Glass Material Explained: From Composition to Selection

Glass material is typically an amorphous solid. For a cover panel, the options include soda-lime for conventional substrates, borosilicate for low thermal expansion, and an aluminosilicate grade designed for chemical strengthening. A material name leaves much of the part undetermined.

Updated October 2026

Composition of glass: what the raw materials do

A connected network of silica forms the backbone of ordinary soda-lime glass. Soda ash aids batch melting and limestone provides calcium oxide. Raw material recipes identify batch compositions; oxide analyses identify finished glass compositions. In procurement, specifications for final glass compositions or grades should be provided rather than batch ingredient recipes.

What is the main material to make glass?

Silica sand is a principal virgin raw material for ordinary soda-lime glass. Silicon dioxide forms a connected network as the melt becomes solid. Other ingredients can also dictate behavior and control the duration of the melting process, as well as chemical stability and color. Silica is therefore a major component of glass, while the rest of the ingredients dictate the grade and its usage.

The Corning Museum of Glass demonstrates the roles of soda ash and limestone in its melting demonstration. Carbonate ingredients release gas during batch melting; weighing the raw ingredients and analyzing the finished oxide composition therefore gives different percentages.

Consider the glass network as a connected framework within which links can be rearranged by added oxides. Boron- and aluminum-containing formulations modify that network in distinct ways. A drawing marked only “clear glass” leaves those options open. For a repeat order, place the selected grade on the material requirement line alongside the drawing revision.

Glass types: soda-lime, borosilicate and aluminosilicate

Soda-lime, borosilicate, and aluminosilicate define composition families. Use soda-lime for routine glazing. Use a borosilicate grade for thermal movement control. Use an aluminosilicate grade designed for chemical strengthening for a thin cover. Different glass grades within these families differ in properties. Float glass defines a forming method and can overlap with a chemical-family description.

Soda-lime is a common type of glass for window glass and glass containers. For equipment exposed to repeated temperature changes, borosilicate material options deserve comparison because low expansion reduces free dimensional movement. Thin display covers often lead designers toward aluminosilicate glass grades selected for ion exchange.

These families are not mutually exclusive recipes. A Corning-authored paper on boro-aluminosilicate glass discusses a composition containing both boron and aluminum. Use the grade designation when the family label is too broad.

The 3-Layer Glass Choice

The 3-Layer Glass Choice differentiates substrate, strengthening (if any) or assembly, and surface finish for each layer of the selection.

SCHOTT BOROFLOAT 33 lists a mean expansion coefficient of 3.25 × 10⁻⁶/K over 20–300 °C. Pilkington Microfloat lists 9 × 10⁻⁶/K over 50–350 °C. Gorilla Glass Victus 2 lists 5.88 × 10⁻⁶/K over 0–300 °C. These are three named grades with different averaging intervals.

Imagine we have an inspection window that has a closing gap during warm-up. First, consider the temperature distribution and the expansion across the window. Substituting a strengthened display grade because it can withstand more handling damage may not solve the thermal problem. A low expansion substrate can still get chipped at a drilled hole. Keep the finished part mechanical test and thermal calculation as separate decisions.

Glass production: from molten glass to flat glass

In industrial glassmaking, a batch of material is melted, and before forming, bubbles are removed. The material is then formed and cools. Flat glass passes through a series of operations such as cutting and finishing, and finally it’s put to its end use. A glass factory that does primary glass manufacturing and a workshop that machines the finished part do different jobs.

The German glass industry association describes the production stages, including refining at roughly 1,450–1,650 °C according to composition. That furnace interval is a process condition, not a service-temperature rating for a cover panel.

1. Prepare the batch. Weigh raw materials from silo storage in the batch house; a conveyor carries the mix before it is fed into the furnace.
2. Melt and refine. Heat combines the ingredients. Refining removes gas bubbles from the molten glass; agents such as sodium chloride assist this stage.
3. Form the product. A float line forms sheet glass on molten tin; other forming machines shape bottles or glasswork. Production methods follow the required shape.
4. Anneal and inspect. Controlled cooling reduces residual stress before dimensional and visual checks.
5. Finish and pack. Glass cutting, printing and other specified operations produce parts ready for protective packing on a pallet.

