Is it safe to use an acid to clean a flamed finish granite?

All acids should be used with caution on any stone surfaces. Granite is one stone type where most acids will not harm it. However, stay away from hydrochloric acid (HCL). HCL can deposit salts in the granites pores if not rinsed throughly. I would suggest purchasing an acid based cleaner specifically designed for granite surfaces. If you have trouble finding them you may want to try sulfamic acid. Sulfamic acid is a relatively odorless acid that is used for cleaning grout on tile surfaces. As always and when working with any chemicals, read the material safety data sheet and heed all safety precautions.

TIP There are also several acid cleaners manufactured specifically for unpolished granite surfaces. Check with the suppliers in the resource directory.