In the Greek original of the New Testament the word used means 'judged in the sunlight'; and the English word is derived from the Latin—'sine cera', which means 'without wax'. In the days when art flourished in ancient Greece, it was the common practice to repair with 'invisible' wax any vase or statue that had, as a result of carelessness or misadventure, been damaged.
A rich man or a person of high rank might employ a sculptor to chisel his bust in marble. Sometimes, if the chisel slipped, the end of the nose would be chipped off. Rather than go to all the trouble of making a new bust, the sculptor would so mend the features with wax that the flaw could not be detected unless by very close scrutiny, and palm off on the customer his defective workmanship. If the client happened to be a knowing person, he would carry the finished statuette out of the studio into the open before paying for it, and examine it carefully in the sunlight: otherwise, in course of time, he would have the chagrin of seeing the nose drop off his statuette in the heated room of his house. The statue was not `sincere', not 'without wax', and could not bear careful scrutiny in the sunlight.
(Josh. 24. 14; 2 Cor. 2. 17; Phil. 1. 10)