Selleger Stain

Microscopic Interaction

Acidified calcium nitrate acts as a swelling agent that opens the microscopic pore structure of cellulose microfibrils, facilitating rapid iodine penetration into the plant cell walls. Highly lignified unbleached groundwood, thermomechanical pulp, and raw straw fibres absorb iodine without developing the blue charge-transfer complex, remaining bright yellow under illumination. Bleached kraft and sulphite fibres, having had virtually all lignin stripped during delignification, exhibit an intense pink, wine-red, or deep blue coloration.

Rag, cotton, and bast fibres stain light purple to claret, allowing rapid distinction from chemical wood pulp in historic or high-security document papers.

Furnish Analysis

Identifying unknown packaging paperboard furnishes requires boiling sample scraps, defibring the pulp mechanically, and applying drops of the solution onto mounted microscope glass slides. Verifying the ratio of bleached hardwood kraft to softwood kraft in multi-ply folding boxboard ensures compliance with specified ply stiffness and runnability metrics. Because the solution reacts sharply to trace levels of residual lignin, technicians verify cooking uniformity and trace unbleached fiber cross-contamination within white outer liners.

The method eliminates ambiguity when checking recycled board furnishes for prohibited mechanical wood fractions that reduce folding endurance and structural crease strength.