ASTM C1048 — Standard Specification for Heat-Treated Flat Glass

GLASS QUALITY INSPECTOR

Roller Wave · Edge Lift · Stress · Zebra Mark Analysis

What is ASTM C1048?

ASTM C1048 is the standard specification governing Heat-Treated Flat Glass — including Heat-Strengthened (HS) and Fully Tempered (FT) glass. It establishes allowable limits for optical distortions (roller wave, edge lift), surface quality (zebra marks), and mechanical properties for architectural applications.

Key Insight: Optical distortion in heat-treated glass results from the roller hearth tempering process. As hot glass passes over rollers, thermal gradients cause localized bending. The frequency and amplitude of these waves determine glass quality.

Glass Types Covered

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Kind HS

Heat Strengthened

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Kind FT

Fully Tempered

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Spandrel

Opaque Zones

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Coated

Low-E / Solar

Property	Heat Strengthened	Fully Tempered
Surface Compression (PSI)	3,500 – 7,500	≥ 10,000
Surface Compression (MPa)	24 – 52	≥ 69
Edge Compression	Not specified	≥ 9,700 PSI
Break Pattern	Large pieces	Small dice
Strength vs Annealed	~2×	~4×

Quick Reference — ASTM Limits

Parameter	Limit	Unit
Max Roller Wave Depth	≤ 0.076	mm (0.003")
Zebra Mark Width	≤ 1/16"	inch
Edge Lift (per 300mm)	≤ 1.5	mm
Bow (overall)	≤ 0.5%	of length
Warp (per 300mm)	≤ 1.2	mm
Max Scratch Width	≤ 1/32"	inch
Roller Pitch Typical	57–83	mm
Wave Height (premium)	≤ 0.038	mm

How Roller Wave Forms

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Step 1 — Heating

Glass enters furnace at ~650°C. Rollers support the softened glass. Uneven heat transfer creates micro-deformations at each roller contact point.

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Step 2 — Quenching

Air nozzles rapidly cool surfaces. The contact-point deformations "freeze" into the glass. The pitch distance between waves = roller spacing.

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Step 3 — Result

Installed glass reflects light at slightly varying angles. In long facade reflections (buildings/sky), roller wave appears as periodic waviness or zebra bands.

Measurement Methods

Method	Principle	Accuracy
Zebra Board	B/W stripe reflection	Visual / subjective
Laser Profilometer	Contact/non-contact scan	±0.001 mm
Shadow Moiré	Fringe pattern analysis	±0.005 mm
Digital Deflectometry	Screen + camera + algorithm	±0.002 mm
Babinet Compensator	Polarized light stress	Stress birefringence

Industry Standards Comparison

Standard	Region	Max Wave
ASTM C1048	USA/Americas	0.076 mm
EN 12150	Europe	0.10 mm
GB 11614	China	0.10 mm
AS/NZS 4667	Australia	0.076 mm
SGCC Premium	Industry	0.038 mm

Glass Sample Input

Glass Length (mm)

Glass Width (mm)

Glass Thickness (mm)

Glass Type

📐 Measurement Values

Roller Wave Depth (mm) i

Edge Lift per 300mm (mm) i

Overall Bow (mm) i

Surface Stress (MPa) i

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Enter your glass measurements
and click Analyze Glass Quality
to see the full quality report

Roller Wave Quality Classification Table

Quality Grade	Roller Wave (mm)	Roller Wave (inch)	Edge Lift / 300mm	ASTM Status	Typical Application
✦ Excellent	< 0.025 mm	< 0.001"	< 0.5 mm	✔ Exceeds Standard	Ultra-premium facades, museums, luxury hotels
★ Best	0.025 – 0.038 mm	0.001 – 0.0015"	0.5 – 0.8 mm	✔ Exceeds Standard	High-end curtain wall, premium residential
● Good	0.038 – 0.055 mm	0.0015 – 0.002"	0.8 – 1.2 mm	✔ Compliant	Commercial facades, standard curtain wall
◆ Medium	0.055 – 0.076 mm	0.002 – 0.003"	1.2 – 1.5 mm	⚠ At Limit	Interior partitions, low-visibility areas
▲ Pass	0.076 mm (exactly)	0.003"	1.5 mm (exactly)	⚠ Borderline	Non-critical glazing, review with client
✖ REJECT	> 0.076 mm	> 0.003"	> 1.5 mm	✘ Non-Compliant	DO NOT USE — Return to manufacturer

✦ EXCELLENT

★ BEST

● GOOD

◆ MEDIUM

▲ PASS

✖ REJECT

        ← 0.000 mm (Perfect Flat)
        0.076 mm ASTM Limit →
      

Understanding Glass Reflections

Optical distortion in heat-treated glass is most visible when observing reflections of long horizontal lines — such as adjacent buildings, horizon lines, or road edges. The examples below demonstrate how roller wave distortion manifests in real-world facades.

