Brickkiln - Possibly, a pavement of brick. Jeremiah was to take a few large stones, such, nevertheless, as he could carry in his hand, and build with them, in the propylaea before the royal palace, something that would serve to represent the dais upon which the seat of kings was usually placed. By hiding them in the clay is meant plastering them over with mortar.
Related Commentaries of Jeremiah 43:9
Jeremiah 43:9
9 Take great stones in thine hand, and hide them in the clay in the brickkiln, which is at the entry of Pharaoh's house in Tahpanhes, in the sight of the men of Judah;