There are many examples of Medieval brick stitch embroidery, but I decided to use this late fourteenth century German altar hanging from the Metropolitan Museum as an example, since I managed to take good photos of it where you can clearly see the details of the silk thread.
Some of the white threads (for instance the white zig-zag pattern at the bottom of the image below) are clearly less shiny, and they also have a stronger twist than the silk. This is probably because the thread used is linen rather then silk. We know from several embroidery pieces from the same period, now in the Victoria and Albert Museum (London), that linen was often used for the white areas.
In the images below you can see a comparison of modern cotton, spun silk and filament silk embroidery floss. I used DMC cotton embroidery floss (rust brown), Soie d'Alger from Au Ver à Soie (pink) and 1200 denier from DeVere Yarns (gold).
Filament silk is made by reeling one continuous silk fiber from the silk cocoons and plying those together to form one thread. This results in very strong yarn, since one fiber is over 1 km long. After the reeling process shorter fibers stay behind. When these are combed they can be spun into yarns. This results in a less strong and less shiny and more fuzzy yarn. A more detailed description of the silk reeling process can be found here.
You will notice on these samples that the modern filament silk is much more similar to the medieval original. The reeled silk is much more shiny and less fuzzy than the cotton and spun silk threads. Here is a photo of my samples next to the original from the MET. The silk thread from DeVere has slightly more twist than the medieval silk.
The medieval embroidery appears to have been pressed, so that the individual stitches seem more flat than the ones in my sample. After pressing my own piece of embroidery, it looked even more similar. The twist of the thread is much less noticeable after this treatment.
There are different types of filament silk, depending on the thickness (expressed in 'denier' or 'nm' usually) and the amount of twist in the yarn. For medieval embroidery, both brick-stitch and needle painting types of embroidery, very loose twist filament silk was used. (If there are any exceptions to this rule, I still have to find them.) At the moment I only have experience with the silk thread from DeVere Yarns, but I will do a comparison of different brands of reeled silk soon(ish). A quick overview:
Loose twist filament silk
- basic characteristics: very strong, shiny, very even thread
- suitable for period embroidery, narrow wares, possibly less suitable for tassels
- modern option: e.g. Devere Yarns - 1200 dernier silk, Au ver a Soie - Soie Paris
- basic characteristics: less strong and shiny, not as even as filament silk
- less suitable for period embroidery, possibly suitable for tassels
- modern option: e.g. Au ver a Soie - Soie d'Alger, Aurora Silk