At room temperature you are working at  about 3/4 of melting point. That is not normally chosen for grinding operations. Perhaps you can deep freeze it with  liquid N2 or CO2 and grind it in a cold condition and use only soft grinding  material like clay, limestone, chalk ect.

b.r. Hartwin Weber

As Dr. Weber suggested: work on a cold plate between 5-10 degrees Celsius.

But, I would not recommend clay, chalk or limestone, because the fine loose particles would be squeezed into the soft indium surface.

Instead, I'd like recommend using the so-called

MICRO MESH SANDING SHEETS WOODWORKERS KIT

by Micro-Mesh (registered trade Mark). The particle sizes vary between 4000-12000 mesh (grit).

These abrasive cloth have the distinct advantage that the abrasive grains are embedded in a resilient pad and do not squeeze into the indium.

For final polishing, I recommend a smooth Linden tree wooden disc and pure water.

Best regards,

Guenter Grundmann

Electropolishing was recommended for indium or In-based alloys; either using diethylene glycol monoethyl ether with added conc. HNO3 and HCl (75:5:2 vol ratio) as electrolyte, current density: ~ 0.45 A/cm3, voltage: ~ 50 V dc, at 20 ºC, using Al cathode; or methanol with added conc. HNO3 (2:1 vol / vol), 0.30 A/cm3, ~ 45 V dc, at 20 ºC, 1-2 min.

Cf.: George F. Vander Voort, "Metallography: Principles and Practice", ASM International, 1999; p. 574.