Original 1950s back midnight blue two tone shot satin dress small blue flowers detail cap sleeve rockabilly mandarin petite size
 
Oh what a stunner this is!
It has elements of a Cheongsam dress with the mandarin look collar, and cap sleeve. But then it has a lovely flare and is undauntedly a 1950s piece. Seamstress made though unlined, and unlabelled.
The iridescence of the blue in sunlight or strong night lights is unreal so breathtaking; it become a shimmering blue vision
It looks black or very midnight blue, with small blue flowers, and shot with an iridescent blue, like shot silk.
However I cannot tell what fabric this is as I managed to take a small sample from an excess interior hem and it has both synthetic and natural fibres (hard beads and papery ash; paper burn smell). So I'd say nylon and rayon, but a lovely silk satin feel and shimmer so could be silk; and likely the mix is what gives it its two tone look by mixing the warp and weft like shot silk. So anyway it is what it is, no guarantees on that but be assured its lovely though as I say part synthetic.
It is a small size, I'd say a UK4-6.  I could just get it on with a struggle being very careful with the Talon metal side zip. Though I am a UK 8 atm. Been taking sandwiches to work and I don't normally eat much carbs so gone up half a dress size this year! So if you are a UK 8 don't think about it. 4-6 would be ideal. And , while there's a four inch upturn hem, it comes to only just below knee length on me and I am 5ft 5 ins. 
So ideally you wouldn't want to be any taller than me. So this is probably going to be a dress for a petite lady or teen .
The bodice has darts to the waist which has piping and gathered before flaring. Not a full circle but quite flared, can be worn with or without petticoat. 
For the right size petite lady or teen, this is a spectacular dress which comes alive and blue in the summer sun. Ideal for the rockabilly gal who wants just a little something different and special for  summer date. And that boyfriend of yours will be working his butt off this summer to take you out in it! 
"Well, I'm a gonna raise a fuss, I'm gonna raise a holler
About workin' all summer just to try an' earn a dollar
Everytime I call my baby, to try to get a date
My boss says, no dice, son, you gotta work late
Sometimes I wonder what I'm gonna do
'Cause there ain't no cure for the summertime blues"
(Eddie Cochrane Summertime Blues 
And I can imagine this dress gleaming in the sun or a night sport in Vegas in the 1950s for sure for our hard working couples well earned vacation! So maybe some dice after all....