Charging cutting laps and scoring polish laps are two entirely different procedures which we faceters have to perform at certain times. One procedure does not do the job of the other. One procedure is done so that certain of our laps will do a good job of cutting the gem material in a way that we want it efficiently done, and the other procedure makes our polish laps work efficiently. First I will discuss the charging of cutting laps, and then later in this article I will get into the scoring of polish laps.
Charging Cutting Laps
It is primarily with the copper lap that most faceters experience the process of re-charging a lap. The copper by itself does not cut facets on the gemstone. We need a diamond abrasive to do that job. Copper is a metal which readily accepts the diamond that we embed into it. Although permanently charged laps can be purchased in many different grits, the much more reasonably priced copper lap becomes the choice of some faceters simply because of the more controllable results. Yes, it takes time to occasionally re-charge the copper lap, but I prefer to do most of my pre-polish cutting on a fine-grit charged copper lap.
To start with the re-charging process, I place my copper lap flat on a table, with a paper towel under the lap so it can catch any messy residue. The paper also helps keep the lap from sliding or moving. Some people have the lap on the faceting machine during re-charging, but that seems like a way to sling off the residue which I am not interested in doing.
First, I apply about twenty drops of Crystalube extender around the stationary lap. With the tip of my index finger I spread the extender around so that the entire lap is coated with the “oil”.
Then I apply the 1800 grit diamond to the stationary lap, in approximately twenty small dots around the lap. A tiny push on the syringe plunger gets a bit of diamond available to touch the lap with. This form of diamond that I like to use is not a powder, which would be wasteful and likely to contaminate the entire area. It is in the form of a plastic syringe filled with” grease” that contains the diamond. The syringe contains enough diamond to re-charge an eight inch copper lap many times.
Again I use the tip of my index finger to first streak the dot of diamond grease towards either the lap center or the lap outer edge, whichever the dot is farthest from to start with. Then I swirl the grease around with my finger tip until it is distributed all over the lap, especially right out to the outer edge where you may have to cut girdle facets. The outer one-half of the eight inch copper lap needs far more diamond than the half near the lap’s center hole. Most of the cutting will be done on that half near the outside of the lap.
I am now ready to actually get the diamond embedded into the soft copper metal. This is where the roller bearing tool does the job. The tool that I bought long ago has a handle on it. It also has a metal framework to hold the five-eighth inch diameter by one and three-quarters inch long roller. This wide (long) roller bearing is easy to keep flat on the lap during the time I need to apply pressure on it, to drive the diamond into the copper. I am sure that one of these tools is available for you at the many lapidary supply houses, or at the Shows.
As I hold the handle of the tool with one hand, I apply a firm pressure on the bearing and its framework, as I push and pull back and forth all over the stationary copper lap. Primarily, I guide the tool back and forth from the outer edge towards and over the center hole across to the far edge of the lap, and then back again. I do this from all angles around the round copper lap to be sure that all of the diamond has felt the pressure.
That was the first try. Now I swirl the black messy residue around with the tip of my index finger again. Once more I do the pressure work with the roller bearing tool. That is the second time. I do this same procedure for a third time, so that I am using all of the diamond that is available. I do not add any extender fluid or diamond grease to what I had put on at the start.
If the diamond is not into the lap now, it is not going to be later either. So it is time to get rid of the messy residue. The residue would get slung off when the lap is installed onto the machine and revolved. The residue interferes with inspection of the facets as you cut them. The residue has to go.
To get rid of the residue I wipe the lap off with a paper towel. Next, I wash the lap with Lava soap and rinse with water. Most of the mess will be gone, but the lap with still be coated with a light film of oil. The oil interferes with facet inspections. I get the lap ready for use by dampening a rag with paint thinner (mineral spirits), and proceed to wipe off the entire dop. At this point the lap is ready for use on the machine.
Actually the paint thinner will still leave a finish that is not entirely clean, but clean enough. If you really wanted the surface to be dry and clean, you could wipe the lap with a rag dampened with lacquer thinner. That is what I would do if I intended to paint the lap. I have chosen to cut facets instead.
