Activity 001: Glass Scoring, Breaking, and Grinding Practice

Activity ID: U12M2-ACT-001 Duration: 45 minutes

Overview

Students practice scoring, breaking, and grinding glass to produce accurately shaped pieces from a simple geometric pattern. This hands-on activity builds fundamental cold glass skills: consistent scoring pressure, clean breaking technique, and safe wet grinding to finished edges suitable for copper foil application.

Materials & Equipment Needed

• Soda-lime glass sheets (clear, 3mm thickness), 12" x 12" per student
• Pattern templates (simple geometric shapes: squares, triangles, gentle curves)
• Glass cutters (carbide wheel, self-oiling preferred)
• Cutting oil (if cutters are not self-oiling)
• Cork-backed metal straightedge rulers
• Running pliers
• Grozing pliers
• Glass grinder (tabletop diamond bit, wet) — one per 2-3 students
• Water supply for grinder reservoirs
• Safety glasses (mandatory)
• Cut-resistant gloves (optional, for handling broken pieces)
• Pattern paper and fine-tip marker
• Glass waste container (clearly labeled)
• Whisk broom and dustpan for glass fragments
• Paper towels

Instructions & Procedure

Part 1: Straight Scoring and Breaking (15 minutes)

1. Students place glass on a clean, flat cutting surface with pattern template visible beneath
2. Instructor demonstrates: position straightedge, hold cutter at 90 degrees, apply consistent pressure, single pass edge-to-edge
3. Students practice straight scores on scrap glass (at least 3 practice scores before pattern cutting):
4. Listen for the correct sound (faint scratch, not grinding or silence)
5. Observe the score line (thin, consistent, no white chips)
6. After scoring, students use running pliers to break along the score:
7. Score line faces up
8. Pliers centered on score line at one end
9. Gentle, even squeeze — crack should run along the score
10. Students cut three straight-edged pieces matching the square/rectangle templates

Part 2: Curved Scoring and Breaking (15 minutes)

1. Instructor demonstrates curved scoring technique: continuous motion following the curve, maintaining consistent pressure throughout the arc
2. Students practice gentle outside curves first (easier — the fracture follows naturally)
3. For inside curves, instructor demonstrates the nibbling technique:
4. Score the primary curve line
5. Score several straight relief lines from the glass edge to the curve
6. Break away relief sections one at a time using grozing pliers
7. Final edge approximates the curve and will be refined by grinding
8. Students cut two curved pieces matching the template

Part 3: Wet Grinding to Pattern (15 minutes)

1. Instructor demonstrates glass grinder operation:
2. Check water level (bit contact point must be submerged)
3. Light pressure — feed glass slowly against the spinning bit
4. Move glass smoothly along the edge, not in one spot
5. Students grind all five cut pieces to match their templates exactly:
6. Remove score line ridges and sharp edges
7. Shape curves to match template
8. Verify fit by placing ground piece over template
9. Students check each piece for:
10. Even edge texture (no chips or gouges)
11. Accurate match to template (within 1mm)
12. No sharp protrusions remaining

Discussion Points

• What happened when you pressed too hard or too lightly during scoring?
• How did the break quality differ between your first and last scores? What changed?
• Why is the nibbling technique necessary for inside curves?
• How does grinding pressure affect edge quality?
• What would happen if the water ran out during grinding?

Expected Outcomes

• Students produce 5 accurately shaped glass pieces that match templates within 1mm tolerance
• Students demonstrate consistent scoring technique (single pass, correct pressure)
• Students can differentiate between a good score (thin, clean line) and a bad score (chips, white powder, incomplete)
• Students maintain wet grinding conditions throughout and understand why

Assessment Rubric

Criteria	Excellent (4)	Proficient (3)	Developing (2)	Beginning (1)
Scoring technique	Clean, single-pass scores with consistent pressure	Mostly clean scores, minor inconsistencies	Multiple passes needed, some chipping	Unable to produce consistent scores
Breaking accuracy	All breaks follow score line cleanly	Most breaks clean, 1-2 minor deviations	Several breaks deviate from score	Frequent uncontrolled breaks
Grinding quality	All edges even, accurate to template within 1mm	Edges mostly even, within 2mm of template	Uneven edges, some chips, within 3mm	Significant gouging or template mismatch
Safety compliance	Maintains wet grinding, wears safety glasses, cleans fragments properly	Minor lapses, self-corrects	Needs reminders about safety procedures	Multiple safety violations

Safety Considerations

• Safety glasses are mandatory throughout the entire activity
• Never wipe glass fragments from the work surface with bare hands — use whisk broom and dustpan
• Dispose of all glass fragments in the dedicated glass waste container (not regular trash)
• Maintain water level in grinder at all times — stop grinding immediately if water is low
• Do not force glass against the grinder bit — light pressure prevents edge chipping and bit damage
• Report any cuts immediately, no matter how minor — glass cuts are deep and contamination-prone
• Long sleeves recommended to protect forearms from glass splinters during breaking

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Last Updated: 2026-03-19