Polishing a soft metal to a high degree of reflectivity is easy. You just keep rubbing it over and over. So at first glance it might have seemed off how the easiest metals to polish would be the last ones to be offered in a mirror finish. There is a good reason for this though.

While shining up a piece of lead (or indium) is indeed very easy to do, doing so while maintaining a specific shape really complicates things. That softness is in a very literal sense the weakness that is conspiring against the form integrity of the object being polished. Try taking a normal cube and rubbing it against a piece of paper and you will see that while, yes, that side polishes up beautifully the mere pressure of hand holding it has caved in the sides and formed gummy burrs on the edges. Do that for all six sides and you’re left with a gorgeous little formless lump. The more you try to fix it the worse it gets.

There were a number of potential solutions to this problem. One was to have a very precisely made mold that was itself polished to a mirror finish into which the target metal could be cast (soft metals also happen to have low melting points) but the costs involved in preparing that mold were very costly. Worse, it would have needed to be done in a partial vacuum to avoid air becoming trapped during casting which would also have increased costs further. So this route was shot down purely as a business decision.

Another option would have been to take the normally completed cubes and have them hand polished in a contraption that held them securely while exposing only one side but informal tests were not promising. The added cost of the labor would have made the project unprofitable too anyway.

We had all but given up when an extrusion process developed in the making of the recently introduced alkali metal cubes was just as effective with other soft metals too. We were happy to ride those coattails and can finally introduce indium and lead in the coveted mirror finish!

Because of the extreme softness of indium we have elected to have these cubes housed in glass and glued in place to avoid movement. Even the mere act of handling them is all that’s needed to permanently mar the finish :-(