**This mark is found on the bottom of a ceramic pottery tray believed to be Japanese in origin. Any help with the interpretation will be greatly appreciated.
It seems to be 秘色窑造, 秘色窑 is a workshop making a kind of china called 秘色瓷, these four characters mean that it's made in 秘色窑.
Actually, 秘色瓷 origins in China, Yuezhou(today's Zhejiang province), in the late Tang dynasty. And it's famous for its cyan color and ice-like surface.