Vintage 60s/70s Union Made Purple with white polka dots maxi dress

This is such a pretty empire waist dress with lace details. I am unsure of the material. It is fairly heavy and does not stretch. The outer laying is purple and has what looks like tiny raised cotton balls which form the mini polka dot pattern. Dress is fully lined with a sturdy smooth purple fabric. There are only 2 tags in the dress. One is the blue and white Union Label. The other is at such an odd spot on the bottom hem of the dress. It has a line for size but I really do not think any of the numbers on there correspond to a dress size. Dress has a fully metal MURLEN zipper partially down the back. A Large bow snaps over top the zipper in the back. Dress is in pretty good condition. I do notice the tips of the lace around the neck have some discoloring. Dress has not been cleaned. It does have that "hung in the closet for years" smell to it. Measurements while dress is laying flat: -Across chest 16" to 17" -Across empire waist 15.5" to 16" -Across where natural waist would be 16.5" -Across hips 22" -Length from top of shoulder to hem 54"