The derivation of the word sincerely
actually dates back to ancient times
and the practice of making sculpture
. It was not uncommon for the marble
to be chipped
while it was being sculpted, and in order to make the form perfect, hot wax
was poured into the crevices to fill them up. When the surface was polished, the wax became indistinguishable from the rest of the marble and the sculpture appeared to be perfect.
For all intents and purposes, the solution was unnoticeable unless people placed the sculpture outside or in a garden. The sun would melt the wax, and the flaws would be revealed. People were furious that they were paying so much money for statues which turned out to be flawed. They demanded that they be sold only true, flawless works of art. This led to vendors advertising their wares as being without wax, or in the language of the time, sine cere. In the same vein*, if a person is not hiding anything or covering up the truth, they are considered to be sincere.
*Ha! A marble joke! I kill me!