Etymological Fables

Today I came across a word history of sincere that seems impossible. According to the story, Latin potters would sometimes use wax to conceal cracks in their products. Vendors in the marketplace, knowing that the buyers were wary of this ruse, would praise their wares as sin cera--without wax.

(Are there any valid etymologies that end with ". . . so people used to say ________"?)

The author of this word history intended to illustrate that sincerity requires allowing the cracks to show. A good point to make, especially in a church context, where there is great pressure to conceal our weaknesses. Somehow this etymological fable is less offensive to my sensibilities because the point isn't really the etymology. One can think of it as an elaborate pun, a just-so story, rather than a statement about the origin of sincere.

But what is the true etymon of sincere? Merriam-Webster's tentatively traces it to "sem- one + -cerus (akin to Latin crescere to grow)." The New Century Dictionary follows a similar line, associating the initial syllable with the sim- in Latin simplex. The OED concurs and explicitly puts down those Latin pottery merchants: "There is no probability in the old explanation from sine cera ‘without wax’."

It's disappointing that only Merriam-Webster's ventures a guess at the second half of the word. If the "without wax" story is well-known enough for the OED to knock it down, there must be some vigorous discussion somewhere of what that second element is. I submit the question to Professor Liberman and his legendary database.

And while he's pondering wax, perhaps he'd care to comment on the relationship between the English noun wax and the verb wax. According to the OED, "it seems not impossible" that the two share a common etymon (wax being "that which grows (in the honeycomb)"), but "the view now most in favour refers the word to the Indogermanic root *weg- to weave." Merriam-Webster's etymology of sincere seems to imply that the Latin words for wax (the noun) and grow share a common origin.