when nothing else will work.Restore cleans gray old sinks when nothing else works.  Always use with caution.  This product will etch some tile so always test before using.  Restore may be used on glass and mirrors when nothing else will remove the hard water and replacement is considered, then try Restore before replacing glass, but use with caution because this product may etch the glass.  Always wear gloves when using this product it penetrates when you don’t know it’s working.  Restore needs to remain on surface for approximately 60 seconds.  When cleaning tile floors always try our product X-It-Out before using restore.  Never mix these 2 products together because they will react together.