Unit 12 Comprehensive Quiz: Glass Working

Unit: 12 - Glass Working Duration: 30-45 minutes Passing Score: 70% Format: Multiple choice covering all modules Questions: 12

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Instructions

This comprehensive quiz covers all modules in the Glass Working unit. You should complete all module assessments before attempting this unit quiz. The quiz tests both factual recall and application of concepts across modules.

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A student wants to create a glass piece combining lampworked borosilicate decorative elements fused onto a Bullseye COE 90 base plate in the kiln. What will happen?

The pieces will fuse successfully because all glass is compatible when heated high enough

The borosilicate elements will melt before the soda-lime base, causing them to flatten and lose detail

The piece will crack during cooling or annealing because borosilicate (COE 33) and soda-lime (COE 90) contract at vastly different rates, creating irreconcilable stress at every joint

The pieces will bond but the colors will change unpredictably due to chemical interaction

Submit

Explanation: COE compatibility is a non-negotiable rule in glass work. Borosilicate (COE 33) contracts roughly one-third as much per degree as soda-lime (COE 90). When the fused piece cools, the COE 90 base shrinks dramatically more than the borosilicate elements bonded to it. This differential creates tension at every interface that far exceeds glass's tensile strength (~7,000 PSI for soda-lime), guaranteeing fracture — sometimes during the annealing cycle, sometimes hours or days later. Always verify COE compatibility before combining any glass types in a single piece.

You are inspecting a hot shop after the previous class and notice several glass rods sitting on the workbench near the lampworking station. They show no color change or visible glow. Is it safe to pick them up with bare hands?

Yes — glass that is not glowing is at room temperature and safe to handle

Yes — as long as you touch them briefly to test, you can assess if they are hot

No — glass does not visibly glow until approximately 1000°F, meaning rods at 500-900°F (hot enough to cause instant third-degree burns) appear identical to room-temperature glass; always use tongs or check the designated cooling area log first

No — but only because glass rods may have sharp edges, not because of heat

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Explanation: This is the single most dangerous property of hot glass and the leading cause of glass burns: glass does not emit visible light (incandescence) until it reaches roughly 1000°F (540°C). A rod at 800°F — hot enough to cause full-thickness burns on contact — looks completely indistinguishable from a room-temperature rod. Standard protocol: (1) treat ALL glass near heat sources as potentially hot, (2) never touch glass with bare hands unless it has been in a verified cooling area long enough to reach ambient temperature, (3) use tongs or IR thermometer to verify. "Touch testing" causes burns — by the time you feel the heat, tissue damage has already occurred.

A student is grinding the edges of soda-lime glass pieces for a stained glass project. The grinder's water reservoir is empty, but the student wants to finish quickly and continues grinding dry. What hazards does this create?

The only risk is that the glass edges will not be as smooth

Dry grinding will overheat the motor and damage the equipment

Dry grinding produces airborne silica dust that causes silicosis (irreversible lung fibrosis) with chronic exposure, and the localized heat from friction without water cooling can cause thermal cracking of the glass piece

Dry grinding is acceptable for short periods as long as the student wears safety glasses

Submit

Explanation: Wet grinding is mandatory for two critical reasons. First, grinding glass produces fine respirable silica particles (< 10 microns). Silicosis is a progressive, incurable lung disease caused by cumulative silica dust inhalation — it has a 10-20 year latency period with no acute symptoms, making it a silent hazard that students often underestimate. Second, water cools the contact point between the grinding wheel and glass; without it, localized thermal stress can crack the workpiece unpredictably. If the water reservoir is empty, stop grinding immediately and refill. Per OSHA standard 29 CFR 1910.1053, the permissible exposure limit for respirable crystalline silica is 50 micrograms per cubic meter — dry grinding easily exceeds this in minutes.

A student's kiln-fused glass piece came out with a white, scaly, hazy film on the top surface, but the bottom surface is clear and glossy. The piece was held at 1250°F for 45 minutes during the ramp-up before reaching the fusing temperature of 1480°F. What caused the defect?

The kiln wash migrated to the top surface during firing

The glass was contaminated with incompatible glass chips

Devitrification — the piece spent too long in the critical devitrification zone (1100-1400°F), allowing crystal nucleation on the exposed top surface; the bottom was protected by contact with the kiln shelf

The glass was over-fired and began to boil, creating surface bubbles

Submit

Explanation: Devitrification occurs when glass lingers in its crystallization zone (roughly 1100-1400°F for most soda-lime art glass). A 45-minute hold at 1250°F — right in the middle of this zone — gave the glass surface ample time to begin crystallizing. The top surface was exposed to the kiln atmosphere and developed the characteristic white, scaly devitrification layer. The bottom surface, pressed against the kiln shelf, was shielded from nucleation. Prevention: ramp through the devitrification zone steadily at 300-500°F/hour without holding, ensure glass surfaces are clean (fingerprints and contaminants act as crystal nucleation sites), and apply a devitrification spray (borax-based) to exposed surfaces before firing.

