This lofts the wool fibers, and untwists other fibers such as floss and other divisible threads. The threads should first be cut to their working length. After each strand has been separated, reassemble the strands based on the number of ply appropriate for the canvas size.
Silk is sensitive to sun and wet blocking.
Measuring wool amounts for canvas is part mathematics, part educated guess. This may need to be multiplied by number of ply if more than one strand is necessary to fill each hole well. The tension of your stitches is very important to the quality of your finished product. Let each thread rest on the canvas flat and smooth. Tugging is not needed and will distort the canvas threads badly and make your work perhaps nearly impossible to be made up when finishing.