Lunn tunic/vest, black. No size

This is a lovely vintage Lunn tunic or vest. It can be worn open or closed layered over a variety of other pieces. I love the sweet squared neckline. It has two huge pockets. I’ve had this in my closet for over 20 years! But it is still in great shape. Slightly faded from wear/washing. 50% cotton and 50% linen. There is no size on the label. The dress form has a 39in bust. The tunic has an elastic back. From the underarm it measures 22inches. Prob a size M or 8