Before a cotton warp can be mounted on the loom, the limp threads must be made stiff enough to stand the passage of the shuttle holding the weft. This is done by sizing the stretched warp with starch, and in the traditional handweaving process it is done by hand, laying out the warp along the street ['street-sizing', which is the reason traditional weaving villages are laid out along straght lines], spraying on the starch and then spreading it evenly with a sizing brush. In different parts of India different starches are used - wheat, millet or rice. Sizing usually happens in the early mornings before the sun is too hot.
Here are some pictures of a malkha warp being rolled up after being sized by the weaver family.