What is a good macro etch for laser welds on copper?

Is ferric chloride in water - HCl best?  We have tried a few different acid mixes with less than desired results.

What is the ASTM suggestion?  I think we have tried 50-50 Nitric and HCl in water but it is still too gentle.

What about straight undiluted acid on the weld?  This one is dangerous I think. And, it might just turn black.