Copper tungsten cleaning

Hi,
I am involved in plasma arc welding of PTFE coated stainless steel guidewires, .035" diameter. My problem is in cleaning the
fixturing(copper tungsten), a dark material builds up on the clamp I use(I think this is burnt PTFE or carbon or both) which is affecting weld quality.
I have tried alcohol & acetone but to no avail. Sandblasting and other abrasive techniques are not possible as it damages the precision of the fixture.
Is there any other methods I could try for this cleaning
Thanks guys, Brent.
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Electropolish
Plasma cleaning
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Harry Andreas
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