-12/99, Rock Chips-10/90, Rock Rollers 1/90)
To polish stones and silver together, as in channel work, use cerium oxide. Other polishes may scratch the silver.

Montana Agate – (from The Puget Sounder-11/99, Author unknown, HyGrader-5/98)
One of the most popular gemstones found today and used in almost every type of jewelry is the Montana agate. The main deposits of this agate are found in the river and bench gravels of the Yellowstone River from Huntley east down the river to where it flows into the Missouri . . .This agate has more variety of colors, types and figures than agate from any other known deposit in the world. These colors and figures found in the agate were formed mainly by iron and manganese oxides and sales, which were present in the hot water silica solutions which formed the agate.

How to Saw Montana Agate
(from The Puget Sounder-11/99, from Gem Cutting Shop Helps, Grindings 6/94, Rock Rollers 7/97, and Fox Rox News 11/97)
People not familiar with working with Montana agate have, perhaps, wondered how to “st-up” to saw the first nodules they acquire. Most Montana nodules are found in two shapes, flat and slightly curving, or round and elongated. As this material probably has rolled hundreds of miles down turbulent streams, nearly all of it is cracked, so take this into consideration when sawing to get the largest slab free from fractures.

First, look into the rocks with a strong light to determine which way the moss or banding layers lie. Light cuts taken off an end, or side, at right angles to the layers, will then reveal whether you should slab from end to end or side to side. Many people who are used to sawing thundereggs get used to sawing each nodule through the center to expose the pattern. While this method works well with nodules, it cannot be used to the best advantage with Montana material. It will probably ruin the best sprays as the larger and best ones usually lie toward the center. Sawing across them will render them valueless.

Only a very few specimens carry fine large sprays, so do not be disappointed if the first few do not have them. About the time you are ready to give up, one of the poorest looking pieces may have the fine spray you are looking for.

Polishing (via Owyhee Gem 8/99, The Rockie News)
When polishing – do not use a saucer, dish or pan and messy brush to apply the polishing agent. Such methods invite contamination. Instead, use a plastic bottle with a long tip. Put the polishing agent in the bottle, add water and a small stone, or buckshot (the purpose is to agitate and stir up the polishing powder when you shake the bottle). Shake well and squirt solution on the felt, leather or canvas. No contamination, no waste of polishing agent, and the polishing agent.

HELPFUL Display Case Hints
(Gems of the Rogue 8/98, Oregon Rockhound 6/98, Rock Chippers 6/98, )
Attractive mineral displays are often created with specimens shown at varying heights on suitable pedestals. An easy and inexpensive way to achieve this look is to use boxes in an assortment of sizes, all with flat sides and tops. Remove the lids, and use the bottoms of the boxes for display surfaces (unless the specimens are large and heavy). Ordinary cardboard boxes will do for small to medium sized specimens. Cover the boxes with contact paper or textured wallpaper in neutral colors, or paint them with a flat acrylic or latex paint. Arrange them in a pleasing pattern designed to show off the specimens in their entirety.

Make sure that each specimen looks as good as possible. For example. if you are displaying rose quartz with realgar just above it and to the left, and dioptase below and to the right, the rose quartz will appear pale and uninteresting because of its vivid neighbors. If the specimens are large and dramatic, wooden or Lucite boxes or risers are a better choice. Make box shaped risers out of natural wood, then stain or paint them. You could cover them with fabric suitable for displaying, such as decorator’s burlap. Using fine quality plywood is another option.

Attach specimen labels to the side of the riser, facing the front of the case. You can create labels using either material that matches the box, or Lucite or metal plates. Place them just below the specimen on the vertical front – labels placed on the horizontal tips are often difficult to read.

by Jon Sams with update by Don Esch

During the annual and quarterly cabochon contests held by the Willamette Agate and Mineral Society, there is one predominate error that seems to bother one and all. This, of course, leads to secondary errors that in the final sum total would give a Federation judge fits. Another important factor is that most of the members do not have the time, following a full work day, to grind and grind on a cabochon with a full dome. Hence, there are a number of members who would like to enter contests but hesitate to do. This, I am sure, is cause by the above mentioned factor. The method that will de explained herein is not only acceptable by Federation judges, if you decide to go the contest route, but will cut your working time by two-thirds once you have mastered this technique, and it is not really that hard to learn.

