Just wondering if thats a mineral or an oxide formation? Muriatic acid in a coffee cup to a five gallon bucket used to work as a ratio acid/water mix. Mabe a quart of acid to a full tank would work. It really does a job on oxides (RUST) or minerals like calcium salts. However the time you leave it in should be only about 15 minutes, as it can eat through any rust spot 'pinholes' waiting to happen. I used it a couple years back to clean Bultaco bolts. Bultaco being a vintage Spanish racing bike from the 60's through the 80's. Bultacos had allen bolts throughout with 'BULTACO' stamped in the bolts, making them very desireable for restorers rather than store bought bolts w/no stamping, but often times age had rusted the bolts enough that they looked pretty ratty, especially when doing a full resto. My solution...... Initally was to soak them in a small bowl with a 25% solution of water/muriatic acid for what usually was about anywhere from 15 minuates to an hour if they were really trashed. This gave me a 'as new' appearance to the bolts with all of the corrosion removed. Then I would put them in another bowl in my sink with running cold watter to rinse them for a couple minutes, then spray with WD40 to protect from flash rust. then to remove that before painting the nuts, a bath of acitone to remove the WD. Point is, after this long winded storie, that muriatic acid will remove and etch clean steel like nobodys business. CAUTION !! Muriatic acid does NOT work with ALUMINUM as it causes a furrious reaction and turns aluminum black and actually eats it up in short order, I mean parts will dissapear.......yea really...!!
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