Wow, I must say that I find you very couragious!
I am a graduate fine jeweller and I am not even doing experiments
like these with the finer metals.
In my studies I learnt to respect the precious metals. Learning that
you had sterling flush over the gold makes my eyes crossed.
You need separated tools to work in Platinum and everything around
the workarea must be cleaned. You will destroy your files if you
were thinking of using your normal tools. Platinum has such a high
melting temperature and slightest dust will melt into the metal and
make pores. That is not considered acceptable when you have Platinum
in your hands.
Be safe and hire a professional!