- During the acid etching process, mat-bright to mirror-bright surfaces develop. For the electrolytical brightening Alfiflex 490 is used. The chemical brightening can be effected with nitric acid, if mirror-bright surfaces are desired, and without nitric acid, if mat-bright surfaces are desired. The appropriate products are Alfiflex 403 (with nitric acid) and Alfiflex 450 (without nitric acid). Further environmentally friendly modifications are available.