Vintage ✨ MISS BLACKWELL Long Sleeve Pop-Art Secretary Dress in EXCEPTIONAL Condition! Appears to be a custom couture piece. No size label. Small tag sewn in a seam appears to indicate the client name "Mary B". That was one lucky, "Mod" and stylish gal! Vintage: late 1960s-early ‘70s. It is absolutely STUNNING! Hidden back zip and hook/eye close. High neck that could be folded for a more clean line, or unfolded for a higher neck in front. Elegant cuffs with hidden snap close at end of long sleeves. Fully lined with bust darts. 6.5" slit at bottom left hem. Very slight A line. Fabric and lining is supple and soft, not slick feeling. I put this as a size 10 based on the approximate measurements shown below: APPROX MEASURE (laid flat) 15" shoulder to shoulder 19" armpit to armpit 24.5" sleeve (including cuff) 39.5" shoulder to hem 23.5" across bottom VERY RARE! I have only found one other that is similar (see last image)