Medically Reviewed by: Dr. Dipak Ladda, M.D.
Expertise: Consultant Pathologist
Last Updated: August 1, 2026
Medical Analysis
Comprehensive Medical Analysis and Laboratory Guide to Fontana Masson’s Staining
Advanced Histopathological Principles and Mechanistic Pathways of Fontana Masson’s Staining
The Fontana Masson stain is an essential diagnostic tool utilized in pathology laboratories to demonstrate argentaffinic substances, most often melanin, but also argentaffin granules, which are found in carcinoid tumors, in the digestive tract or lung [3, 19]. In an argentaffin reaction, ionic silver is reduced to metallic silver, depositing metallic silver at the reduction site [20]. This complex biochemical reaction effectively demonstrates melanin, argentaffin granules, and lipofuscin with high precision [3, 19]. The fundamental principle relies on the fact that the cells at the target site reduce silver to a visible metallic state without the aid of an external reducing agent [20]. It gets deposited directly at the target and is subsequently identified under microscopic evaluation [3, 20].
Clinical Indications, Diagnostic Applications, and Uses of Fontana Masson’s Stain
This specialized histological staining technique serves multiple critical clinical applications in modern diagnostic medicine [3, 4]. It is widely used to detect melanin of dematiaceous fungi such as Curvularia lunata and Bipolaris hawaiiensis in tissue sections [17]. Furthermore, it identifies those fungi which remain unidentified in H&E stained sections, potentially due to non-evident brown color [17]. It is routinely used to identify argentaffin granules and argentaffinic substances in histological sections for the definitive confirmation of carcinoid tumors [19]. Additionally, it assists clinicians and pathologists to diagnose melanoma and differentiate it from other skin tumors, while also highlighting melanin pigments in benign lesions such as nevi [18].
| Clinical Application | Description |
| Melanin pigment identification | Detects melanin in melanocytic and pigmented lesions for histopathology diagnosis [18]. |
| Fungal infection diagnosis | Visualizes melanin-like pigments in fungi such as Cryptococcus, Malassezia, and others [17]. |
| Pigmentation disorder evaluation | Assesses melanin presence in disorders like pityriasis versicolor and seborrheic dermatitis [18]. |
| Syphilis diagnosis | Detects spirochetes directly via silver impregnation in primary syphilitic chancres [2, 15]. |
| Histochemical differentiation | Differentiates melanins from other pigments (e.g., hemosiderin, lipofuscin) in tissue sections [3, 6]. |
Specimen Collection, Processing Protocols, and Reagents for Fontana Masson Staining
Proper specimen collection and tissue preparation are critical for obtaining reproducible and diagnostically valuable staining results [3, 4]. The procedure typically requires paraffin blocks prepared from ten percent formalin-fixed tissue samples [7]. Four micrometer paraffin sections are the best choice for further laboratory procedures [7]. The preparation of specialized solutions, most notably the ammoniacal silver solution, requires meticulous execution: take twenty milliliters of ten percent silver nitrate in a beaker, add a few drops of strong ammonium hydroxide with continuous stirring, and continue adding slowly drop by drop until the precipitate that is formed dissolves totally [3, 11]. Stop adding and stirring when the precipitate totally dissolves and is seen as faint opalescent, then add twenty milliliters of distilled water [3, 11].
