Module 4: Assessment Quiz

Module: U12M4 - Glass Engraving and Finishing Passing Score: 70%

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What type of engraving tool bit is most commonly used for glass rotary engraving?

Diamond-coated or silicon carbide burrs that abrade the glass surface

High-speed steel drill bits designed for metal cutting

Tungsten carbide router bits used in woodworking

Ceramic grinding stones designed for sharpening knives

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Explanation: Glass engraving requires abrasive materials harder than glass (Mohs 5.5-7). Diamond-coated and silicon carbide burrs are the standard choice because they abrade the glass surface cleanly without shattering it, producing controlled line work and textures.

What is the primary safety hazard unique to sandblast engraving?

High-velocity abrasive particles that cause severe skin, eye, and respiratory injury

Electrical shock from the compressor motor

Thermal burns from friction-heated glass

Chemical exposure from the sandblast media

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Explanation: Sandblasting propels abrasive particles (aluminum oxide, silicon carbide, or glass bead) at high velocity. These particles cause severe injury to exposed skin (abrasion), eyes (corneal damage), and lungs (silicosis from inhaled particles). Full PPE including blasting hood, gloves, and respiratory protection is mandatory.

What material is used to mask areas of glass that should NOT be etched during sandblasting?

Vinyl resist film or rubber stencil material that blocks the abrasive stream

Painter's tape, which peels off cleanly after blasting

Clear nail polish applied over the protected areas

Wax coating that melts away during the process

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Explanation: Vinyl resist film (self-adhesive, cut to pattern) or rubber stencil material withstands the abrasive blast stream and protects covered areas. Standard tape, paint, or wax cannot withstand the force of abrasive particles and would be destroyed almost instantly.

What acid is used for chemical glass etching, and why is it extremely hazardous?

Hydrofluoric acid (HF), which penetrates skin and causes deep tissue and bone damage

Hydrochloric acid (HCl), which dissolves glass rapidly on contact

Sulfuric acid (H₂SO₄), which generates toxic fumes when applied to glass

Acetic acid (vinegar), which slowly etches glass over several hours

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Explanation: Hydrofluoric acid (HF) is the only common acid that dissolves silica. It is extremely dangerous because it penetrates skin painlessly and causes deep tissue damage, including bone destruction (fluoride ion binds calcium). HF exposure can be fatal even from small skin contact areas. Educational settings typically use commercial etching creams (containing bifluorides) as a safer alternative.

What is fire polishing and when is it used?

Briefly heating a glass edge or surface with a torch flame to melt the surface layer smooth

Polishing glass with a heated buffing wheel coated in polishing compound

Applying a clear glaze to glass and firing it in a kiln

Rubbing glass with a hot metal tool to smooth imperfections

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Explanation: Fire polishing uses a torch flame to briefly melt the outermost surface layer of glass, which then flows smooth under surface tension. It transforms a ground or rough-cut edge into a glossy, transparent finish. The exposure must be brief — too long softens the piece and deforms it.

What determines engraving depth in sandblast carving?

Blast duration, air pressure, abrasive type, and distance from the glass surface

Only the type of abrasive media used

The thickness of the glass being engraved

The color of the glass — darker glass etches deeper

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Explanation: Sandblast depth is controlled by multiple variables: longer exposure removes more material, higher pressure increases removal rate, coarser abrasives cut faster, and closer distance concentrates the blast. Skilled operators control all four variables to achieve precise depth and detail.

Why is rotary engraving typically done with water or oil lubrication?

Lubrication reduces heat buildup, suppresses glass dust, and produces cleaner cuts

Lubrication makes the glass transparent so the engraving pattern is visible

Lubrication prevents the glass from cracking due to vibration

Lubrication is purely cosmetic — it makes the finished engraving shinier

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Explanation: Lubrication serves three functions: it cools the contact point (preventing thermal cracking), suppresses silica dust (respiratory hazard), and flushes debris from the cut (producing cleaner, more detailed engraving). Dry engraving creates more dust and risks thermal fracture.

What type of laser is most commonly used for glass engraving?

CO₂ laser, which is absorbed by glass and creates controlled surface fractures

Fiber laser, which passes through glass without interaction

UV laser, which only works on coated glass

Diode laser, which melts the glass surface to create marks

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Explanation: CO₂ lasers (10.6 micron wavelength) are strongly absorbed by glass. The laser energy creates rapid, localized thermal expansion that fractures the surface in a controlled pattern, producing a frosted appearance. The result is precise, repeatable engraving without physical contact.

What is the main risk when fire polishing a thin glass edge?

The entire piece can soften and deform if the flame exposure is too long or too hot

The glass will shatter from thermal shock

The flame will discolor the glass permanently

Fire polishing only works on borosilicate, not soda-lime

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Explanation: Fire polishing requires only brief flame contact to melt the surface layer. If the flame dwells too long or is too hot, heat conducts into the body of the piece, softening it beyond the edge. Thin pieces and narrow edges are especially vulnerable to deformation. Quick, sweeping passes are the technique.

What edge profile is produced by mechanical belt grinding with progressively finer grits?

A smooth, satin-finished edge that is safe to handle but not optically clear

A razor-sharp edge suitable for cutting

A fully transparent, polished edge identical to fire polishing

A rough, frosted edge that requires further treatment

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Explanation: Mechanical grinding through progressive grits (80 → 220 → 400 → 600) produces a smooth, satin-finished edge. It is safe to handle and aesthetically clean but not optically transparent. Achieving optical clarity requires either fire polishing or cerium oxide polishing (very fine abrasive) as a final step.

What safety precaution is specific to acid etching that does not apply to other engraving methods?

Acid-resistant gloves, face shield, and immediate access to calcium gluconate gel for HF burns

Hearing protection for the noise generated during etching

Anti-static grounding to prevent electrical discharge

UV-blocking goggles to protect from acid fluorescence

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Explanation: Hydrofluoric acid (and commercial etching creams containing bifluorides) requires acid-resistant gloves (not standard nitrile — use neoprene or butyl rubber), face shield, and calcium gluconate gel must be immediately available. Calcium gluconate neutralizes fluoride ions in tissue and is the specific antidote for HF burns.

What is the advantage of laser engraving over mechanical engraving for production work?

Laser engraving is computer-controlled, contactless, and produces identical results on every piece

Laser engraving produces deeper cuts than any mechanical method

Laser engraving works on all materials, not just glass

Laser engraving does not require any safety precautions

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Explanation: Laser engraving is driven by digital files, making it perfectly repeatable across any number of pieces. It requires no physical contact with the glass (no tool wear, no breakage risk from pressure), and produces consistent depth and detail. This makes it ideal for production runs and branding applications.