Polishing By Ralph Mathewson

Faceting Hints

"Polishing"

by Ralph Methewson (President of the US Faceters Guild), August6, 1998, © Copyright
Edited & Published on the Web by Lance A. Kanaby

POLISHING

by Ralph Mathewson

For stones with a hardness of 7 and under, such as feldspar, Mt. St. Helen's glass, opal, all colors of quartz, tourmaline and others, I use a Cerium Oxide Dyna-Disc. Peridot and garnet are an exception. Peridot has hardness of 7 and garnet has a hardness of 6 1/2 to 7 1/2; I polish them with diamond, because they will not polish on the cerium oxide lap. For stones above 7 in hardness, I polish with diamond.

CERIUM OXIDE DYNA-LAP

I use a slow drip of DISTILLED water on the cerium oxide lap. The time frame is about one or two drips for every five seconds -- Use no additives in the distilled water. The lap should stay barely moist. Caution -- Never let it get dry! If the lap becomes dry, the cerium oxide will powder-off. Run the lap at the slowest possible speed.

Hand Pressure

I use very light pressure and sweep the stone across the lap, if the stone is grooving, you are probably holding it in one place too long. Be sure to sweep the stone across the lap. This procedure should give you nicely polished, flat and sharp-edged facets.

Scratching

If any scratching occurs, take the stone off the lap immediately. You can usually stop the scratching by turning the lap up full speed with the water turned up to a full stream. Run your fingers over the lap to dislodge the particle that is causing the scratching; reverse the lap and do the same procedure. This almost always takes care of the problem, but if it does not, take the lap to the sink and scrub it with water, dish soap and a fine brush.

Other Problems

One of the problems you can experience with quartz is a phenomenon that is called a 'herringbone effect '-- a configuration that sometimes can be observed naturally in some quartz crystals. If the stone is swept lightly across the lap, you can usually get rid of it; however, if the 'herringbone effect' does not disappear, then reverse the lap rotation. Be sure to sweep the stone across the lap, and be sure not to work the stone too long; otherwise, the 'herringbone effect' may reappear in a different orientation. Usually if you quit precisely at the right time, the 'herringbone effect' will disappear -- sweep a little and look a lot!

CERAMIC LAP WITH DIAMOND

In the past, I used 50,000 diamond spray. Since I had less than a quarter of a bottle to begin with, I soon ran out. I went to the sink, scrubbed the lap with dish soap (New Dawn), lava soap and vigorously scrubbed with a fine stiff brush. I already had a full bottle of 100,000, so I used it to charge the lap. Both the 50,000 and the 100, 000 did a fine job polishing, but not for CZ, especially when I had to cut CZ for competition.

The minor scratching on CZ would not go away even with the 100,000. (This kind of scratching can usually be seen on CZ commercial stones.) After many unsuccessful, exasperating attempts at solving the minor scratching with the 100,000, I decided to try some 200,000.

After re-scrubbing the lap, I charged it with 200,000, and within a couple of passes over the newly charged lap, the minor scratching was gone. I have kept the lap charged with 200,000 ever since.

A Suggestion for seeing those minor scratches: Hold the stone right between shadow and shine under magnification; the scratches should beeasily seen.

Charging the Lap

I shake the spray bottle well to get all of the diamond into suspension. I then open the spray bottle, and with the spray stem as a dip stick, I touch the stationary lap eight or ten times around the lap. The total amount of diamond solution used is from 1/2 to 3/4ths of a drop.

I then start the lap at the lowest speed possible and spread the diamond evenly with a razor blade. The blade is held and dragged at a low angle. I let the lap dry for about 20 minutes before using. If time allows, I let the lap dry over night; this allows me to place slightly more diamond on the lap. This extra charge will greatly extend the polishing time.

Lap Condition

If the lap is charged properly, polishing is immediate. (I will run the lap as slow as possible.) If too much diamond is used, the stone will float on top of the lap and will not polish well. A solution is to wipe off the excess diamond with a lint-free paper towel. Learn quickly to charge the lap properly, because wiping a newly charged lap wastes the diamond. You want the charge to last as long as possible.

Wet and Dry Condition

Do not use water during polishing. When I refer to "wet or dry," I am referring to the condition of the lap, on which the diamond extender or spray may be fresh or dried out. If the lap is too dry, the diamond will ball up and scratch; if too wet, the stone will float on top. When it's just right, it will cut the polish in fast.

