One of the rarest Welsh clocks ever to reach the market will go under the hammer at Bonhams' Chester saleroom on November 5.
It is estimated to sell for £7,000 to £10,000.
John Owen, founder of the prolific Llanrwst dynasty of clockmakers, made the exceptional long case timepiece for his landlord Peter Titley, around 1772.
Titley, a doctor, apothecary and surgeon, is thought to have commissioned it - alongside a canteen of silver cutlery hallmarked with that date - as a status symbol adequately reflecting his social aspirations and growing estate around the Conwy Valley town in Wales, UK.
The clock case was ordered in the finest solid Cuban mahogany - then still little-known outside the fashionable drawing rooms of the metropolis - and the wood specially carted from Liverpool or Chester.
The dial plate, weighing a huge 9.5lbs, is completely silvered and finely engraved by "the Good Engraver" with the coat of arms of the thirteenth Noble Tribe of Wales.
"Titley probably wished to suggest a link back to the 11th Century tribe of Ednywain Bendew, 'the strong skulled' Lord of Tegaingle" said Bonhams clock specialist, Mark Huddleston.
"I think Titley was undoubtedly making a statement- setting himself apart with a clock superior to all the other Owen oak-cased and brass faced clocks in the valley."
Certainly the Titley clock, now estimated between £7,000- £10,000 and being sold by a Lancashire descendent, seems to be the only one known to boast that heraldic bearing.
"This clock is very special its own right for so many reasons- a piece of museum quality which we believe will attract the interest of collectors and academics from a wide area," said Mr. Huddleston.
"But a reliable provenance from the time it was sold to the present day is the icing on the cake. We know the clockmaker, his customer, and exactly where the clock has been since the day it left Owen's workshop."
Other features that make the clock so remarkable is that its movement included a centre seconds hand and a maintaining mechanism which allowed it to be wound without stopping and losing time.
Although, on this occasion, Owen's casemaker worked in Cuban mahogany instead of oak, he used a pattern which is unmistakably identical to other clocks produced by the Llanrwst master.
"John Owen probably made hundreds of clocks during his lifetime but only one quite like this. It was his crowning glory," said Anthony Bennett, Bonhams Regional Director.
"It is without doubt an important part of the history of horology in the Principality and we will be delighted if its connection with Wales can be maintained."
John Owen died in 1776, in his late fifties, and it is likely that in addition to being his most interesting and unusual work, the Titley clock may also have been among the last to leave his Denbigh Street workshop.