Overview - ISO 16293-2:2025 (Float glass)
ISO 16293-2:2025, “Glass in building - Basic soda lime silicate glass products - Part 2: Float glass,” specifies the dimensional and minimum quality requirements (optical and visual) for float glass used in building applications. It applies to float glass supplied as stock sizes, oversize, and final cut sizes. This second edition introduces provisions for thin glass (< 2 mm), updates defect descriptions, and revises halo measurement for spot faults.
Key topics and technical requirements
- Scope and definitions
- Builds on ISO 16293-1 for terminology and general properties of soda‑lime silicate glass.
- Thickness
- Measurement precision: 0.01 mm (online or offline).
- Off-line thickness = average of four centre measurements.
- Tolerances depend on nominal thickness (e.g., ±0.1 mm for e < 2.0 mm; wider tolerances for thicker glass up to ±1.2 mm).
- Length, width and squareness
- Stock sizes: typical tolerance ±5 mm on nominal L and W.
- Final cut/supplied sizes: tighter tolerances depending on thickness and pane size (examples in standard: ±2 mm to ±5 mm ranges).
- Squareness limits expressed as allowable difference between diagonals (tables by thickness and size).
- Quality requirements (one defined quality level)
- Optical imperfection: measured using the “zebra” test (black/white striped translucent screen). Typical setup: stripes 25 mm wide, screen illumination 400–1 200 lx, glass centre at 4.5 m from screen, observer at 9 m; angle of distortion (α) is recorded.
- Visual blemish:
- Spot blemish: nucleus and halo measured; categories defined by nucleus and halo diameters (e.g., nucleus ≤1.0 mm with halo ≤3.0 mm up to nucleus >3.0 mm with halo >9.0 mm).
- Linear/extended blemish: assessed against a matt black backdrop with the observer 2 m from the pane.
- Edge imperfections (final cut sizes): chips, corner breaks, beaks, bevels with measured limits.
- Designation and measurement methods
- Annex A: informative method for measuring the halo size of spot faults.
Applications and who uses this standard
ISO 16293-2:2025 is used by:
- Glass manufacturers and float glass producers (quality control, production tolerances)
- Glass processors and fabricators (cutting, edging, tempering, insulating glass manufacture)
- Architects, façade and curtain‑wall engineers (specifying glazing performance and visual quality)
- Building product specifiers and procurement teams (acceptance criteria for supplied panes)
- Inspectors and testing laboratories (optical distortion and blemish assessment)
Practical uses include establishing acceptance criteria for delivered glass, guiding inspection procedures, and ensuring consistent visual and optical quality in architectural glazing.
Related standards
- ISO 16293-1 - Definitions and general physical and mechanical properties for basic soda lime silicate glass products (referenced normative document).
Keywords: ISO 16293-2:2025, float glass, glass in building, dimensional requirements, optical quality, visual blemish, thickness tolerances, zebra test, soda lime silicate glass.
