Fingerloop braiding is limited in complexity by the number of fingers available. In practice, this means 7 or 8 loops for a single worker. The medieval evidence suggests that it was very common for more than one person to cooperate on a braid. Excavations at London produced numerous examples of silk fingerloop braids (2nd half 12th C to first half 15th C), and 12 of the 25 were constructed from 10 or more loops (Crowfoot et al. 1992). Ten loops was most common, but there were two 20-loop braids, which would probably have required four workers. Pattern books for fingerloop braiding exist from the 15th and 17th centuries. The two 15th century examples I am familiar with contain an assortment of recipes for single and multiperson braids. (Harley: Stanley 1974, Tollemache: Griffiths 2001 (in Speiser 2000)) . These two manuscripts are partially identical, but the Tollemache manuscript describes more braids than the Harley manuscript. Although most of the braids found at London were monochrome, most of the printed recipes specify color sequences. (Note: There is at least one alternative method for working with many loops. One person works with all loops by holding them in order over the entire hand. This method may have been used extensively in Japan, but there is no evidence for its use in medieval Europe.)
The working process itself isn't much more complicated than for single person braids. Each person works their own loops, and at preset intervals the inner loops and sometimes the outer loops are exchanged. The medieval recipes strongly imply that there is a "foreman" calling out the directions as the braid proceeds. I don't see any way that some of the most complex braids could have been made without an extra person keeping track of the pattern.
Notation: For two-person braids, L is the person on the left, R is the person on the right.
Al is the index finger on the left hand, Ar the index finger on the right hand,
Bl the left middle finger, and so on. M is the middle worker for 3-person braids.
When two or more people work on the same braid, each does a set of loop manipulations, then adjacent loops are exchanged between workers. This must be done correctly to create the proper structure.
Exchanging inner loops:
L: Ar is free, Br has a loop
R: Al has a loop.
The objective is for L and R to exchange adjacent inner loops without twisting them. The 15th century solution is this:
L: Reach LAr through LBr (loop on B of the same hand) from within, and take RAl from within.
R: Take LBr onto RAl
The simplest regular one-person braids use 5 loops, and have two points where loops can be crossed or left open while working (at the outer edges), producing three possible structures (names from the Tollemache book):
Both crossed: XX (solid braid; a lace common round)
One open: X= (unfolding braid; lace piole)
Both open: == (2 braids; an open lace)
The two-person equivalents of these with 10 loops effectively have three possible crossing points, two outer and one inner, producing six possible structures. Not all appear in the medieval manuals.
Both crossed: XXX (solid braid; a thick lace bordered)
Both crossed: XX= (partly unfoldable; ?)
Both crossed: X=X (hollow braid; a hollow lace)
Both crossed: X== (unfoldable braid; ?)
Both crossed: =X= (I-beam; ?)
Both crossed: === (two braids; ?)
1. Each worker separately work the L and R loops open.
2. Exchange the inner loops as above.
3. Reverse the outmost loops on each side downward: twist the loops inward.
4. Exchange these loops in the same way as inner loops.
5. Reverse the exchanged loops upward: twist the loops outward.
This process is easiest to keep track of when using two-color loops.
Setup: Three workers, each with 5 loops of a different color. R always crosses the outer loop and leaves the inner loop open. L and M always leave both loops open.
1. M and L each exchange two loops on their own hands (do a cycle), then exchange inner loops. Repeat 4 more times, until colors are exchanged.
2. L and R work 4 cycles alone. M works 3 cycles alone.
3. M and R each do a cycle, then exchange inner loops. Repeat 4 more times, until colors are exchanged.
4. L and R work 4 cycles alone. M works 3 cycles alone.
Griffiths, Jeremy. 2001. The Tollemache Book of Secrets: A descriptive index and complete facsimile with an introduction and transcription together with Catherine Tollemache's Receipts of pastry, confectionary, etc. The Roxburghe Club, London.
Limited edition facsimile of late 15th century household book. As far as I kn ow no other edition is available. I have access to it but am not allowed to photocopy it, although I'm slowly transcribing it. The fingerloop braid recipes are available in Speiser (2000).
Speiser, Noemi. 2000. Old English pattern books for loop braiding. Self-published.
Exactly as described in the title - excellent book, but not for the faint of heart. Contains recipes from two 15th century pattern books.
Swales, Lois, and Zoe Kuhn Williams. 2000. Compleat Anachronist 108: Fingerloop Braids. The Society for Creative Anachronism, Milpitas, CA.
Covers a selection of single and multiperson braids, most transcribed from 15th century directions.
Stanley, E.G. 1974. Directions for making many sorts of laces. Pp. 89-103 in: Rowland, Beryl (ed.). Chaucer and Middle English Studies. Kent State University Press.
Transcription of the 15th century Harley pattern book. It is in Middle English, but not too hard to follow.