Wrap the copper in Denso tape. Then line the channel with dpm. Screed over that, but use some cement dye to colour the infill. That way it will be easier to identify the pipe run.
If using 15mm copper, the Denso can be unrolled along the pipe length and moulded around the pipe. Definitely wear...
Stanley knife or a sharp scraper will take care of most, if not all of it.
The silicone eater described above really only works best on thin layers of silicone
What you may have might not be silicone, but Acrylic frame sealant. Only scraping will get that off..
The whole fake patina thing just looks so tacky. It doesn't really work over here as we never had the climate to produce it. The most we get is a red car faded to pink...
Best just paint it normally , but go for something 2 tone
You might even get away with an A Team setup....
The Bergen branded guns off of ebay are pretty good too. I have the mini gravity 0.8 setup one, and have used the bigger 1.3 setup one, which will be added to the arsenal...