The Earliest reference to the Broach’d Thurnel is recorded in Pritchards “Masonry Dissected” (1730).
In that publication, in question and answer form, the three Immovable Jewels are described. They are:- The Trasel Board, the Rough Ashler and the Broach’d Thurnel.
Their uses are:- 1. For the Master to draw designs upon. 2. For the fellow Crafts to try their Jewels upon. 3. For the Enter’d Apprentice to learn to work upon.
The Broached Thurnel was another stone.
“Broached” is an old Scottish word used among Masons signifying “to rough hew.”
“Thurnel” is the act of chipping away at, or the implement with which the chipping is carried out.
We can, therefore, understand the Broach’d Thurnel as being a stone, chipped away by a tool and used in the learning process of the Apprentice Mason.
The symbolism of the two stones is:- 1. For the skilled tradesman to examine. (The Fellow Craft was a fully qualified Operative). 2. For the Apprentice to learn upon.
It would obviously match the “two Degree” system of the days of early Speculative Masonry.
It is noted that in the English exposures of the 1760’s (when the three Degree system was in force), there were also two stones.
These were the “Rough and Smooth” Ashlars.
The Broach’d Ashler [sic] had been replaced by the Perfect Ashlar.
The symbolism has changed, and has been given a spiritual connotation.