The “terrine triangulaire” can be found on first and third degree tracing boards in Le Parfait Maçon, 1744.
It appears that the bowl is used for lighting the room:
The place where they gather, which is called the Lodge, must be lit only by a large triangular bowl filled with wine spirit, or other combustible substances, which are set on fire, and which are carefully renewed.
Elsewhere in the same book it says that:
As this is presented to the public as the legendary masterpiece of Masonry, in order to put him in a position not to miss anything of all its beauties, the fire in the triangular bowl is extinguished, and a large number of lighted candles are placed on it, representing, it is said, the 10,000 candlesticks that Solomon had made to light the temple to light the temple. Once this was done, the master took the trouble the trouble of giving the instruction shortly, as he fled.
1st degree tracing board. Frequently reproduced. Can be found in Feddersen (Die Arbeitstafel in der Freimaurerei Band I (1982) F/34, P. 304). It comes from Le Parfait Mácon 1744.