C-60 fullerene films were reduced in aqueous solutions of potassium and sodium ions, and the effect of positively charged Bronsted acids was investigated on these reduction processes. Ammonium, hydronium (hydrogen) and hydrated aluminium ions were used as proton donors. It was established that their overall effect is different due to their different proton donating abilities. However, their primary effect can be summarized as disturbing the reduction process. Their addition shifted the reduction potential to lower values, and changed the shape of the voltammograms, but allowed the formation of nearly the same product. It is supposed that they are not inserted into the reduced films in significant amounts. That is why their effect is called a foreign ion effect. Under special conditions, however, films could be produced that probably contained aluminium ions as dopants, i.e. produced a salt of C-60 with a trivalent cation.