When scoring sheet glass for a stained glass panel, a student makes a second pass with the glass cutter over the same score line because the first pass "didn't feel deep enough." What is the consequence?

The second pass deepens the score and produces a cleaner break

The second pass has no effect — the cutter simply follows the existing groove

Re-scoring crushes and chips the glass along the original fracture line, destroying the clean stress concentration needed for a controlled break — the piece will break unevenly or shatter instead of following the score

The second pass is fine for thick glass but unnecessary for thin glass

Submit

Explanation: A glass score is not a groove — it is a controlled surface fracture approximately 0.1mm deep. The first pass creates a clean, sharp crack tip that concentrates stress along the intended break line. A second pass drives the cutter wheel through already-fractured glass, crushing the edges, creating chips, and producing multiple competing fracture paths. When breaking force is applied, the crack wanders between these paths instead of following a single clean line. The result is an uneven, chipped break that requires excessive grinding to clean up. Rule: score once with firm, consistent pressure, then break immediately while the stress concentration is fresh.

A student is setting up for flameworking and grabs standard ANSI Z87.1 polycarbonate safety glasses from the PPE shelf. Their instructor stops them. Why are standard safety glasses inadequate for torch glass work?

Standard safety glasses are not impact-rated for glass fragments

Standard safety glasses fog up from the heat of the torch

Standard safety glasses do not filter the intense sodium-yellow flare (589nm) emitted by hot glass or the infrared radiation that causes cumulative eye damage — didymium or AUR-92 filtered lenses are required to both see the glass clearly and protect against IR-induced cataracts

Standard safety glasses block too much light, making it impossible to see the flame

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Explanation: Hot glass emits an intense sodium-yellow flare at 589nm that overwhelms the view of the glass shape, making it impossible to see detail while working. Standard safety glasses transmit this wavelength freely. Didymium lenses filter the 589nm sodium flare specifically, revealing the true form of the molten glass. AUR-92 lenses go further by also filtering infrared (IR) radiation in the 700-2000nm range. Chronic IR exposure causes "glassblower's cataract" — a progressive, irreversible clouding of the lens. Standard Z87.1 polycarbonate safety glasses provide impact protection but zero IR filtration. This is specialized PPE that cannot be substituted with general-purpose safety glasses.

A student is designing a kiln fusing project and wants to layer three pieces of Bullseye COE 90 glass (each 3mm thick) into a 9mm-thick fused piece. Compared to a standard single-layer (3mm) fusing schedule, what adjustments must be made to the firing program?

No changes needed — the kiln controller automatically adjusts for thickness

Only the peak temperature needs to be increased to fully fuse three layers

The annealing soak time must be significantly increased (roughly tripled) and the cooling rate through the strain point must be much slower — thick glass retains heat in the center longer, and inadequate annealing will cause delayed stress cracking from the center outward

The ramp rate should be faster to minimize devitrification since there is more glass mass

Submit

Explanation: Glass thickness is the primary variable in annealing schedules. The rule of thumb: anneal for 1 hour per 6mm of thickness at the annealing point, then cool no faster than 50°F/hour through the strain point. A 9mm piece needs roughly 1.5 hours of annealing soak (vs. 30 minutes for 3mm) and a cooling rate of approximately 40-50°F/hour through the critical range. The ramp-up rate should also be slower (200-300°F/hour vs. 400-500°F/hour) to avoid thermal shock in the thicker mass. Underestimating annealing time is the most common cause of delayed failure in multi-layer fused pieces — cracks radiating from the center that appear hours or days after the piece exits the kiln.

A student notices air bubbles trapped between two layers of glass in their fused piece after it came out of the kiln. The firing schedule ramped directly from room temperature to full fuse temperature (1480°F) at 500°F/hour. What step was missing from the firing schedule?

A pre-heat hold at 300°F to drive off surface moisture

A post-fuse hold at 1600°F to allow bubbles to rise to the surface

A bubble squeeze hold at approximately 1350-1400°F — this intermediate temperature softens the glass enough for trapped air to escape at the edges before the pieces reach full fuse temperature and seal together permanently

A slower ramp rate of 100°F/hour, which would have prevented bubbles from forming

Submit

Explanation: When two pieces of glass are stacked for fusing, air is trapped between them. As the glass softens, it begins to seal at the edges first. A bubble squeeze segment holds the temperature at 1350-1400°F (below full fuse but above the point where the glass becomes tacky) for 10-30 minutes. At this temperature, the glass is soft enough to allow trapped air to migrate to the edges and escape, but not so soft that the layers have fully merged and sealed. Once the hold is complete, the schedule ramps to full fuse temperature where the layers merge completely. Skipping this step produces permanently trapped bubbles that cannot be fixed without re-cutting and re-firing.

