I have been polishing c-plane sapphire using alumina slurry and have been getting around 12 um/hr removal rate. I am trying now to polish A plane sapphire, but my removal rate dropped considerably to less than 4 um/hr? Do the A plane and C plane polish differently?

Your results with polished sapphire are explaining the difference hardness C- and A-planes.

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I have been polishing c-plane sapphire using alumina slurry and have been getting around 12 um/hr removal rate. I am trying now to polish A plane sapphire, but my removal rate dropped considerably to less than 4 um/hr? Do the A plane and C plane polish differently?