The Stamp Advisory Committee compared the essays of Machin's simplified 'Coinage Head' with those of the Hedgecoe photographs. They preferred the simple style of Machin's work, but suggested that the diadem replace the tiara. This was a clear echo of the Penny Black, which had influenced Machin throughout.

Machin created a new plaster cast incorporating the diadem – the 'Diadem Head' – in October 1966. A diadem is a completely circular head ornament. This example was made in 1820 by Rundell, Bridge & Rundell, silversmiths to the King, for the coronation of King George IV.

It is set with 1,333 diamonds with a pearl base. The national emblems of the rose, thistle and shamrock alternate with crosses patée. Although it was originally designed for King George IV to be worn outside a velvet Cap of State, it has been more frequently worn by queens.

It appears worn by Queen Victoria (without the Cap) on the Penny Black and all of her subsequent stamps. The Wilding definitives also showed Queen Elizabeth wearing it, and today, the diadem is worn by The Queen when travelling to and from the State Opening of Parliament.

Machin's 'Diadem Head' was now much closer to the final icon we know today. This was photographed under different lighting conditions and trial stamps were printed.

As soon as the 'Diadem Head' essays were produced they were described as a vast improvement. However, Machin wanted to 'retouch' the model to eliminate the sharp cut at the shoulder.

Working on photographs he sketched a corsage (clothing) and produced another plaster cast called the 'Dressed Head'. When a selection of essays was shown to The Queen in January 1967 she preferred this head to all previously proposed.

Machin was anxious to preserve the relief effect in the photograph of the final sculpture. To do this he thought sombre colours were important. He recalled:

"We had endless discussions about colour. The guiding principle was to find colours that wouldn't minimise the relief effect and blur the details. Colour without form, which seems to intrigue many people these days, in itself has no meaning for me. Patches of colours, areas of colour – all this I find extremely boring and elementary.
Colours can be rich and give a sense of brightness without being garish."

A long series of colour trials took place from December 1966 till February 1967. Both solid and gradated pastel backgrounds were also tried, as well as some metallic colours. The final selection included pastel and solid backgrounds, some bicoloured.

The Queen chose a particular colour (olive brown sepia) for the inland letter rate stamp, deliberately harking back to the Penny Black. This kept within Machin's scheme for maintaining the relief effect.

The final stamps were issued in sections from 5 June 1967. It was a design which would remain essentially unchanged for more than forty years.

Illustrations

Final photo of the Machin head

Machin's new plaster cast with diadem

"Dressed Head based on "Diadem Head"

Plaster mould for final Dressed Head

First day cover signed by Arnold Machin