In the early years of the eighteenth century the Dutch method of bleaching required up to five months to produce white cloth. All the work was done by hand and the bleaching materials were potash (obtained from wood ashes) for the alkali ley (bleaching liquid) and buttermilk or bran sour for the acids to neutralise them. Much time was spent then in boiling the pieces over great turf fires and then rinsing them in clear cold water. The annual output of the largest bleach-greens would not have exceeded one thousand pieces.
In the 1730s bleachers began to adapt the heavy wooden machinery of the local `tuck' mills (for finishing woollens) to prepare their linen cloth: although the Linen Board was anything but enthusiastic, wash mills and rubbing boards came into general use. The beetling engine for finishing off the quality linens with a glaze appeared about the same time. All this machinery has survived in use into the twenty-first century. More important even than machinery in increasing the output of the bleach greens was the chemical revolution that greatly reduced the time required for bleaching. For neutralising the alkalis based on potash, dilute sulphuric acid (known then as `oil of vitriol') replaced buttermilk in the 1760s and by the close of the century a new bleaching liquor derived from chlorine reduced the time required for souring from several weeks to a single day. By the end of the century some greens could turn over ten thousand pieces each year, and this output continued to increase.