Lemishine is predominately citric acid. Acid is corrosive. Acid also exposes bare metal.

If you clean brass with Lemishine or citric acid, you have to be sure to rinse every trace of it off your brass, and keep it in an inert enviroment, or coat it with some kind of preservative. If you don't, your nice clean shiny brass will almost immediately begin to tarnish or corrode again.