MM Oxalic Acid (Wood Bleach & Rust Remover)

Step up in toxicity from the other acids covered so far (vinegar, citric, cream of tartar) — oxalic acid is genuinely poisonous if ingested and needs to be handled with real respect, not just the routine caution given to milder kitchen acids. It earns its place in the MM system because nothing else touches rust stains and gray, weathered wood the way it does.