  1. Figure 1 is a prime example of a semi-flat dome. If you were to superimpose Figure 1 on Figure 3, you can readily see how much grinding is eliminated. Since most of the cabbers work in harder stone (Mohs 5 ~ to 7~), this is really a time saver. Also, a flat or semi-flat dome will hold the reflective beauty of the material much better than a high dome. (Opal is an exception. . to the above statement)
  2. Figure 2 depicts a cabochon with a rolled girdle line. This is strictly a no-no. Judges just shake their heads when they see such a fault. Some of this roll is cause by grinding, and some by the polish action. Let’s get into some of the simple things that make an poor cabochon into one of outstanding beauty.

    Most of us know before we start to make a cabochon, we would like to mount it into a finding. Rule number 1: The prongs of a finding should never extend above the girdle line. So, the obvious thing do is to measure the height of the prongs and set the girdle line accordingly. Most prongs are 3 to 3\ MM in height. Since there are 25.4 MM to the inch, one can figure the height with ease. A mounted stone with prongs bent over on top of the dome draws your attention to the prongs and not to the beauty of the stone. Therefore, the distance from the base line to the girdle should never be less than the height of the finding prongs. The Ideal dome is one that measures vertically ~ the distance from the base line to the girdle. Information such as this, and much more, is never published, but held in the heads of judges. This is one of the things that some times makes the exhibitor bleed and bleed. One must ask question after question to finally compile all of the facts that will give you a score of 95 or above. Rule number 2 (these are my rule numbers): The bezel or slanting edge of the stone, after it has been ground to template size, should be angled in from 12 to 17 degrees. This is to allow the prongs of your finding to grasp the stone firmly. The bottom edge of the bezel should always be back beveled at 45 degrees to eliminate all rough and raw edges caused by grinding. This bevel should always be polished. The dome entry to the bezel (known as the girdle line) should always be sharp and well defined (Fig. 1) and not as shown in Figure 2. Always strive to maintain a straight line of uniform depth to your girdle.

    In setting up to grind a flat dome, start with grinding around the edge above where the girdle will be, and in a sort of “peel an apple routine.” If you are making a 40 x 30, or any other size, always change the angle of your dop stick in relation to your stone, ie: When grinding opposite the long axis 40 MM) your dop stick should have a shallow angle and then as you come around opposite the narrow axis (30 MM) increase your angle. This will insure the correct curvature for the dome. Shape your stone with a silicon wheel to about ~ MM from your marked girdle line. Change then to paper of your choice. Each and every one of us has a different thought on this part of cabochon making. By using paper, which cuts a lot slower, you will eliminate scollop on your girdle line. If using diamond grind wheels, be sure to switch to next finer wheel before getting to these lines. Use a metal edged ruler and run the edge over the face of the dome while holding at eye level. If you can see only one point of contact as you move across the dome face, your curvature is correct. This method will show flat spots in a hurry. Using a worn out 600 paper will remove most to your grinding scratches. The next will sound a little odd, but it works for me. After I have used the 600, I put on a WELL worn 400 and grind at 90 degrees from the direction that I used on the 600. Always change direction of grind by 90 degrees when you change grits.

  3. Polish….Oh what a nasty word (sometimes). Use your own method of polishing, but add this….On the first few minutes of polishing, rotate our stone in the opposite direction that your buff is turning and in most cases, use considerable pressure….NOW….reduce pressure and rotate your stone in the same direction as the buff is turning. The results are sometimes astounding. The preceding also works well with diamond. Be sure that you polish the bezel first and then when you are on the dome….do not…roll over onto the bezel. If your do….this will cut our sharp girdle line and I would like to stress again….Always try for a sharp, well defined girdle. I sincerely hope that this short extemporaneous paper will cut your cabbing time and increase your enjoyment of this wonderful hobby.