The thing about buying vintage is that you get a slice of history with each purchase. In this case it's the trademark Orlon/Antron trademark synthetic fabrics it's made from. Orlon acrylic and Antron nylon were the space age fabrics manufactured by DuPont. These ready to wear designs made from the new fabrics were more durable, washable and easy to wear as well as looking great. These new age fabric inventions landed at the same time as the Apollo space mission - in fact, Du Pont played a part in the manufacture of Neil Armstrong's suit!
Enough of the history lesson. 
You now know that apart from looking and feeling good, this dress has survived the decades so well thanks to it's fabulous fibres.
The seventies look can be seen in the larger pointed collars and that front zipper with it's feature binding. Long sleeved the dress reaches the knees and is unlined - the inside is as cosy as it gets.
I would describe the diamond patterned colours as deep purple and silver white.

Underarm to underarm 18.5" / 47cm approx 37" / 94cm chest
Shoulder to shoulder 15.5" / 39cm
Shoulder to cuff 20.5" / 52.5cm
Underarm 15.5" / 39.5cm
Collar length front 4.5" / 11.5cm
Waist across 17" / 43cm approx 35" / 86cm waist
Hip across 19" / 48cm approx 38" / 96cm hips
Back of neck to hem 38" / 96.5cm

There is a small degree of stretch across.

This dress is in excellent condition for its age and looks as stylisht now as it did fifty years ago.

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Vintage 70's St Michael Long Sleeved Dress sz16