No lap creates more ďfear and loathingĒ than the Ceramic Lap. With the same Mohís hardness as sapphire, ceramic laps are the hardest polishing laps you can buy. Therefore, they create the flattest polished facets of any lap.
Diamond particles become partially embedded into the surface of most polishing laps. Ceramic laps operate differently, because all the diamond particles remain loose on the surface of the lap. Since the diamond stays on the surface of the lap, it is almost impossible to have too little diamond on a ceramic lap. This makes loading ceramic laps with diamond a challenge. Too much diamond is the most common problem people have with ceramic laps.
One way to get around this problem is to dilute your diamond spray. I learned the following method from my friend Paul Head. He is able to polish just about any material except quartz on his ceramic lap.
Purchase sprayer bottles at your local pharmacy that are the same size spray diamond comes in. Put Ĺ teaspoon of well-shaken spray diamond and Ĺ teaspoon of extender fluid into the spray bottle. Top off the bottle with denatured or grain alcohol. This substantially reduces the amount of diamond you will be applying to the lap with each spray.
If you are starting off with a new ceramic lap, prepare it with a small amount of graphite. Put about 1/8 teaspoon of powdered graphite into a spray bottle and fill to the top with alcohol. Shake well and spray on to a rotating lap. Immediately rub the graphite/alcohol mixture into the lap and wipe off as much excess as possible.
Your lap is now ready to receive diamond. While the lap is rotating at a slow speed, spray your diluted diamond mixture on to the lap from about 10 inches away. Take a paper towel and rub the lap to evenly spread the diamond over the lap. You will probably have too much diamond on your lap!
While the lap is running slowly, very carefully place a razor blade at the center of the lap. Press the blade into the lap with a light pressure and slowly move it toward the outside edge of the lap. Be careful, razor blades can be sharp. You still have too much diamond on your lap!
Get a clean facial tissue or paper towel well dampened with alcohol. With the lap rotating, start wiping the center of the lap and slowly move toward the outside edge of the lap. Open up a fresh portion of your tissue, re-wet it, and repeat the process. You are finally ready to start polishing with your new ceramic lap.
Donít be discouraged if your new ceramic lap is slow in polishing. Ceramic laps can take a long time to break in.
Another technique for setting up ceramic laps is rub tin/lead solder onto the surface of the lap. Make sure that any oxidation on the solder is cleaned off before loading the lap. The oxidation can create a problem with contamination. Also make sure that your solder doesnít have a flux core, because the flux can cause problems in polishing. The thin tin/lead coating offers some help in reducing the problem of your ceramic lap becoming overloaded with diamond.
A fine pre-polish is a must with ceramic laps. Donít be surprised if you have to cheat to get your facets to line up on your ceramic laps. Ceramic laps tend to be the truest running laps available, so small inaccuracies in your pre-polish lap will show up when you change over to your ceramic lap for polishing. Some people get around this problem by also using a ceramic lap for their pre-polish.
Keep your lap clean and wipe it down with alcohol before using or changing to a new tier of facets. I have found that best results are obtained with light pressure and slow speed.
If you canít seem to get the excess diamond off your ceramic lap with alcohol and a razor blade, (or if it gets contaminated) you can clean it off with lava soap.
I only use my ceramic lap for the hardest stones such as sapphire and chrysoberyl. I find that the finicky quality of ceramic laps is too much of a hassle on most stones. I canít say that Iím a fan of my ceramic lap, but I donít quite hate it either.
You will find that most faceters have strong feelings toward ceramic laps. They either love Ďem, or they hate Ďem.