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Sample preparation for ore microscopy - part 2

To be honest: grinding and polishing are a science on their own. It needs quite some time to figure out how to do it right as the know-how needed is not very well described in literature. Ore microscopy seems not to be fashionable anymore as even the material suppliers give good instructions for metallurgical samples and almost nothing for minerals and ores.

All samples here are grinded and polished by hand using a Chinese grinder polisher with the nice name MoPao 160E. The machine has changeable aluminium disks on which the diamond disks or polishing cloth is glued. The machine is solid build, reliable and fun to work with. The stereo microscope in the foto below is a Leica MZ6 used to check the results to make sure one step is completed before proceed to the next one. Usually this is not necessary but advisable for important samples.



-> 125 um nickel-bonded (Buehler Ultraprep)

This step is important to remove all surface deformation from diamond cutting. The following steps then just remove the marks from the previous steps. In this step it also make sense to remove all sharp edges as they later might damage the polishing cloth. I even remove them on the back as the sample is easier to hold during grinding and polishing.

-> 20 um nickel-bonded (Buehler Ultraprep)
-> 6 um resin-bonded (Buehler Apex) or SiC FEPA 4000
-> 3 um Diamond Suspension (Buehler Metadi Supreme) on a hard polishing cloth
-> (Buehler Texmet)
-> cleaning of the samples in an ultrasonic bath

Extreme care should be take to avoid any carry-over from one step to the next, especially when changing to suspensions. Each disc should have its own brush for cleaning. By the way: after the 6 um stage the grinding of the slabs stops. The highly polished surfaces hide more details than they reveal, and scanning them for documentation becomes difficult.

The beauty of grinding discs I: Buehler Apex Color



-> 0.3 um Aluminium oxide-Suspension (Pieplow & Brandt SEPP 0.3) on a hard polishing cloth
-> (Buehler Texmet)
-> cleaning of the samples in an ultrasonic bath
-> cleaning of the samples with water and soap
-> rinsing with ethanol, followed by immediate drying

After drying ore microscopy should start immediately as the surface will start to oxidize which might in the worst case be a matter of minutes.

A final remark: no grinding and polishing times are given and no revolutions per minute for the polisher. Too many parameters including the sample itself influence the polishing time. A rough estimate is about 1-5 min per step. Generally all attempts to shorten the process will result in failure.

The beauty of grinding discs II: KGS Telum pattern


Having the sample prepared, we just need to mount it on a glass slide with some Plastilin and with help of a sample press. Then we can start research....