the present invention relates to compositions , kits and processes for the brightening of metal surfaces by the application of the chemical compositions . these compositions act to release hydrofluoric acid as a brightening agent . the solutions are preferably mixed during application of the brightening composition to a metal surface by mixing the solutions immediately prior to or even during application of the solution . this can be readily accomplished by mixing two solutions , one having a fluoride source and the other having a strong acid to release hydrofluoric acid from the fluoride source , the mixing occurring immediately before spray application , during spraying , or immediately after spraying of the two solutions . mixing may be done on - site , which means that mixing is performed at the site of use , usually on the same day of use or even within a few minutes of use . optional , longer term mixing may be performed , even over night or over the weekend , but actual solutions of hydrofluoric acid do not have to be shipped to the site .