I might just have seen her first ever Violetta before a paying audience when she started the Opera for All tour of Traviata at High Wycombe one autumn in the 60s: with minimal cast and sets and just a piano for accompaniment, these Arts Council Tours did sterling service taking opera to places around the UK where it would never normally be seen: three separate companies, one for the South, one for the North and one for Scotland, with young singers setting out on their careers. I found the programme when I was packing to move up here a little over two years ago now. It's in storage at the moment, but I can recall that two of the other singers were Ramon Remedios (Alberto's brother) and Wyndham Parfitt.

For me Marie Collier had the edge as EM, but Barstow made an indelible impression on her first appearance as Denise in the original production of The Knot Garden, her ROH debut. 

I know exactly what you mean by that "bottled" quality, Ruth - it's a sound she's always had.

Here is a sample of Barstow for those who missed her:

http://www.youtube.com/watch?v=FLLHGFsYJ2Y&feature=related