In lacemaking, gimp threads are used to outline areas of the design, to define and highlight them. The gimp is usually a slightly thicker thread than that used in the main body of the lace or it can be made up from a bunch of threads used together to make a thicker outline as you can see in the detail below.
In bobbin lacemaking the gimp is incorporated into the lace as the work progresses and you can see below how the threads are kept in place by twisting the bobbin threads either side of it.
Once the gimp thread has been worked around a circular shape for example it is overlapped for a small section, secured by twisted threads moving into the body of the lace and then cut off close to the work. In early machine-made lace the gimp was often added after the remainder of the lace had been made. This work was done by women couching the thicker thread on the surface of the lace around the main elements of the design. In later machine-made lace the gimp was incorporated into the work but for areas of lace where the gimp was not required the gimp thread was ‘floated’ behind the work without being incorporated into the lace and these floating threads were later trimmed by hand.
It seems a lot of work to add these additional threads but you only have to look at the reverse of a piece of lace (lower image) to see how the flat work is lifted by the addition of a slightly raised outlining thread on the surface in the image above.