I also use a butane micro torch which has a smaller flame for more control. One thing about copper is that it conducts heat much better than steel, so it is difficult to keep the colors where you want. Practice on some scraps before attacking a finished piece. As a last resort you can drop a piece in the pickling solution ( I use vinegar) to clean off the oxides and start over.
As Thomas reports, a coating of clear lacquer or wax will steal some of the color from your piece, but sometimes it is necessary if it will be handled. Oh well, nothing is forever. Have fun with it.