Some degree of polish is of course standard. And after all, wouldn't your army look unprofessional if they had rough steel armour?
I've got the feeling that Isabel would feel the troops looks far too unimpressive if they didn't at least have a satin polish.

We can't go around and look like filthy mercenaries now, can we?
It's the personal troops of the De Reimers we are talking about here. They need nice shiny armour, impressive capes, fancy swords, and probably some training as well...
:P

However you could have it that they are in unpolished gear as a thing, to look more intimidating.
Do note however, that steel keeps from rusting better, the more polished it is. Just a thing.
But regular maintenance with oil will also remedy rust. So the intimidating thing can easily be done.

However troops in shining plate is also intimidating.

On a sidenote, here's an example of satin polished armour, with latten decor.
https://s-media-cache-ak0.pinimg.com/564x/00/46/2d/00462dfce76662f6246cbdb71ddf52da.jpg
Satin polish doesn't take too much effort to get going, and the polishing students need to train anyway.

Also, an example of munitions grade armour. This one is kinda high end of them though, with arm guards.
https://s-media-cache-ak0.pinimg.com/564x/d7/2d/f3/d72df30862b9f9ae1838d79c415d33d7.jpg
Incidentally the same kind as the Steel Fist wears.
Here's another one.
https://myarmoury.com/talk/files/harquebusier_small_583.jpg
Note the rough surface of the cuirass.