Matte Green Arts and Crafts Pottery Vase with Recessed Sides

There's no mark on the base of this American Arts and Crafts pottery vase and I haven't been able to find another with same form to match it to. My gut tells me it might be Hampshire pottery but I can't say for sure. In any case, its three concave sides make for a great sculptural form, and though the glaze shows some age and wear, it's exactly the super rich matte green that makes Arts and Crafts pottery my favorite. 

6 3/8" t x 4 3/4 w. No chips or cracks or other structural issues. The glaze shows some variation due I believe to age, and there are some surface scuffs and stains, including what looks like a few pencil and pen marks--but still really a lovely piece.