Gilders cotton is used heavily by gilders for polishing the gilded area when the agate stone is not allowed to be use. After you finish gilding, use this cotton yarn to remove excess gold or silver, lightly pounce down the leaf until all flaps of gold that did not stick down are gone.
You should also use the cotton in order to blend in and hide any minor blemishes or imperfections. Use only clean cotton that has not been used before to prevent scratching the finished gilded area.
You can also use this cotton to polish the gesso or the clay layer to get nice and smooth finish before you apply the metal leaf.
About the size of large coconut.