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Equipment needed:

• Round slides or leucite/epoxy sample mounts
• leucite slide holder
• 100, 220, and 600 grit magnetic grit laps (in MSEC thin section lab)
• 30, 15, 6, and 1 µm diamond powder (in probe prep lab)
• distilled water, cloth laps and glass mounting plates

It is difficult to write a generalized polishing procedure, because the length of time needed for each step is variable from sample to sample. However, here are some general guidelines that may be helpful.

1. Once sample has cooled to room temperature following epoxy curing, mount in leucite sample holder. Sample may need to be held in with a small piece of tin foil.
2. Find the 100 grit diamond magnetic grinding lap and the wheel. Put the wheel on the polishing mount and place the grinding lap on the wheel.
3. Turn the water on to a thin stream. Turn on the wheel and adjust the speed. Grind the sample down until most of the grains are exposed, but not ground down too far. DO NOT press down hard on the lap, but hold the sample down with about the weight of your hand. When you're done, less than half of the average grains should be ground away. or else they could be ground to nothing on the next grinding step. Take care at this step to keep the sample flat. Look at the sample occasionally, and if it has become wedged or domed, attempt to correct the problem. Once the sample is done, rinse the sample (still in the sample holder) in tap water. Dry the lap carefully and put away.
4. Find the 220 grit diamond lap, and mount onto the wheel. Remount the sample, turn on water, and grind for about 3 min. on the 220 wheel. Again, try to keep the sample flat. Rinse the sample when done, and dry lap.
5. Find the 600 grit diamond mesh. Mount lap, turn on water and grind the sample for 3 minutes on this wheel. Once this step is complete, the sample should be removed from the sample holder, placed in a small beaker of water, and ultrasonified for about 20 seconds. Rinse the sample holder in tap water. Dry lap and wheel. Move to the probe prep lab.
6. Find the 15 micron polishing cloth. This should be stuck to a glass backing plate and stored in a ziplock bag. Remount the sample in the sample holder. Put a pinch of 15 micron diamond powder onto the cloth, and wet it with distilled water. Polish the sample for 3 minutes, changing the sample orientation occasionally, and applying moderate pressure. Remove the sample from the holder and ultrasonify for about 20 seconds.
7. Find the 6 micron polishing cloth. This should be stuck to a glass backing plate and stored in a ziplock bag. Remount the sample in the sample holder. Put a pinch of 6 micron diamond powder onto the cloth, and wet it with distilled water. Polish the sample for 3 minutes, changing the sample orientation occasionally, and applying moderate pressure. Check the sample now and then with the microscope to see how the polish is progressing. You want to achieve a sample surface with few pits, and an even network of small scratches. If the sample is still pitted at the end of 3 minutes, keep polishing for another 3 min. If, at the end of the second 3 minutes the sample doesn't appear to have progressed at all, get the 15 micron polishing cloth and do 3 minutes on that. Then, ultrasonifiy and go back to the 6 micron cloth. When you have achieved the no-pit/even-scratch surface, remove the sample from the holder and ultrasonify for about 20 seconds. Return the 6 micron cloth to the ziplock bag.
8. Find the 1 micron polishing cloth. Prepare in the same way as the 6 micron cloth, using the 1 micron diamond powder. Polish the sample for 3 minutes on this wheel. Rinse the sample. Return the wheel to the ziplock bag.

Notes:

If polishing a number of samples, it is easier to go through each polishing step with all of the samples before beginning the next step.

The 6 and 1 micron polishing cloths are easily contaminated, and once contaminated will not give a good polish. Always ultrasonify the sample and rinse the sample holder before using these cloths, be careful not to spill anything on them, and cover or bag them when not in use.

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Revised: 12 May, 2008

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Copyright © 2007 - 2008 New Mexico Bureau of Geology & Mineral Resources unless otherwise specified.