|Two kinds of looms were used in tapestry weaving, the high warp (hautelisse) and low warp loom (basse-lisse). For both methods the basic lines of the cartoon were transferred to a calque, a piece of transparent oiled paper or canvas.
In the high warp technique the lines were again transferred with chalk to the warp threads. By placing mirrors behind the loom and working parallel with the design, the tapestry followed the same direction as the cartoon.
In the low warp technique the calque was turned around and placed under the warp. In either technique the tapestry is produced in the right direction, as the weavers worked parallel with the original cartoon set up behind them. Sometimes the painting was cut into strips and used as a calque. The strips were put under the warps of the low warp loom, so that the weaver could follow the design. In this method, since the weaver worked on the back of the tapestry, the result was a mirror image of the cartoon. Letters and numbers were sometimes reversed on the tapestry, either because weavers and designers forgot this technical detail or simply could not read.
Excerpt from: Rubens and the Traditions of Tapestries. Author: Francoise Hack. 1997.
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