The latex, which is usually coagulated by standing or by heating, is obtained from incisions in the bark of the tree.
That which flows from the lower incisions is often collected on tiles or on a concave piece of the prickly pear (Opuntia), but is less crystalline and more glutinous, and is less esteemed.
A second method uses several smaller incisions in the scalp.
In copperplate printing the whole of the plate is first inked, the flat surface is then cleaned, leaving ink in the incisions or trenches cut by the engraver, so that, when dampened paper is laid over the plate and pressure is brought to bear, the paper sinks into the incisions and takes up the ink, which makes an impression in line or lines on the paper.
It was found that the method yielding the best results was to make incisions in the poppy-heads soon after sunrise, to collect the juice with the finger immediately after incision and evaporate it as speedily as possible, the colour of the opium being lighter and the percentage of morphia greater than when the juice was allowed to dry on the plant.
