Advanced Sprang Techniques
THL Eva vanOldebroek
This course assumes you already have some experience with basic Z-twist sprang. Instructions for warping and to get started can be found here: http://mktag.org/ , the Guild of Withie and Woolmongers site. Look under “Projects” for the basic sprang tutorial by THL Cassandra of Glastonbury.
The two basic manipulations in sprang are the Z- and the S- twist. Z-twist is made by bringing the back thread up to the right if the front thread (The red thread represents the back thread). To twist two front or back threads together, the left-hand thread is moved under the right and to the front.
S-twist is made by bringing the back thread to the left of the front thread. To twist two front or two back threads together, the right-hand thread is brought under the left and to the front.
These two movements will get you through most of the patterns.
Examples of this technique include the Borum Eshoj Hairnet, found near Aarhus, Denmark and dated to 1400 B.C. 
Also, there is a hairnet found near Vindonissa, Switzerland dated A.D.100, worked with triple twist interlinking. 
When working sprang, more than one twist can be given to each pair of threads. For instance, giving each pair a double twist will result in a diamond pattern if the warp is striped with two colors. The number of twists can be varied to create patterns. This type of sprang tends to be more stable, as the multiple twists don't shift as much as single ones.
At left: double-twist sprang on a two-color warp (Eight blue, eight white, eight blue). This results in alternating diamonds of solid color on a two-color background.
At right: Wool belt patterned with Z-twist on an S-twist background. There are 2 diamond shapes side-by side alternating with rectangles.
Alternating S-and Z-twist
This technique is represented by a couple of woolen tubes dubbed “stockings”. One was found in Norway at Tegle and is made of alternating triangles of S- and Z-twist, dated about 500B.C to 100A.D. The other was found in York, England and is in stripes of S- and Z-twist, dated to the Viking period (A.D.850). There is also a hairnet of the Hallstatt period (800-500 B. C.) found in Arden, Sweden, patterned with stripes of S- and Z-twist. 
The simplest patterns can be made by alternating one or more rows of S-twist with one or more Z-twist rows. This will make the fabric less apt to twist when it comes off the frame. Where each change meets there will be a row of crossed threads unless a double twist is given in the last row before the transition. Patterns of angled borders are possible with this technique, the meeting lines will stand up or fade back, creating a three-dimensional effect.
As described in Collingwood p115-116:
To make a triangle of S-twist on a Z-twist background, start a row of normal Z-twist. When you get to the apex of the triangle, do one S-twist, then continue the row with Z-twist.
The next row will be Z-twist up to the point where you have the two back threads lying next to one another. Work the right-hand one as usual, then make an S-twist with the next 2 front threads, and an S-twist with the next two back threads. Finish the row with Z-twist.
Continue to work the rows the same way; Z-twist to the point where the left-hand of the doubled back threads is next, do the S-twist of the front threads, then S-twist the next front and back threads until you reach the left side of the triangle. Then S-twist the next 2 back threads and Z-twist the rest.
To reverse the pattern and form a diamond:
Z-twist to the usual stopping point, this time Z-twist the two front threads, S-twist one more pair than you did in the previous row, and Z-twist the next two back threads, and finish the row in Z-twist.
In each of the following rows, continue to decrease the number of S-twists, but flank them with a Z-twist of the front and back pairs as in the previous row. Continue until you are back to all Z-twists again.
Artifacts with hole designs include “Queen Grunhild's Hairnet” dated to 800-500 B.C, found in Denmark, and a white linen fabric embroidered with blue thread dated to the 15th century, likely from Switzerland.  Also a valence from the 16th century in the Met Museum. 
Holes can be used as a background for a pattern of regular interlinking, or as a pattern on a solid background.
To make a fabric made of “holes” (described in Collingwood pg132 and Kliot pg9-11):
Start with a “overplait” row, or the usual 1 back, 1 front interlinking.
Z-twist pairs of threads by picking up 2 back and dropping 2 front threads.
Work a row of normal Z-twist.
Z-twist the first front and back thread, then twist pairs across the row. Z-twist the last front and back thread.