When the lap is almost dry enough, you can polish by speeding it up from 30 rpm (my slowest rpm) to about 80 or 90 rpm. When the lap dries out properly, you must quickly return to 30 or 50 rpms; otherwise at 80/90 rpm for any length of time, severe scratching will occur, and/or excess heat my cause the stone to fall off the dop. What happens is, the lap will dry out too fast, which in turn causes the diamond bort to ball up. The result is real plow-furrows.

Please remember, the ceramic is already quicker at polishing more than most other or all other laps. So do not rush it, if you do, you will not like the results.

It took a lot of effort and practice to come up with a quick preparation for polishing, that is, the proper charging of the lap with the correct amount of diamond and the exact wet or dry condition. In time and with a little practice, it will become easier and quicker for you. When the polishing conditions are perfect, that is, the lap is charged correctly, the right amount of extender is on the lap and there is no contamination, several facets can be polished without doing anything to the lap.

Section "A" -- Polishing

Watch very carefully to see if any minor scratching takes place. If it occurs, stop polishing immediately. Swing the quill and the stone out of the way. Back the mast off so you will have a little room. Turn on the lap at its slowest speed, and hold a razor blade facing into the turning lap. Hold it so it will cut off most of the build-up on the lap. DO NOT TRY THIS PROCEDURE ON ANY OTHER LAP EXCEPT A CERAMIC.

"Build-up" is excess residue, which consists of ground stone and diamond extender. The residue forms a kind of scum or sludge on the surface of the lap. The lap should not be too dry from lack of oil. It should take only a couple of rubs across the lap to get rid of the minor scratching. You should be able to cut the polish in on several facets until, once again, too much build-up re-introduces minor scratches. The razor blade must be used again.

With practice, and with the feel of the stone on the lap, I can usually sense before it begins to scratch, if so, I immediately stop polishing and cut off the build-up. If it is necessary to cut off the build-up many times, the lap will become too dry. However, chances are, there is still enough diamond left to cut in a fine or competition polish on many more facets. All you need is a little lubrication.

Section "B"--Putting on Extender

With the lap stopped, put a very small amount of diamond extender on the lap. I use Super Lube for my extender, because it contains Teflon. The ingredient Teflon seems to make the lubricant last longer. It cuts in the polish with a drier lap and prevents scratching over a longer period of time. I put about 1/4 of a drop on my finger and go around the lap touching it in several places. I turn on the lap at the slowest possible speed, take a razor blade and spread the extender evenly. It's the same way that I spread the diamond spray. I am very carefully not to put too much extender on the lap. If I get too much lubricant on the lap, I know the stone will plane, and as expected, it will not polish well. A solution is to wipe off some of the lubricant with a lint-free paper towel. However, learn quickly to use the right amount, for when you have to wipe the lap, you are shortening the time that the lap will stay charged.

Work again and again between Section "A" and Section "B" until the diamond is no longer in sufficient strength and quantity to polish well. When these conditions appear, recharging is mandatory.

Recharging

Please read the last paragraph once more. Keep in mind that you have been alternating section "A" and "B." Polishing is not going well, due to the diamond losing its quantity and its strength. Yet, the proper dry condition for polishing is still in effect. It's at this moment, just before minor scratching begins, which is due to the lap getting drier, that the optimum time for recharging occurs. It is also at this time that the lap is not only in perfect condition for receiving diamond, it is also capable of receiving a much larger charge.

In time and with practice, it will become easier and quicker for you to be able to determine that almost magic instant when the time for recharging is just right. With practice and with the feel of the stone on the lap, you will be able to sense the moment just before minor scratching begins. If you are doing competition or fine custom cutting, the number of stones you may be able to polish varies from 1/2 to 2 or 3 stones. However, if you are cutting commercially, you will be able to polish a lot more, because the lap condition necessary for perfect meetpoints and competition polish is not mandatory for most commercial faceting. Minor scratching and less-than-perfect polish is accepted without question.

THE TABLE

Just before you are ready to polish the table, and with a few facets left to go; (A) add extender to moisten the lap, and polish 1 or 2 facets, or, (B) if needed, recharge the lap at this time and then polish 2 to 4 facets.

Both 'A' and 'B' not only allow for excellent pre-table lap conditioning, it is also an important time to inspect for scratches. Either way you go, the chances are, scratching on the big table facet will be greatly reduced.