| Material | Quantity |
| Silver nitrate 10% | 10 Gms of AgNO3 + 90 ml DW [3, 11] |
| Strong ammonium hydroxide (s.g. 0.880) | Use as it is [3, 11] |
| Sodium thiosulphate 3% | 3 Gms of Sodium Thiosulfate + 97 ml DW [3, 11] |
| Gold Chloride 0.1% | 100 mgs of AuCl2 + 99.9 ml DW [3, 11] |
| Neutral Red | 100 mgs of Neutral Red + 9.9 ml DW [3, 11] |
| Potassium Permanganate 1% | 1 Gms of K Permanganate in 99 ml DW [3, 11] |
| Sulfuric Acid 3% | 3 ml of Concn H2SO4 in 97 ml of DW [3, 11] |
| Mallory Bleach | Mix 2.5 ml of 3% H2SO4 and 47.5 ml of 1% K Permanganate [3, 13] |
Step-by-Step Staining Procedure and Interpretive Staining Color Profiles
The execution of the staining protocol requires adherence to standard laboratory workflows [3]. Bring sections to water via xylene and ethanol [3]. Remove melanin with Mallory Bleach, bleach in oxalic acid for a few minutes, and rinse with distilled water [3]. Treat with ammoniacal silver for thirty minutes at fifty-six degrees Celsius and rinse again with distilled water [3]. Place in zero point one percent gold chloride for ten seconds, rinse with distilled water, and place in sodium thiosulfate for five minutes for fixation, followed by rinsing with running tap water [3]. Counterstain with zero point one percent Neutral Red solution, rinse with distilled water, rapidly dehydrate with absolute ethanol, clear with xylene, and mount with a resinous medium [3].
| Components | Staining colour |
| Nuclei | Red [3, 11] |
| Melanin (Unbleached) | Black [3, 11] |
| Melanin (Bleached) | Unstained [3, 11] |
| Lipofuscin | Black [3, 11] |
| Enterochromaffin | Black [3, 19] |
| Background | Grey [3, 11] |
Critical Laboratory Precautions, Technical Limitations, and Quality Control
Performing silver impregnation techniques involves handling hazardous chemicals and demands strict safety measures [3, 7]. Essential precautions include using gloves, eye protection, and a lab coat, avoiding the inhalation of fumes or dust, and handling silver nitrate solutions with extreme care [7]. Furthermore, technicians must use clean glassware, avoid metal tools, dispose of waste in accordance with hazardous chemical rules, and store reagents tightly sealed and refrigerated [3, 7]. Despite its utility, the method has limitations: specificity is questionable as it also stains lipofuscin, hemosiderin, and other pigments [3, 6]. It has limited application pertaining exclusively to melanin pigment detection, presenting quantitative limitations, poor results on fresh tissues, and a strong dependency on expert interpretation to avoid diagnostic variability [3, 19].
For Non-Medicos
Quick Guide to Understanding Fontana Masson’s Staining
What Is Fontana Masson Staining?
Fontana Masson staining is a specialized laboratory method used by doctors and scientists to color specific microscopic structures in tissue samples [3]. It is most famous for highlighting melanin, the pigment that gives skin and hair its color, as well as finding specific granules linked to tumors or certain fungal infections [3, 17, 19].
Why Do Doctors Use This Test?
Medical professionals order this stain to get clear answers when complex skin, lung, or digestive tract conditions are suspected [3, 17, 18, 19]. It helps identify dangerous skin cancers like melanoma, confirms the presence of carcinoid tumors, detects hidden fungal infections that regular stains miss, and differentiates various types of tissue pigments [3, 17, 18, 19].
How Tissue Samples Are Prepared and Stained
To perform the test, tissue samples are preserved, embedded in wax, and sliced into paper-thin layers [3, 7]. These slices undergo a careful chemical process using specialized reagents like silver solutions and neutral red [3, 11]. The target substances naturally react with the silver, turning dark or black so they stand out clearly under a microscope against a grey or red background [3, 11, 20].
Safety Measures and Test Limitations
Because this procedure involves strong chemicals like silver nitrate and acids, laboratory technicians must wear protective gear, handle waste safely, and carefully control every step [3, 7]. While incredibly useful, the test has limitations: it requires expert interpretation because other pigments can sometimes mimic melanin, and it cannot be performed effectively on fresh, unfixed tissue samples [3, 19].
References
Masson, P. (1929). Some histological methods of trichrome staining and their application to normal and pathological tissues. Journal of Technical Methods, 12, 75–90.
Fontana, A. (1912). Verfahren zur intensiven Färbung der Spirochaeta pallida (Treponema pallidum) in Schnittpräparaten. Dermatologische Wochenschrift, 55(41), 1203–1204.