I have found in my experience that the permanently charged laps often do not actually cut at the grit that the manufacturer has labeled. And sometimes those laps leave rows of deep scratches on the gemstone. The permanently charged laps do wear out, and are not re-chargeable.
I do have three permanently charged laps of 325 grit, an old 3000, and a newer 3000. The newer 3000 cuts like a 600, when compared with the old 3000. I guess the manufacturers cannot really control the grit size with much accuracy.
I purchased my copper lap at the time that I purchased my Ultra-Tec faceting machine, approximately thirty years ago. That remains the only copper lap I have ever bought, and I use it often. When new, it was already charged with 600 grit on one side and 1200 grit on the other side. I also bought the roller bearing tool for pressing the diamond into the lap. All of this was at the recommendation of Mr. Grieger, who was an important authority for faceters in those days. As I remember, I paid Mr. Grieger about three-hundred and fifty dollars for all of the above items…including the Ultra-Tec…eat your heart out you present day newcomers. Those were the good old days for faceters.
In reflecting back on the years, I have never re-charged the 600 side because I soon decided that the 1200 side could become contaminated from the nearby coarser grit. My advice is for you to decide to dedicate certain laps to do certain jobs. Do not expect one lap to do the job of another. It is a good idea to keep each lap in its own zip-top plastic bag, which is changed from time to time. My view has been that if two grits are desired, the facetor should buy two copper laps and use just one side of each of them.
Copper laps used to be the most inexpensive way to go, which is not necessarily the situation these days. But, since a copper lap will last a lifetime, it is very inexpensive in the long run.
As the years have gone by, I have re-charged my copper lap with 1800 grit diamond, instead of the 1200. This was done so that the lap would leave a much finer finish on the facets. My usual practice has been to go from the copper lap to the polishing phase with most gem materials. I achieve extremely good facet meets with the copper 1800, and get a finish that has few scratches of any size. Even so, I like the 1800 when it is not sharp, after it has had some cutting done to “break it in”. Freshly charged laps are always relatively sharp to start with.
I do not want to have to polish and polish, just to get the meets in properly. I spend most of my time on a stone in the polish phase as it is, so doing a good job at achieving meets in the cutting phase is time well spent. The polish phase is what determines the quality of the finished gem, nothing else comes close to being as important.
On some materials I have used my well-worn 3000 grit permanently bonded lap to do the pre-polish final cutting. I use the new 3000 for roughing out some materials. My stressing having a fine grit for final pre-polishing comes from my chosen field of faceting, which is cutting for competition. If the facetor is in a hurry, all of my methods will be of no interest. On the high level competitions nothing much gets by the judges.
I have not experimented with charging copper laps with the coarser grits that are required for pre-forming a gem, or for first getting the main facets cut for a stone, or when a great deal of material needs to be gotten out of the way. My advice is to buy one of the permanently charged coarser laps for those purposes. Keep the fine grained copper laps for pre-polish work.
After a period of use, the diamond will wear away. You will spend longer periods of time to complete cutting a facet. You may notice that bits of copper streaks can be seen on a facet. It is then time to once again re-charge your copper lap.
Scoring Polish laps
The main concern in this article has been the subject of re-charging copper laps. However, I do the same thing to a degree with my tin lap, and my typemetal lap. But with these two laps I am polishing facets. Polishing is really cutting away material, but in an extremely fine quality way.
On a trip to the 1992 IFC Competition at Perth Australia, one of the Australian faceters clued me in on an Australian made typemetal lap. I bought one of the laps there, and it has proven to be a very good lap for flat and well-polished facets, as required in the World Class competitions.
I already had owned a tin lap for many years. A tin lap also helps one obtain flat and well-polished facets, with many gem materials.
I scored the surface of the typemetal lap only very slightly when I got it home. I have never scored it again, because the scoring did me no favors. It left parallel polish lines upon close inspection of the gems.
The tin lap has been scored many times, but is not ready for my use until it has been worn in quite well. The scoring gives you very fine parallel lines which can be found by the critical judges.
