PE surface dulling?

[LuckyStrike]

I recently watched a video on PE (which I cannot find now), and the modeler used some kind of an acid bath to dull the finish from bright brass to a dull gray or black. It helps hide scratches and I think a bit more realistic, dark metal in lieu of brass.

I tried Ospho, which is a bare metal prep solution. It is a weak acid, but didn't work at all.

Any suggestions? Thank you in advance!

[BigWall]

Here's one type:

Photo Etch Burnishing Fluid

I've never used it so I can't vouch for it's usefullness.

[LuckyStrike]

Here's one type:

Photo Etch Burnishing Fluid

I've never used it so I can't vouch for it's usefullness.

Thanks for the info. I actually buy quite a bit from Hobbylinc. I will order some and post the results.