Hematoxylin is a naturally occurring stain extracted from the logwood tree. For use in staining, the hematoxylin is oxidized to hematein which combines with the mordant and is the active staining ingredient. The usual mordants are aluminum salts. Gills hematoxylin uses aluminum sulfate as the mordant and does not contain mercury. It comes in three strengths, Gill’s #1, Gill’s #2 and Gill’s # 3. Gill’s # 1 is the weakest and is used in cytology while the other two are commonly used in histology. These items are manufactured in the United States by Medical Chemical Corp