Observation Rule: Stand 3–6 meters from the glass. Look at reflections of straight horizontal or vertical lines (buildings, mullions, skyline). Any waviness you see in those reflected lines is caused by roller wave distortion in the glass surface.

✦ Excellent Quality Reflection

Building reflections appear crisp and perfectly straight. No waviness detected. Roller wave depth < 0.025mm. Ideal for premium high-rise facades, museums, and luxury hotels. Achievable with ultra-flat roller hearth furnaces.

✖ Rejected — Non-Compliant Reflection

Building reflections show severe wave distortion. Horizontal lines of adjacent buildings appear wavy and irregular. Roller wave depth > 0.076mm. Fails ASTM C1048. Glass must be rejected and returned to manufacturer.

● Good Quality Reflection

Reflections are nearly straight with only minor, barely noticeable undulation. Roller wave 0.038–0.055mm. Fully ASTM C1048 compliant. Suitable for most commercial curtain wall and standard facade applications.

◆ Medium Quality — At the ASTM Limit

Visible wave distortion in reflected building lines. Roller wave 0.055–0.076mm. Technically passes ASTM C1048 but noticeable in high-reflectivity glazing. Discuss with client before installation in visible facades.

What Are Zebra Marks?

Zebra marks are periodic dark and light bands visible on heat-treated glass surfaces when viewed under specific lighting. They result from roller contact imprints during the tempering process — slight variations in surface flatness caused by each roller.

Test Method: View the glass at a shallow angle (15–30°) against a uniform bright background or fluorescent light ceiling. Zebra-pattern inspection boards (alternating black/white stripes at 25mm intervals) reveal distortion by showing wave amplitude in stripe reflections.

Stripe Width on Board	Reveals	Use Case
25 mm stripes	Major waves only	Standard acceptance
12.5 mm stripes	Medium distortion	Premium facades
6 mm stripes	Minor distortion	Ultra-premium spec

Live Zebra Pattern Simulator

Wave Amplitude (distortion level)

              0 — Perfect530 — Rejected
            

Zebra Board Inspection Protocol

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Viewing Distance

Stand 3–5 meters from glass. For large panes, increase to 6–8 m. Too close exaggerates distortion; too far masks it.

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Lighting Condition

Use diffuse overcast sky or uniform fluorescent bank. Avoid direct sunlight which creates glare and masks defects.

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Board Angle

Hold zebra board at 90° to glass, parallel to roller travel direction. Rotate 90° to check both axes of distortion.

Mark Width Observed	ASTM C1048 Limit	Assessment	Action
< 1.0 mm	≤ 1.59 mm (1/16")	Excellent	Accept — Premium quality
1.0 – 1.59 mm	≤ 1.59 mm (1/16")	Compliant	Accept — Standard quality
1.59 – 2.0 mm	Exceeds limit	Borderline	Verify with profilometer
> 2.0 mm	Exceeds limit	Reject	Return to manufacturer

Surface Stress & Anisotropy Calculator

Measured Surface Stress (MPa)

Glass Treatment Type

Retardation Value (nm) — for anisotropy

Glass Thickness for stress calc (mm)

ASTM C1048 Stress Requirements

Glass Type	Surface Compression	Edge Compression	Center Tension	Status Zone
Fully Tempered (FT)	≥ 69 MPa (10,000 PSI)	≥ 67 MPa (9,700 PSI)	~34 MPa	ASTM Minimum
Heat Strengthened (HS)	24 – 52 MPa (3,500–7,500 PSI)	Not specified	~12–26 MPa	Range Required
Premium FT	≥ 90 MPa	≥ 85 MPa	~45 MPa	Exceeds Standard
Annealed (AN)	Not applicable	N/A	N/A	Not Heat-Treated

Anisotropy Note: When fully tempered glass is viewed through polarized lenses (polarized sunglasses), iridescent color patterns may appear — this is called anisotropy or "quench marks." It is a normal characteristic of tempered glass, not a defect, and is not addressed in ASTM C1048. However, many project specifications limit visible anisotropy retardation to <15nm for premium facades.

