there is a virtually identically shaped piece - with similar sommerso amber and red colours - in Andy McConnell's 'Miller's 20th-Century Glass' - page 86. Under the heading of 'Twentieth-century Murano Glass', the piece is described as a 'cut object, 1970s or 80s sommerso' - unfortunately, the description doesn't include the size, but the impression is that your piece and the book example are probably fairly similar in proportions.