Melted is the past- and perfect-tense form of the verb to melt. Molten used to be the perfect-tense form, but it’s now only a past-participle adjective, and it’s mostly used in relation to molten metals and minerals. For example, while we might write the molten copper was melted yesterday, most English-speakers would write the melted ice cream melted overnight.
These trends are borne out in all modern varieties of English, including American, Australian, British, and Canadian English. As far as most major dictionaries are concerned, molten only works as an adjective.
Examples
For example, these writers use melted where writers of bygone eras may have used molten:
The piles of snow brought on by a bad winter storm a few weeks ago have melted due to unseasonably warm temperatures … [St. Louis Post-Dispatch]
The riot police have melted into the background and a number of prisoners have been released with a royal pardon. [letter to BBC News]
Place over hot, not simmering, water and stir constantly until 3/4 of the chocolate has melted. [Vancouver Sun]
And these writers use molten according to modern conventions:
Molten sulfur is used to make sulfuric acid and to bleach wood pulp for paper manufacturing. [Roanoke Times]
Indeed, the most tangible reminder of the molten metal that was the city’s lifeblood is the name of Pittsburgh’s indecently successful NFL team, the Steelers. [Independent]
The wax is then melted and drained away, leaving the mold open to be filled with molten sculpture material. [Stuff.co.nz]