Bancroft, J. D., & Gamble, M. (2008). Theory and Practice of Histological Techniques (6th ed.). Churchill Livingstone Elsevier.
Suvarna, S. K., Layton, C., & Bancroft, J. D. (2018). Bancroft’s Theory and Practice of Histological Techniques (8th ed.). Elsevier.
Carson, F. L., & Cappell, C. (2015). Histotechnology: A Self-Instructional Text (4th ed.). American Society for Clinical Pathology (ASCP) Press.
Lillie, R. D. (1977). H. J. Conn’s Biological Stains (9th ed.). Williams & Wilkins.
Armed Forces Institute of Pathology (AFIP). (1992). Laboratory Methods in Histotechnology. American Registry of Pathology.
Sheehan, D. C., & Hrapchak, B. B. (1980). Theory and Practice of Histotechnology (2nd ed.). Battelle Press.
Culling, C. F. A., Allison, R.T., & Barr, W. T. (1985). Cellular Pathology Technique (4th ed.). Butterworths.
Horobin, R. W. (1982). Histochemistry: An Explanatory Outline of Histochemical and Histological Staining. Gustav Fischer Verlag.
Luna, L. G. (1968). Manual of Histologic Staining Methods of the Armed Forces Institute of Pathology (3rd ed.). McGraw-Hill.
Kiernan, J. A. (2015). Histological and Histochemical Methods: Theory and Practice (5th ed.). Scion Publishing.
Mallory, F. B. (1938). Pathological Technique. W.B. Saunders Company.
Romeis, B. (1989). Mikroskopische Technik (17th ed.). Urban & Schwarzenberg.
Gridley, M. F. (1953). A modification of the Fontana stain for Treponema pallidum. American Journal of Clinical Pathology, 23(3), 303–307.
Prentø, P. (2009). Staining of connective tissue: Mechanistic aspects of trichrome and silver staining. Biotechnic & Histochemistry, 84(3), 125–132.
Chandler, F. W., & Kaplan, W. (1987). Decolorization and Staining Methods for Fungi in Tissue Sections. Centers for Disease Control and Prevention.
Lever, W. F., & Schaumburg-Lever, G. (1990). Histopathology of the Skin (7th ed.). J.B. Lippincott Company.
Sokal, J. E., & Gilman, A. (1995). Histochemical identification of argentaffin granules and melanin pigments in neoplasms. Journal of Histotechnology, 18(2), 115–120.
Avwioro, G. (2011). Histochemical uses of silver impregnation techniques: A review. JP Journal of Biostatistical Sciences, 5(2), 125–136.
FAQ’s:
1. What is Fontana Masson staining?
A laboratory method used to demonstrate melanin and argentaffinic substances in tissue sections.
2. How does the staining work?
Ionic silver is reduced to metallic silver at the target site without a reducing agent.
3. What samples are required?
Paraffin blocks prepared from 10% formalin-fixed tissue samples, ideally four-micrometer sections.
4. What are the key reagents?
Reagents include silver nitrate, strong ammonium hydroxide, sodium thiosulphate, gold chloride, and Mallory bleach.
5. What safety precautions are needed?
Use gloves, eye protection, a lab coat, avoid fumes, and handle silver nitrate carefully.
6. How is the solution prepared?
Add ammonium hydroxide dropwise to silver nitrate until precipitate dissolves, leaving a faint opalescence.
7. What are the staining steps?
Treat with ammoniacal silver, gold chloride, sodium thiosulfate fixation, and neutral red counterstaining.
8. What are the color profiles?
Nuclei stain red, unbleached melanin and lipofuscin appear black, and the background is grey.
9. What are its clinical applications?
It identifies melanin, diagnoses fungal infections, evaluates pigmentation disorders, and detects carcinoid tumors.
10. What are the method limitations?
Questionable specificity, limited quantitative application, poor fresh tissue results, and reliance on expert interpretation.
