I posted this photo on the weekend which shows the vibrant blue found on the original sampler. It is quite amazing that the colour is so strong centuries (1656 !!) after it was dyed.

The dye most probably used was woad.

Since ancient times, woad was an important source of blue dye and was cultivated throughout Europe, especially in Western and Southern Europe. 

Woad was one of the three staples of the European dyeing industry, along with weld (yellow) and madder (red

Woad has a long association with East Anglia, the land of the Iceni tribe and of its famous leader Boudicca. The plant whose deep blue pigment was used as a warpaint by the ancient Britons to frighten their enemies

Woad was not used only for textile dyes and, for example the illustrators of the Lindisfarne Gospels (late 7th/early 8th century) used a woad-based pigment for the blue.

In medieval times there were important woad-growing regions in England, Germany and France. Towns such as Toulouse became prosperous from the woad trade. 

The blue threads in the Bayeux Tapestry were dyed using woad and the blue in the tapestry is the only colour not to have faded in more than 900 years. 

In England woad cultivation became strictly regulated in the late 1500s in a period of food shortage leading up to the famine of 1586 and concerns that too much land was being devoted to woad rather than to cereals. Queen Elizabeth I issued a “Proclamation against the sowing of woade” on 14 October 1585

The dye chemical extracted from woad is indigo, the same dye extracted from “true indigo”, Indigofera tinctoria, but in a lower concentration. 

When woad leaves are harvested, in July and September, they are washed and heated in hot water for several minutes. The blueish water is then mixed with chalk and left to settle. A blue paste is left after the water is poured off and this, when dry, can be ground into a fine powder to be used in paints, dyes and ink-making.

Clothes dyed with woad indigo at first appear yellow, but as they dry they turn green, then turquoise then finally deep blue.

Although woad has not been grown in the UK commercially since the 16th century, it was produced in Lincolnshire during the 1920s and 1930s to provide dye for Royal Air Force uniforms, before the adoption of synthetic colourings.