My experiment on how to chemically remove mill scale ...the cleanest way.

**Claudio HG** · Apr 24, 2021, 06:55 AM

Hello everybody, in this video I ventured into chemistry. My goal was to remove the mill scale that cover mild steel having care to deal with the resulting spent liquor. In this video I addressed all that. Hope you'll find it interesting. Cheers.

**batchit** · Apr 27, 2021, 09:07 PM

I use Hydrochloric Acid and Hydrogen Peroxide mix to etch my homemade pcb's. Also when using Hydrochloric Acid in an open container the fumes will travel everywhere and attack any unprotected metal within cooee.

**Claudio HG** · Apr 28, 2021, 02:20 AM

LOL I had to search in Wikipedia for "within cooee". Nice. Yes HCl acid is pretty aggressive, that's why I suggested to stay outdoor, or at least have a good ventilation with a fan to extract fumes. But it also depends by the concentration of the acid. 33% does release fumes but way less than higher concentrations (say 66% which is pretty harder to manage). When etching PCBs I use an even lower concentration at 8.5%, with 5% of H2O2, working at 40°C.
Also the rate of fumes released is dependent on the exposed surface: the narrower the vessel that contains the acid the less fumes are released. Often people (including me) use a large tray to etch PCBs making easier for the acid to release fumes. A better solution would be to use a narrow (a two, three centimeters) and tall container, and to place the board to be etched vertically.