You should correct the amount of H2O...I think 985 ml are too much!

> This is what I used to etch Cr.  It should be safe with oxide.  You need
> to check if it is OK with PMMA.  There are also commercial etchants you
> can buy.
>
> Nichrome Etch: 155 g (NHb4)2Ce(NO3)6  (Ceric Ammonium Nitrate) + 60 ml
> HNO3 + 985 ml H2O