Permanent ink in an ultrafine tip is ideal for labeling microscope slides and cassettes. StatMark Pens are made of rigid nylon that allow for precise hand marking on glass slides as well as on most tissue embedding cassettes. This quick drying ink is highly resistant to aqueous based stains, alcohols, xylene and xylene substitutes. StatMark Pens do not dry out easily and last twice as long as many of the leading 'laboratory' pens.