Normally I don't care about rust stains on my rocks. You can avoid them, after all, with careful collecting and trimming of hand specimens. But before I submitted a group of gneiss specimens to a local learning center, I decided to remove the brown and reveal the details. For that, the default treatment is oxalic acid. This new demonstration takes you through the process and shows the results. Oxalic acid is poisonous, but with care, amateurs can do this safely at home.
Before and after oxalic acid cleaning Geology Guide photos