Overview
ISO 9184-3:1990 specifies the Herzberg staining test used in fibre furnish analysis for paper, board and pulps. It defines preparation, use and colour reactions of the Herzberg stain and is intended to be used together with ISO 9184-1 (general method) and, where needed, ISO 9184-2 (staining guide). The test provides qualitative and quantitative differentiation between chemical, mechanical and rag pulps, helps identify semi-chemical pulps, and distinguishes regenerated cellulose (e.g., viscose) from synthetic fibres.
Key topics and requirements
- Scope and purpose: Apply Herzberg stain for fibre identification in pulp and paper furnish analysis.
- Reagents and preparation:
- Zinc chloride solution: prepare saturated ZnCl2 in warm water (allow some crystallization on cooling); store in a brown reagent bottle.
- Iodine solution: prepare from potassium iodide (2.1 g KI + 0.1 g I2) with water added dropwise to dissolve iodine.
- Herzberg stain: mix the zinc chloride solution, a small amount of water and the iodine solution; allow precipitate to settle, decant the clear solution, add an iodine flake and keep in the dark. Prepare fresh every two months.
- Safety: Some components are toxic - prepare and handle the stain following safe laboratory practice.
- Procedure:
- Stain fibre slides prepared per ISO 9184-1 with 2–3 drops of Herzberg stain.
- Examine microscopically at magnifications of about x40 to x120.
- Identify and count fibres according to ISO 9184-1 and report results accordingly.
- Colour interpretation (typical):
- Chemical pulp: blue to bluish‑violet
- Mechanical pulp: yellow
- Rag pulps (cotton/linen/hemp/ramie): wine‑red
- Semi‑chemical/chemi‑mechanical: dull/mottled blue and yellow or dark bluish‑violet
- Regenerated cellulose (viscose): yellow
- Synthetic fibres: colourless to brownish‑yellow
- Note: colours can shift over time (blue darkens, yellow greys); stain strength may need small adjustments.
Applications and users
- Paper and board manufacturers performing fibre furnish quality control
- Pulp mills and laboratories verifying fibre composition and pulping efficiency
- Forensic and conservation labs assessing paper components and contamination
- R&D and process control teams needing rapid microscopic differentiation of fibre types
Keywords: ISO 9184-3:1990, Herzberg staining test, fibre furnish analysis, pulp differentiation, paper pulp testing, staining reagents, zinc chloride iodine stain, microscopic fibre identification.
Related standards
- ISO 9184-1: General method for fibre furnish analysis
- ISO 9184-2: Staining guide
- Other parts of ISO 9184 (Parts 4–7) cover alternative stains and weighting methods for furnish analysis.