A student wants to sandblast a deep-carved design into a glass vase. They apply standard painter's masking tape as a resist over the areas they want to protect. What will happen?

The painter's tape will work fine for shallow etching but peel off during deep carving

The painter's tape will leave adhesive residue that ruins the glass surface

The abrasive blast will shred through the painter's tape almost immediately — sandblasting requires vinyl resist film or rubber stencil material rated for abrasive blast resistance; standard tape provides essentially zero protection

The painter's tape will melt from the heat generated by the sandblasting process

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Explanation: Sandblasting propels abrasive particles (aluminum oxide, silicon carbide, or glass bead) at velocities that quickly destroy any material not specifically designed to resist them. Painter's tape is designed to resist paint, not high-velocity abrasive impact — it will be perforated within seconds, allowing the blast to etch areas that should be protected. Proper sandblast resist is either self-adhesive vinyl film (cut to pattern with a vinyl cutter or by hand) or rubber stencil sheet material. For deep carving, thicker resist material is needed because even vinyl film wears through with prolonged blast exposure. Multiple resist layers or photoresist film is used for the deepest carvings.

After fire polishing the cut edge of a small soda-lime glass bowl, the student notices the rim has become wavy and uneven — the bowl's circular shape is distorted. What went wrong?

The torch flame was too cold, causing uneven heating

The glass was the wrong type for fire polishing — only borosilicate can be fire polished

The flame exposure was too long or too hot — heat conducted past the edge into the body of the piece, softening the thin rim enough for gravity and surface tension to deform it; fire polishing requires brief, sweeping passes to melt only the outermost surface layer

The bowl was not properly annealed before fire polishing, causing it to warp

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Explanation: Fire polishing works by briefly melting the outermost surface layer of glass (approximately 0.1mm deep), which then flows smooth under surface tension and resolidifies. The key word is "briefly" — the flame must heat only the surface, not the bulk of the glass. If the torch dwells too long or is held too close, heat conducts into the body of the piece. Thin areas like bowl rims are especially vulnerable because there is less mass to absorb heat before the entire cross-section softens. The correct technique is rapid, sweeping passes with the torch, allowing each area to cool between passes. After fire polishing, the piece should be re-annealed to relieve stress introduced by the localized heating.

A CO₂ laser engraver is available in the lab. A student wants to laser-engrave a design onto a borosilicate glass beaker. Compared to engraving soda-lime glass, what additional consideration applies?

CO₂ lasers cannot engrave borosilicate glass at all — the beam passes through it

Borosilicate requires higher laser power because it has a higher melting point

Borosilicate's low coefficient of thermal expansion (COE 33 vs. COE 90 for soda-lime) makes it more resistant to the localized thermal fracturing that creates laser engraving marks — settings must be adjusted (typically higher power, slower speed) to achieve equivalent marking depth, and results may be less consistent

Borosilicate produces toxic boron fumes during laser engraving that require special ventilation

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Explanation: CO₂ laser engraving on glass works by creating controlled micro-fractures through rapid, localized thermal expansion. The laser heats a tiny spot, causing it to expand faster than the surrounding glass, which fractures the surface. Soda-lime glass (COE 90) expands nearly three times more per degree than borosilicate (COE 33), so the same laser pulse creates significantly more thermal stress in soda-lime — making it easier to engrave. Borosilicate's thermal shock resistance, which is an advantage in torch work, becomes a disadvantage in laser engraving because the glass resists the localized thermal stress that produces the engraved mark. Power and speed settings must be adjusted, and test cuts on scrap are essential.

A student completes a stained glass panel using the copper foil method. Two weeks later, several solder joints have cracked and pieces are loose. The student reports that they soldered the joints immediately after grinding, without any intermediate steps. What was the most likely cause of joint failure?

The solder was the wrong alloy — lead-free solder should have been used

The soldering iron temperature was too low, producing cold joints

The glass edges were not cleaned and dried after grinding — residual grinding slurry and moisture prevented the copper foil adhesive from bonding properly, causing the foil to peel away from the glass under the stress of handling, which detached the solder joints from the glass

The copper foil was too narrow for the glass thickness used

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Explanation: Copper foil adhesive requires a clean, dry, oil-free glass surface to bond. Grinding produces a wet slurry of glass particles and water that coats the edges. If foil is applied directly over this residue, the adhesive never contacts clean glass — it bonds to the slurry layer, which is weak and eventually flakes off. The correct sequence is: grind, rinse thoroughly, dry completely (including crevices in textured glass), then apply foil with firm burnishing pressure. Additionally, fingerprint oils from handling ground edges can prevent adhesion. Many professionals wipe edges with isopropyl alcohol before foiling. The solder joints themselves may have been perfectly executed, but they failed because the foil underneath lost adhesion to the glass.

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Last Updated: 2026-03-19