As I have said above, the typemetal lap is never re-scored by me. Neither is the copper lap. The tin lap is re-scored from time to time. Both the typemetal and the tin laps could be embedded with diamond such as I have described above with the copper lap, but I have chosen never to do so with a tin lap. I use polish agents and water on the tin lap.
With the revolving typemetal lap I use a short burst of 100K diamond spray followed by medium pressure with a Norbide Dressing Stick, to embed the diamond into the metal. If heavy pressure is used on a metal lap it can result in tearing the lap…so be reasonable. This gives one a polish lap that works very slowly but does an excellent job, when a well polished and scratchless finish is needed. I use this lap dry, except for the diamond being there and the lubricant that the manufacturer puts in the spray can.
With the tin lap, I usually am putting a touch of Linde A or another polish powder (agent) onto the turning wet lap, and then polishing on that. No embedding of Linde A is attempted. I use lots of water drip as I polish with this lap. With this lap I am not attempting to polish the very hardest gem materials.
Also to be considered is the ceramic lap, for use in polishing the very hard gem materials. Of course I do not score this lap. I do polish with it using the same system that I have described above with the typemetal lap…in other words I spray on a tiny bit of 100k diamond onto the revolving lap, followed by pressing the side edge of a Norbide Dressing Stick onto the turning lap so as to break down the larger diamond pieces, and to try to drive the diamond into the very hard ceramic lap.
Not much diamond (if any) is going to penetrate a ceramic lap, of course. The pressure from the Norbide tool helps break down the larger chunks of diamond to a smaller and more useful (uniform) size. Do not spray the ceramic lap with a lot of diamond, because then your gemstone will just slide along on top of the lubricant. The diamond has to be fine “cutting” the hard materials in order to “polish” the facets.
The ceramic lap along with diamond spray results in a different situation than that of all of the other laps and polish agents. Here we are just doing very fine grinding (cutting). With the other methods we are making gem material “flow” or “melt” (depending upon the current feelings of the scientists). I use the ceramic lap and the typemetal lap to polish the harder gem materials.
A scored lap is prepared so that the polish powder or agent will more easily stay on the lap, instead of being slung to the side and off somewhere. A lap is also scored so that less heat is created because of the tight space between the gem material and the lap. No lap is scored with the idea that you are driving the diamond into the lap. That procedure belongs to re-charging of laps. When it is time that the tin lap needs to be re-scored, I complete the following procedure.
With the tin lap installed on my faceting machine and the lap turning fairly slow, I use a tool for making small grooves or marks into the tin. This tool was purchased at one of the gem shows many years ago. You will be able to find them still stocked with dealers. The tool has a wooden handle and is about nine inches long over all. The tip of the tool has a little wheel made of a hard metal, which makes the gouges into the lap metal. The little wheel revolves as it is pressed down upon the turning lap. Believe me, the bits of metal fly off as the tool cuts into the lap…so not much speed is needed in the lap’s revolutions.
The tool is guided back and forth from the outer edge of the lap to the lap center, and back out again. Go back and forth a bit until the entire lap is evenly scored. This leaves a lap that is too rough to suit me. The many metal edges will leave scratches on a facet if you try to polish at this point. So again, I try to soften a fresh lap, I want to wear it in.
After I have cleaned the faceting machine and have washed the lap well, I install a piece of quartz that is doped to a dedicated dop and chuck just for this purpose. The quartz has a large flat facet on it cut to 42 degrees. I use lots of water drip as I press the quartz against the revolving tin lap. I go back and forth to knock down the higher pieces of the metal edges. I am smoothening up the lap. No powders used, just lots of water drip. After removing the lap again and cleaning everything up well, the re-scored lap is ready for service. Even now, I will be breaking in the lap further with the use of the Linde A, or another powder agent. Then the lap will be ready to do the polishing on a competition stone.
Polish laps should certainly each have their own plastic bag for storage. And even with the cutting laps, it is my feeling that all laps should be stored in a vertical way. To stack laps flat, one on the top of the other, will certainly help to embed unwanted particles into the laps.
Once again, I want to remind everyone that I am making suggestions for World Class cutting and polishing. In no way will my methods work or be practical for production cutters.