Vintage Chinese Yixing ZiSha (Purple Clay) HIGHLY Detailed Madarin Lucky Duck - Marked 21??

BEAUTIFUL super highly detailed Chinese Yixing ZiSha (Purple Clay) duck. Or is it? The feel of this clay is almost warm! Hard to tell it is even made of a lay material. SUPERB detail down to his tongue, and the teeth in his bill! EVERY pin feather is expertly wrought with what looks like a tiny pin! He is lovely to touch!

It has a 21 stamped in the bottom. His wing tip has been repaired - had to view under the loupe to see. The only air hole for firing is a TINY hole near his bottom. (He is hollow!) He is 8 inches long, 4 inches tall, 4 inches wide.

I know he's a Chinese 'Lucky Duck', probably a Mandarin duck, but is he a Yixing ZiSha duck? He is unglazed, and only his bill & one foot and the elbow of his second leg is colored. (The botto of hi is the same color as his upper body. Should I take better non-flash pics?)

Thanks in advance for your imput! ANY idea of Age/Period? NOT marked China, or made in China - only the impressed number 21.