Soda-Lime Glass
Definition
The commonest glass family. About 72 percent SiO2, 14 percent Na2O (from soda ash) and 10 percent CaO (from limestone), with small amounts of MgO and Al2O3. Used in windows, bottles and tableware. Refractive index roughly 1.51 to 1.52.
- SiO2 content
- About 72%
- Na2O content
- About 14% (from soda ash)
- CaO content
- About 10% (from limestone)
- Refractive index
- About 1.51 to 1.52
- Common uses
- Windows, bottles, tableware
Common questions
Why does refractive index matter for identifying soda-lime glass fragments?+
Refractive index is measured using techniques such as the oil-immersion or GRIM method and is highly reproducible for a given glass batch. Because soda-lime glass sits within a known, fairly narrow range, RI measurement lets an examiner compare a fragment from a scene against a control sample with good discrimination.
Can soda-lime glass be distinguished from borosilicate glass on composition alone?+
Yes. Borosilicate glass contains boron oxide and much lower soda and lime content, giving it a distinctly different elemental profile and a lower refractive index and thermal expansion than soda-lime glass, which elemental analysis such as SEM-EDX can readily separate.
Does every window or bottle share an identical soda-lime composition?+
No. While the family shares the same three main oxides in roughly similar proportions, minor variation in composition and additives between manufacturing batches is what allows soda-lime glass fragments to sometimes be discriminated between different sources rather than treated as generically identical.
Related terms
- Borosilicate Glass
- Heat-resistant glass with about 80 percent SiO2 and 13 percent B2O3 (boric oxide). Low thermal expansion. Used in cookware (Borosil, Pyrex) and...
- Concentric Crack
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- Float (Pilkington) Glass
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- Laminated Glass
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- Radial Crack
- A crack that runs outward from the point of impact, like spokes of a wheel. The 3R rule applies: Radial cracks have...
- Tempered Glass
- Glass heat-treated to introduce compressive surface stresses and tensile core stresses, producing a material four to five times stronger than annealed glass...
- Wallner Lines and Hackle Marks
- Wavy curved lines (Wallner) and step-like ridges (hackle) on a fracture surface that record the direction the crack front was moving. Used...