Work a row of normal Z-twist.
The holes are across 3 rows of work, so they will be large compared to the regular interlinking. Patterns of holes on a solid background work best as geometric shapes with angled sides.
To work a triangle of holes on a plain background (Collingwood pg135-137):
Work Z-twist to the apex of the triangle, then pick up one back thread and drop 2 front threads, pick up 2 back threads and drop one front thread. Then finish the row with Z-twist.
Work the next row plain.
Work Z-twist until just to the right of the first hole, again pick up one back and drop 2 fronts. Pick up 2 backs and drop 2 fronts. Pick up 2 backs and drop one front. Z-twist to the end of the row.
Work a plain row.
Each pattern row follows the pattern as above, adding another pair twist in each row, and bracketing them with the B/2F and 2B/F twists. Follow each of these rows with a plain row.
This is basically woven with no twist between the threads. The simplest version is over one / under one (in Collingwood's terms). Over two / under two and over three / under three are progressively more stable.
One extant piece I know of is a pair of garters from the 16th century held by the Boston Museum of Fine Arts. It appears to be interlaced in the “Argyle” patterned sections, likely a over two / under two from what I can see in the photos ( http://www.mfa.org/collections/object/garter-one-of-a-pair—121955).
Over one / under one (Collingwood pg 185-6 and Kliot pg 12):
1.Work a normal row starting 2B/F
2.S-twist the first two front threads, S-twist the front and back pairs to the end, then S-twist the two remaining back threads. (Or reverse the frame and do all these maneuvers in Z-twist)
3.Repeat row 1 and 2.
At right: Diagram of over one / under one interlinking
Over two / under two (Collingwood pg 187):
Here we will alternate Z-and S-twist rows as well, but shift over a thread at the beginning;
1.Z-twist the first 2 back threads, Z-twist the rest of the row until the last 2 front threads, give them a Z-twist.
2.Now, you can either reverse the frame and repeat this row, or S-twist the entire row starting with the front two threads and ending with the last 2 back threads.
3.Repeat these two rows.
At right: Diagram of over two / under two interlinking
Over 3 / Under 3 (Collingwood pg 190-1):
1.Start with the two back threads, give a Z-twist to this and all the F/B pairs, then Z-twist the last 2 front threads.
Reverse the frame.
2.Now make a 2B/B twist with the first 3 back threads by passing the two left-most behind the right-hand one. Z-twist the pairs to the end, leaving three front threads. Pick up the left-most thread and pass it behind the other two.
Finally, switch the last thread on the right selvage to the back, and the left-hand selvage thread to the front.
Reverse the frame.
Repeat rows 1 and 2.
Left: A sample of interlinking. The top rows are over one / under one and are quite loose. Following this is a block of regular Z-twist. The herringbone pattern in the next block is over two / under two interlinking and is quite stable. Another block of regular Z-twist follows, ending with a over 3 / under 3 block just above the tassels. This is not stretchy at all, and very stable.
Right: Sample of over two / under two sprang on a striped warp. This also results in alternating diamonds of color. The blue diamonds are twice as big as the white ones because the warp is 8 blue, 8 white, and 8 blue, resulting in twice as many blue threads as white.
Other techniques not included here are twining extra threads (as in Coptic work) and double interlinked sprang.
For further information, I suggest Collingwood's book as the most comprehensive out there. There is also a Sprang yahoo group with useful files and terrific people to answer questions.
Bibliography:Collingwood, Peter 1974. The Techniques of Sprang: Plaiting on Stretched Threads. Faber and Faber Ltd.
For further reference, the Sprang email list at Sprangfirstname.lastname@example.org includes several useful files including a copy of a Sprang Chonology started in Collingwood but added to by Maedb ingen Dungaile (also found here http://www.florilegium.org/?http%3A//www.florilegium.org/files/TEXTILES/sprang-chrono-art.html), and a very thorough bibliography (also found here http://www.cs.vassar.edu/~capriest/sprangbib.html). It also has a number of links and photos by members.