What are good ways to clean up black stuff & staining from powder coated mild steel items & bolts/ screws, after DIY mods at a Lathe heavy metal workshop?

Anything anyone touches without washing their hands has black stains all over.

This is the only industrial workshop I have access to via a connection. I got some drilling & threading done. The workers hands are all black due to tons of lathe work being done there; mix of lubes, etc whatever applies to the lathing, drilling, threading, and other metal work of this sort. They never clean the parts as they are meant to go into industrial spaces. At most they do something called blackening before shipping it off.

No one gave me any inputs on how to clean these, so I do not know what chemical or solvent or liquid to use to wash these off the formerly clean surfaces. Surely I can't use soap & water? One fellow there said Collin spray (blue colored home use type of glass & multi purpose spray).

I will need to go there again for a few more and will come back with stained metal parts & bolts again.

I am in Asia, but US / UK Suggestions are welcome as long as I can source the product or translate that and its active chemical ingredient and find a local clone.