Oxalic acid removes ferric chloride stains. I've got a big bottle of it somewhere but have never used it.
Leon
On Monday, 3 July 2017, 2:56, "'Brad' unclefalter@... [Homebrew_PCBs]" <Homebrew_PCBs@yahoogroups.com> wrote:
I have been using ferric to etch boards for a while now. Recently I got lucky and came into a cache of 1973 vintage copper clad PCB stock, which will enable me to make some reproduction pieces that are pretty much indistinguishable from originals in terms of look. However, I have noticed that the ferric solution stains these boards, adding a yellowish tint. Is there any way to avoid this? Or clean it after?