Received from Dave at 3/24/2019 02:25 AM UTC:
I have a bottle of FeCI from RatShack I bought 15 years or more ago still unopened. Read all kinds of stories about that stuff. Being I am a noob just starting I read all the comments and I may try different methods so this is just another note in my toolbox.
I don't like ferric chloride (FeCl3) because the solution is too dark to observe the progress of the etching and it doesn't change color appreciably as it becomes spent so you don't know it's spent until it doesn't work. That and it makes for stains that are very hard to remove.
That said, if none of that bothers you, it works just fine for etching copper and it can be rejuvenated by bubbling air thru it. Etch and rejuvenate enough and you'll need to add a bit of HCl too. I guess you'll know when adding a bit of HCl is necessary when it won't etch copper properly even after extensive rejuvenation. The color of the solution prevents seeing when it isn't properly rejuvenated so you can't tell when to add HCl until you're disappointed in the results.
I see people saying ferric chloride is "sludgy." If it's sludgy it's probably badly spent and/or overconcentrated from repeated use and repeated rejuvenation. sludgy solution just needs rejuvenating with bubbled air (or H2O2) and probably a bit of HCl also. And some water if too heavily loaded with copper. Properly maintained solution won't be sludgy. The thing is... at this point you're also etching with the cupric chloride the solution also contains... so just start out with cupric chloride and have a solution that's nicer to work with and easier to see if it needs rejuvenation.
Jim H