Retardation (nm)	Visibility	Assessment	Application Suitability
< 5 nm	Not visible	Excellent	All applications including luxury
5 – 15 nm	Barely perceptible	Premium	High-end facades, premium spec
15 – 30 nm	Visible in polarized light	Standard	Standard commercial glazing
30 – 60 nm	Clearly visible	Noticeable	Non-critical, discuss with client
> 60 nm	Prominent colors	Discuss	May be rejected on premium projects

ASTM C1048 Complete Reference — Flatness & Optical Distortion

Section	Parameter	Limit / Requirement	Test Method	Notes
§6.1	Roller Wave Depth	≤ 0.076 mm (0.003")	Profilometer / laser scan	Measured over 300mm gauge length
§6.2	Edge Lift	≤ 1.5 mm per 300mm	Straight edge + feeler gauge	Within 25mm of any edge
§6.3	Overall Bow	≤ 0.5% of largest dim.	String line measurement	e.g. 2400mm pane: ≤12mm
§6.4	Warp	≤ 1.2 mm per 300mm	Dial indicator scan	Applies to diagonal measurement
§7.1	Surface Compression (FT)	≥ 69 MPa (10,000 PSI)	Polarimeter / surface wave	ASTM C1279, ASTM C1422
§7.1	Surface Compression (HS)	24–52 MPa	Polarimeter	Must not exceed 52 MPa upper limit
§7.2	Edge Compression (FT)	≥ 67 MPa (9,700 PSI)	Scattered light polariscope	ASTM C1279
§8.1	Zebra Mark Width	≤ 1.59 mm (1/16")	Visual — zebra board	25mm stripe pitch, 5m distance
§8.2	Scratch Depth	≤ 0.79 mm (1/32")	Optical comparator	Maximum individual scratch
§8.3	Pits / Chips	≤ 3.2 mm (1/8") dia	Visual inspection	No more than 2 per 1 m²
§9	Break Pattern (FT)	≥ 40 particles per 50×50mm	ANSI Z97.1 drop test	Minimum fragment count
§10	Sampling Rate	AQL Level II	ANSI/ASQ Z1.4	Per lot inspection protocol

Edge Lift — Measurement Guide

Edge lift is the deviation of the glass edge from a flat reference surface, measured within 25mm of any edge, over a 300mm gauge length.

Edge Lift/300mm	Grade	ASTM Status
< 0.5 mm	Excellent	✔ Pass
0.5 – 0.8 mm	Best	✔ Pass
0.8 – 1.2 mm	Good	✔ Pass
1.2 – 1.5 mm	Medium	⚠ Borderline
> 1.5 mm	Reject	✘ Fail

Related Standards Cross-Reference

Standard	Topic
ASTM C1036	Flat Glass — Annealed base standard
ASTM C1048	Heat-Treated Flat Glass (this standard)
ASTM C1279	Stress measurement by polarimetry
ASTM C1422	Chemically strengthened flat glass
ANSI Z97.1	Safety glazing materials performance
EN 12150	European tempered glass standard
SGCC	Safety Glazing Certification Council
GANA	Glass Assoc. of N. America guidelines

Inspection Checklist — On-Site Glass Acceptance

✅ Required Checks

Verify glass markings / etch — confirm HS or FT designation

Measure roller wave depth with profilometer or laser scan

Measure edge lift at all 4 edges with feeler gauge and straight edge

Perform zebra board visual inspection at 3–5m distance

Verify surface compression stress with polarimeter (per ASTM C1279)

Inspect for surface defects: scratches, chips, pits, stains

Measure overall bow and warp per §6.3/6.4

Confirm mill certificate / test report from manufacturer

⚠ Automatic Rejection Criteria

🚫 Roller wave depth > 0.076 mm
🚫 Edge lift > 1.5 mm per 300 mm
🚫 Surface stress (FT) < 69 MPa
🚫 Surface stress (HS) < 24 MPa or > 52 MPa
🚫 Break pattern < 40 pieces per 50×50mm (FT)
🚫 Zebra mark width > 1.59 mm (1/16")
🚫 Scratches > 0.79 mm (1/32") width
🚫 Overall bow > 0.5% of largest dimension
🚫 Missing or unreadable ASTM/SGCC etch mark
🚫 Visible edge chips or cracks of any size

Documentation Required: Mill test certificates, stress reports, and inspection records must be retained for the project duration. Non-compliant glass must be tagged, quarantined, and returned with written NCR (Non-Conformance Report).