The table polishes with a slightly wetter lap than the rest of the facets, and sometimes, you may find it helps to work closer to the center of the lap, where it turns slower.

THE CERAMIC LAP, PER SE

No lap can produce flatter or sharper edged facets. It is one of the faster, if not the fastest lap for cutting in the polish with diamond, but at the same time it is much less forgiving than any metal or plastic lap.

Scratching

When there is anything on the surface that will scratch, the scratch will be magnified. Even a small bit that would cause only a medium scratch with metal or plastic, will produce a major scratch with the ceramic. I do not have to wash or scrub the ceramic lap to get rid of the contaminants. The razor blade seems to do a good job of doing that. It cuts off contaminants as well as the built up sludge of ground stone and diamond extender.

Lap Protection

When the condition of the lap is just right for polishing, and if I have to leave the wheel for awhile, I put a piece of plastic wrap (Saran) over the lap to keep it from drying further. One exception to this would be, not to cover the lap, in order to let it dry some, that is, if it is too wet with diamond spray or extender.

I also store my polishing laps in ziploc gallon bags to keep them from drying and becoming contaminated. Label each bag and be sure to put each lap back under its correct label.

TIPS FOR OTHER LAPS

Do not put a light directly over your machine. The ceramic socket that the bulb screws into can flake off tiny bits that are as hard as your best sapphire or ruby.

When you wipe off the stone to look at the facet, pull the quill away from the lap. Do not drag the lint-free cloth or lint-lint-free paper towel over the lap, because you can easily introduce contamination. If you are called away from your machine, be sure you do not bring contaminates back with you on your arms, clothing, hands, hair, etc.

When you are polishing, and if you need to adjust your mast or index-gear-cheater, make sure you cut the polish all the way across the facet on which you are working. If you do not, you will leave a shoulder, a ridge, somewhere on that facet. If it's very pronounced, in certain lighting situations it can be seen as an ugly double facet. {A very costly mistake, if the stone is to be entered into a competition.}

METAL POLISHING LAPS

I do not use any water on my metal laps when polishing, and I run the laps at my machine's slowest speed. I have a tin lap and a type metal lap. I never use a razor blade to clean these laps. With the razor blade turned against a metal lap, it would catch the lap, quickly gouge it and could possibly cause a severe slash on the finger.

However, to charge a metal lap, or to put extender on, I always use the razor blade to spread the diamond spray or extender in the same manner, as I do for my ceramic lap. Since I cannot use a razor blade to cut off the build-up of sludge, I am obliged to use lint-free paper towels. Usually, I wipe the lap, either when it is not polishing as it should, or before the facet I am working on begins to get minor scratches.

I can tell by the feel of the stone when this needs to be done. The stone will give a kind of dry pulling-feeling when it is put on the lap, and also there can be chattering and squeaking noises.

These negative conditions for successful polishing usually take place after polishing a number of facets. Please remember, if the stone is not polishing well, or if the lap begins to grab the stone, or if there is chattering, the lap is too sludgy or too dry. Shortly after minor scratches begin, deep scratches are inevitable.

There is probably enough diamond left to polish more, but the lap is too dry. At this time it will need lubrication. Again I prefer SUPER LUBE because the Teflon in it seems to make the charge last longer. I use exactly the same amount of Super Lube and the same process for putting it on, as I do for my ceramic lap.

Time For Recharging With Diamond

When the lap has just the right amount of extender on it and refuses to polish, it is time to recharge. I use the same exact procedure, as I do for the ceramic lap.

BREAKING IN THE CERAMIC

My experience is limited to breaking in only one ceramic. I used a Norbide-carbide lap-dresser with 50,000 diamond and worked it quite extensively over the lap. The lap was at the lowest possible speed. I charged the lap with the same procedure I normally use for charging a ceramic, except I use about twice the amount of diamond. The lap, being new, was completely void of diamond and extender oil. I worked about one half a day with the Norbide lap dresser.* Then I dopped a synthetic sapphire, cut in some facets and tried the lap at polishing. It polished well.

It is my hope that you will find the above procedures, suggestions and comments worthy of consideration. If you become a better faceter because of them, the article is worth all of the necessary effort, it took to write it.

Ralph Mathewson

*Darling Abrasive & Tool, Inc
1032 Edward's Rd.
Burlingame, CA 94010
(415) 343-9995

The End