heat treating engraved steel ?

[SVanderkolff]

We are in the process of making a fully engraved lockback folder of 440C. The blade, backspine, butt spacer have all been engraved and now successfully heat treated. They have just come out of the tempering oven and look great. They all, though, do have that patins of grey on them from the vaccuum heat treat. What is the best way to get rid of that patina. Should I sand with 1200 grit paper, lightly buff with white or green rouge? Your help would be greatly appreciated.
Thanks
Steve

 

[Hengelo_77]

Wouldn't vinegar eat off the HT skin?
Or maybe a stronger acid like a goldsmith pickeling.