Many modern people think that clothes in the Middle Ages were drab, grey-brown things. Archaeological finds of clothing or textiles, rare as they are, often seem to support this: they all look brown.

This brown-ness is deceptive, though. Medieval people enjoyed colours, and dyeing textiles has been done since at least the Bronze Age. Modern methods are getting better and better at detecting colouring substances from plants and animals in medieval textile finds, too.

So we do know for sure that medieval fabrics, including those used for garments, were dyed. Literary sources indicate that bright, clear colours were most highly prized . These colours are easiest to achieve on animal fibres such as wool and silk, while linen can be very hard to dye in a bright, saturated colour. On wool, however, a huge spectrum of colours can be dyed.

The typical dyeing procedure used for most plant- or insect-based dyes consists of two steps: mordanting and dyeing. During mordanting, the textile is treated with metal salts such as alum (which contains aluminium). The metal salts bind themselves to the fibres; during the next step, the dyeing step, the colouring substances from the plants in turn bind to the metal.

Alum was the most common mordant, as it helps produce clear and bright colours. Mordanting with iron, for example, typically results in murkier shades that shift towards green or brown tones. Reseda luteola (dyer’s weld) will only produce a clear yellow on alum, while on an iron mordant, it will dye a shade of olive-green.

This is also true for other plants that produce other shades. Apart from the mordanting agent, many other factors can influence the outcome of the dyeing: water quality and water impurities, other additives, concentration of the colourant in the plant, heat and duration of the dyeing process, even the material that the dyeing pots are made of can have an impact on what shade will be the end result. This also means that even if we are able to identify the plant used to dye an archaeological textile find, we still don’t know what colour it was. We only know the colour range it may have belonged to, and that range can be quite wide. Most plants that yield a yellow colour can be used to dye yellow ranging into green and brown shades down to a deep brown, for instance; reds can range from pink or orange hues to reddish-browns or almost black colours.

Are you wondering why blue was not mentioned yet? There is only one plant native to Europe that will yield a blue dye, and that is Isatis tinctoria – dyer’s woad. The woad plant needs special handling, though. Its colourant, indigo, is not a mordant dye but a vat dye. It needs to undergo a chemical reduction before it can bind to the fibre, turning it from blue into a yellowish-green substance. Once the textile is pulled out of the dye bath, the oxygen in the air reacts with the dyestuff, turning it blue almost instantly. Several cycles of immersion and oxydation will result in a deeper, darker blue, while just one or two dips result in a lighter shade. Woad, being a vat dye, will also work nicely on linen, hemp or other plant fibres, as opposed to most mordant dyes.

Woad blue, dyed on top of naturally brown sheep’s wool, will also result in a spectacular shade of black with a blueish sheen. Dyed on top of yellow, woad will change it into the most vivid and brilliant green, clearer in hue than the greens achieved with single-plant mordanting dyes. And finally, if used in combination with madder (Rubia tinctorum), the prime plant for red dye, it can even be used to fake purple. True purple, derived from a mollusc caught in the Mediterranean, was only accessible for the super-rich, as hundreds or even thousands of these sea snails are necessary to produce enough dye for even a bit of cloth. More affordable, but still quite expensive, were the insect dyes kermes and cochenille, both used for shades of red – cochenille more towards the pink hues, kermes more towards true red shades.

The range of colours available for the wealthy was thus almost unlimited. Literary texts speak of grass-green, sky-blue, blood-red and coal-black textiles. From light hues to bright saturated colours to subdued tones, dyed on top of naturally coloured wools, something to add a splash of colour would have been available to suit every purse. When we imagine how people in the Middle Ages dressed themselves or decorated their home with blankets, cushions and other domestic textiles, we should thus replace the drab and brown hues before our mind’s eye with colours from light and bright to subdued… but definitely full of colour.

Information Source: https://thehistoryvault.co.uk/medieval-textiles/