What happens when injecting lemon juice and salt with a tattoo machine on an existing tattoo?

You should absolutely not do this. The ink is imbedded in the dermis and comprised of extremely dense carbon particles with various pigments and other substances. There is no way a little lemon juice will break up the ink. At the very least this will be very painful.  Worst case scenarios are that doing this could lead to infection and scarring. There are really only two options for tattoo removal, excision and laser. Please see a professional with experience and do not try this dangerous homemade concoction.

Hello and thank you for asking your question about this.  I absolutely concur with my colleague that this is a potentially very dangerous way to attempt tattoo removal and will not yield any positive results, for the scientific and clinical reasons that she gave.  Please do not attempt this, you will be putting yourself at serious risk.  Tattoo removal should only be attempted in a clinical setting, please see an expert in the medical field.