Guess the secret ingredient

A little picture,two inches by three inches,bought at a boy scouts' jumble sale more than fifty years ago. And a pair of iridescent blue cufflinks,picked up in a charity shop years ago to wear with a denim shirt.
Pretty things,but .....
..... vintage items made from butterfly wings.

I wouldn't buy them now,but I was quite young when I bought the picture. I was enchanted by the way it would change from a daytime scene to a night-time one depending on how the light caught it,and it only cost threepence. It's stood on my dressing-table ever since,the colours as bright as the day I first saw it.
I believe butterfly wing jewellery was popular between the wars,but I'm glad it's a fashion that won't come back.