This is an advanced tablet weaving technique. If you are new to tablet
weaving, you might want to check out my
basic tablet weaving
page first.
These instructions are for the two-pack method, the first method I learned (from Collingwood's Techniques of Tablet Weaving. I now teach the one-pack method almost exclusively. It is slower for simple patterns or solid areas, but is easier to work with for complex patterns and provides a smoother transition to more complex techniques. There is a longer description of the one-pack method, and you may also want to read the tablet weaving theory page.

Basics
This technique has been used throughout the Middle Ages,
especially in northern Europe, to create elaborately patterned bands. The
most common designs are geometric patterns and stylized birds and
animals, but there are many possibilities. The oldest known sample comes
from Norway, and is dated to the sixth century. Other period pieces are
described in the references below.
Twill cloth has a diagonal surface structure. This means that patterns
with 45 degree diagonal lines are especially suited for this weave. All
these directions assume that you are weaving a dark colored twill with white
patterns. (The reverse side will be light with dark patterns, but the
edges of the diagonal color boundaries will not be smooth.) The cards
used for the twill weave are threaded with two light threads in adjacent
holes, and dark threads in the other two holes. The card can assume four
positions relative to the string colors.

While weaving a twill with a dark upper surface, each card moves from
position I to II to III back to I, and repeats the sequence. This
turning pattern keeps a dark thread always showing on the top. (This is
exactly like ordinary double face weave so far.) This card is out of
step with its neighbors, though, which creates the twill line in the
fabric. Twills are described as S or Z, depending on the direction of
the twill line. (This is equivalent to the use of S and Z to describe
card threading direction.)

There are two methods to weave a twill, based on the fact that an
S-threaded card turned forward is equivalent to a Z-threaded card turned
backwards as long as the color pattern is symmetric. In the one-pack
method, all cards are turned individually, and color changes are made by
reversing the turning direction. The two-pack method, which is the one
covered here (developed by Peter Collingwood), involves separating the
cards into two groups, each of which is turned as a whole. Color changes
are made by twisting the card about its vertical axis while it is in
position I or III, which interchanges the positions of the light and
dark threads, and switches the threading direction. A twist made while
the card is in position II or IV will change the threading direction
without affecting color position. Because of the frequent twisting, it
is easiest to use fairly small cards, about 5 cm.
Set-up
Several selvage cards in plain weave should be used to stabilize
the twill and provide a smooth, sturdy edge. The twill cards are
threaded two light, two dark as described above. The twill cards are
then separated alternately into two packs. The pack nearest the weaver
is composed of all the odd-numbered cards, and starts in position II.
The even-numbered cards are pushed away from the weaver, into a second
pack, which starts in position I. The selvage cards for a third pack.
There is a four-part turning sequence for the twill cards. First, both
backs are turned forward (top edge away from weaver) and the weft is
passed. Selvage pack is turned each time the twill packs are turned.
Then pack 1 is turned back (top edge toward weaver) and pack 2 is turned
forward. Both packs are turned back, and finally pack 1 is turned
forward and pack 2 is turned back. If the selvage pack is always turned
forward, the outermost card can be labeled in such a way that the top
edge always indicates the current turning pattern.

The threading direction of the cards depends on the desired twill
direction. Examples of both S and Z twills are shown below. Twill
direction can be changed while weaving by twisting cards in position II.
Pattern drafting
While it seems complicated at first, designing patterns actually follows
a few straightforward rules. It is impossible to crate a smooth line
across the width of the band, but lines along the band and at 45 degree angles
are possible. Color changes can only occur when a card is in position I
or III. This means that a color change must be a multiple of two turns
long, and that cards in different packs cannot change colors at the same
time. Graph paper can be used to design patterns, although I use
"rectangle paper," which conforms to the limitations of this technique.
This type of paper is available in craft stores for designing bead loom
patterns, and I have put a
sample piece online.
The underlying principle is that a card in position I relative to the
top color at a color change must be treaded in the same direction as the
line of the color change, and a card in position III must be threaded in
the opposite direction. If a card is threaded in the wrong direction for
a smooth color change, twisting it while it is in position II just
before the interchange will put the card in the right orientation
without leaving long floats. While learning how this rule translates
into practice, I found it helpful to draw out the threading direction
and card position at each color change. There are some derived rules
which can also be useful. If two parallel diagonal color boundaries are
2, 6, 10, etc. turns apart, no twists are needed to adjust threading
direction. If two perpendicular boundaries are 4, 8, 12, etc. turns
apart, no twists are needed.
Steps in drafting a pattern.
- Draw the design on graph paper, remembering that color boundaries
must be separated by multiples of two turns.
- Determine whether the card is in position I or III at each color change
(with an arbitrary starting point.)
- Decide what the twill direction for each section of the pattern
should be (your call) and use that information to determine the proper
threading direction for each card at each color change.
- Use the threading directions to determine both the initial set-up
and the locations where a twist is required.

A Few Twill References
Collingwood, Peter. 1982. The Techniques of Tablet Weaving.
Watson-Guptill Publications, New York. This is the only source I know of
for the 2-pack method of weaving 3/1 broken twill.
Crowfoot, Grace M. 1939. The tablet-woven braids from the vestments of
St. Cuthbert at Durham. Antiquaries Journal 19: 57-80. Alternative method
of weaving twill is described briefly.
Henshall, Audrey. 1964. Five tablet-woven seal tags. Archaeological
Journal 121: 154-162.
See also Table 2 in TW structure and theory for a more comprehensive list of references.
