Stone (Solid Inclusions)

• Definition: Opaque solid inclusions within the glass, such as raw material stones, refractory stones, and devitrification crystals.

Knot (Transparent Inclusions)

• Definition: Transparent lumps in the glass caused by uneven mixing of batch materials or incomplete melting.

Cord (Gas Line)

• Definition: Elongated, gas-filled defects typically visible to the naked eye (stretched linear bubbles within the glass).

Scratch (Surface Abrasion)

• Definition: Superficial wear that does not penetrate the glass wall thickness (opaque marks caused by friction with external objects).

Crack (Surface Fracture)

• Definition: Breaks occurring on the surface of the glass tube.

Stress

• Definition: Internal stress caused by non-uniform volume changes in the material’s macro- or microstructure, resulting from temperature variations during tube forming (thermal stress, structural stress, mechanical stress).

Contamination

• Definition: Organic or inorganic substances such as grease, oil, dust, and other visible impurities under normal lighting.

Glass Fragments (Cullet)

• Definition: Glass particles adhering to or embedded in the inner surface of the glass.

Striae (Ream or Wave Marks)

• Definition: Thin, streak-like defects formed when heterogeneous glassy inclusions are dispersed but not fully homogenized during molten glass flow or stirring.

• Note: These glassy inclusions (striae and knots) are common defects related to glass inhomogeneity, differing from the base glass in chemical composition and physical properties (e.g., refractive index).

Rib (Longitudinal Ridge/Valley)

• Definition: A continuous concave or convex line along the tube length caused by imperfections in the feeder bowl or spout.