Oxalic Acid Rust Remover

In general, the oxalic removes fine-grained, powdery limonite or hematite deposits easily, but thick solid iron oxide crusts dissolve very slowly. Crystalline hematite patches become bright and shiny and dissolve very slowly. Oxalic acid is not good for cleaning specimens containing calcite or some other calcium minerals, as it dissolves these. Fluorite is not cleaned very well by oxalic acid and seems to be etched by it. Yellow stains can result if specimens are left in oxalic acid as it evaporates. (they should always remain completely covered by the acid.) Also, using too much baking soda to neutralize the acid can result in yellow staining.

When completely successful, oxalic acid cleaning will remove all traces of yellow-orange iron staining, for example, a specimen of clean dark smoky quartz and pure white feldspar. Many specimens, however, are too thoroughly iron-coated to achieve this goal, and the feldspar will always retain some pale red color. Yellowstained, greenish-looking amazonite becomes a clean, bluer shade after cleaning.