苏木精, 或 C.I. 75290，无色或淡灰黄色粉末，本身不是一种染料，由采木的心材提取。氧化形成苏木红，后者与某些特定金属离子（主要为Fe（III）与Al（III））结合形成有色复合物。 用来给细胞核染色从而可在显微镜下观察。

苏木精-伊红染色 在组织学中很常用，可以将细胞核染上深紫色，而且染色步骤并不复杂。染色是永久性的（而碘化钾碘溶液染色是暂时性的）。

1970年代，由于过度砍伐巴西和中美洲的森林造成了采木的短缺，苏木精因而价格飙升，组织病理学的诊断成本升高，人们开始寻找其他核染色的方法。代替品尚未找到，采木产量又回升了，苏木精重新回归人们的视线，虽然价格较之前高了些。其他推荐的代替物包括Celestine blue B (CI 51050), Gallocyanin (CI 51030), Gallein (CI 45445) 和 Solochrome cyanin (CI 43820). 四种染料都用Fe(III)做媒染剂，亦可选用红色染料brazilin，只和苏木精相差一个羟基。

Haematoxylin or hematoxylin (/ˌhiːməˈtɒksᵻlᵻn/), also called natural black 1 or C.I. 75290, is a compound extracted from the heartwood of the logwood tree (Haematoxylum campechianum). Hematoxylin is a basic and positively charged compound that binds to and forms salts with acidic (basophilic) compounds containing negative charges (such as DNA and RNA, which are acidic/negative because the nucleic acid building blocks that come off the phosphate backbone are negatively charged) and stains them dark blue or violet. Haematoxylin and eosin together make up haematoxylin and eosin stain, one of the most commonly used stains in histology. This type of stain is a permanent stain as opposed to temporary stains (e.g. iodine solution in KI). Another common stain is phosphotungstic acid haematoxylin, a mix of haematoxylin with phosphotungstic acid. When oxidized it forms haematein, a compound that forms strongly coloured complexes with certain metal ions, the most notable ones being Fe(III) and Al(III) salts. Metal-haematein complexes are used to stain cell nuclei prior to examination under a microscope. Structures that stain with iron- or aluminium-haematein are often called basophilic, even though the mechanism of the staining is different from that of staining with basic dyes.