Making magnesium oil with magnesium flakes is a bad idea. The flakes are produced by high temperature processing which creates hydrochloric acid, which is harmful to the kidneys. All to save a few dollars and pretend to be DIY. Prefer transdermal magnesium oil with the Zechstein Inside® trademark in GLASS bottles or you will be getting a chemically treated, low grade, USP, generic magnesium which will affect over 800 processes in the human body and can be done right for only 50 bucks a year. Dont be cheap on this essential mineral. Flakes may improve the horrible USA bath water systems and in this sense they are good. But superficial bath detoxing in endocrine disruptor and possibly radioactive element infested waters is a bad idea when it comes to optimizing quality molecular magnesium at the cellular level.