Encyclopedia of the Incas

lower end of which was affixed a spindle whorl (piruru) commonly made of
stone, ceramic, or wood. The raw fibers were held in the free hand and stretched
and fed out to the hand holding the drop spindle. The spindle was dropped while
spun rapidly and the raw fibers formed a thinly spun thread.
Spun and plied threads are commonly described as either S or Z. These
notations are used to indicate whether the spindle is dropped and spun to the
right (clockwise) to produce fibers within the thread body that run obliquely
from upper left to lower right, like the slant of an S, or if the spindle is dropped
and spun counterclockwise, producing threads with oblique axes running upper
right to lower left, like the slant of a Z. Inca thread of the south highlands and
coast was generally spun in the Z direction. Two or three Z-spun threads would
be twisted together, using the drop spindle, in the S-direction to produce Z-
spun/S-plied threads for weaving. North coast Chimú weavers, contemporary
with the Incas, commonly prepared threads S-spun/Z-plied. Spun and plied
camelid threads (but only infrequently those made of cotton) would often be
dyed before warping began.
Warping is the process of extending a continuous warp thread back and forth
across a frame often composed of a pair of stakes embedded upright in the
ground, or across a horizontal frame, to provide the fixed, lengthwise threads
through which the weft threads pass in the act of weaving. The warped threads
of a textile contain a thread crossing (often called sonqo, heart) at the center of
the warping. It is this crossing that, in plain weave textiles, will be worked up
and down by the heddles to alternately raise and lower groups of warp threads
through which the weft is passed producing the fabric surface (warp + weft).
Inca textiles are woven so finely and tightly that it is often extremely difficult to
tell which group of threads constitute the warp component and which the weft.
The Andean textile specialist Ann Rowe has provided a detailed discussion of
the determination of warp vs. weft in a variety of Inca textiles.