When the warlike Franks conquered the old Roman province of Gaul in the 6th century, the territory became known as France. The name originally came from the Latin franci for the javelins these fearless warriors carried. Frank, identical to the ethnic name, also meant "free, not a serf," for these barbarians were the only freemen, and reduced the Gauls to slavery.
Frank, meaning candid and outspoken, derived from the Franks' bluntness in dealing with others. From this term also comes the word "enfranchise," meaning to empower or set free.
One of the most persistent and unusual theories for this word for "pure and genuine" comes from the Latin sine cera (without wax). But why wax? In the quarries of ancient Rome, quarrymen often rubbed wax on stone slabs to cover any imperfections, and then polished them to a mirror finish. Marble and pottery dealers were also known to conceal defects in products by filling in holes and cracks with wax.
Before long, the Roman Senate caught on, and declared that all marble be "without wax," sine cera. Merchants would advertise their wares as "wax free," assuring customers that the products (and the merchants) were clean, pure, and sound.
Sources: 'The Story Behind the Words,' by Morton Freeman; 'The Encyclopedia of Word and Phrase Origins,' by Robert Hendrickson; 'The Barnhart Dictionary of Etymology,' by Robert K. Barnhart.