These baskets are made by stitching around a wad of material that is constantly being added to. This addition is to maintain an even coil. The basket starts with the base and then pushing the coils upwards creates the sides. The basket is actually a very elaborate spiral. The coil of basic material is stitched to the previous coil using willow or bramble skein, or twined rush, marram grass or bought twine
The core material is uncovered. Traditions elsewhere in the world sometimes cover the central core material with another one such as some kind of leaf like rush.
In our searches we have found Scottish coiled baskets made with sea bent grass/bent grass/marram grass, oat straw, and rush which is probably Juncus effuses whose common names are Soft Rush, Field Rush or, in Shetland, Floss.
See also Alisdair Davidson’s recreations of ancient coiled baskets here
These photos of Jimmy Work were taken by Pip Weaser at the Scottish Basketmakers Autumn Gathering course in 2007.