As molten glass cools, its viscosity rises as it starts to solidify and form a solid without the long-range crystalline order of many ceramics. An annealing oven determines how the glass cools through the stress-sensitive region. Thickness impacts the cooling time; a thin sheet and a bulky glass object don’t undergo the same cooling cycle.

Properties of glass: heat, strength and optical performance

Compare the properties of glass in different groups: thermal movement, mechanical failure, optical behavior and chemical exposure. A scratch result describes the surface of the glass in a given test. A bending result describes the specimen and the loading method. Neither of them describes how the mounted window reacts to repeated heating and how it responds to the sustained load.

“Loading rate plays a large role in strength values.”

Load duration and peak force are related to slow crack growth. Continuously clamped panels require a different loading history from the ones that are struck once. Edge chips, holes and contact points can concentrate stress even when the broad glass surfaces seem undamaged.

A thermal expansion example

Assumed inputs: an unconstrained 300 mm strip, heated uniformly from 50 °C to 150 °C, with each grade’s published broad-range mean coefficient used as a constant. The linear expansion relation is ΔL = α × L × ΔT. For BOROFLOAT 33, the substitution is 3.25 × 10⁻⁶/K × 300 mm × 100 K ≈ 0.10 mm.

The estimate refers to the free movement of the glass, not thermal shock survival or an installation clearance. A temperature gradient or a rigid mount changes the stress state. NIST’s engineering metrology guidance explains that expansion coefficients vary with temperature; a broad-range average adds uncertainty at the target interval.

What is the melting point of glass?

Glass has no single sharp melting point; BOROFLOAT 33, for example, softens at 820 °C. Its transformation temperature is 525 °C and its annealing point is 560 °C. Each of these temperatures defines a different physical condition, and none of them indicates an operating limit of an assembled and finished product.

High temperatures also affect seals, inks and coatings. For a clear inspection panel, consider transmission at the working wavelength and thickness. Energy efficiency and thermal insulation require a separate heat-transfer assessment of the full assembly; low thermal expansion alone says little about heat loss through it.

Tempered glass, lamination and coatings

Tempered glass receives a strengthening treatment and laminated glass combines glass plies with an interlayer. A surface coating also changes a material property. These can be done in combination with an appropriate substrate; ordering “tempered” or “coated” still requires specification of a grade, thickness and some other defined performance of the completed part.

Thermal tempering achieves surface compression by rapid cooling. Chemical strengthening is possible in compatible glasses by means of ion exchange. ASTM C1422/C1422M-26 classifies chemically strengthened glasses by surface compression and depth of compression. These measures of compression should be distinguished from the bending strength.

Not all thermal toughening processes exclude borosilicate: for example, BOROFLOAT 33 provides that option. Suitability still follows the actual grade and part geometry. Finish the final machining and drilling before selecting the heat treatment that locks in those dimensions.

A laminate may use annealed plies or strengthened plies with a plastic layer, and fragment retention may be achieved with the interlayer and supports. The laminated and tempered glass comparison touches on this construction method in more detail.

Reducing the iron content in the glass also reduces its green tint. Anti-reflective coatings on the glass surface help reduce reflections, and anti-glare treatments help scatter reflected light. Anti-fingerprint treatments address fingerprint marks on the glass. A low-iron glass with an unsuitable surface treatment can still adversely affect the display.

Glass for industrial touch-screen covers

Chemically strengthened aluminosilicate is a candidate for thin covers exposed to handling. A wet operation requires the sensor and readout electronics to discern between a finger and water.

A 2019 study by Zhong and colleagues improved that distinction through electrical-field shaping. Designing such a readout circuit requires consideration for the parasitic capacitance the design introduces. Solving the sensing issue requires a different approach from choosing an easy-to-clean coating.

Example: A 300 × 200 mm indoor control panel must remain readable when illuminated from above and be operable after cleaning. Starting with a clear prototype, compare anti-glare and anti-reflective samples over a powered display. Inspect small text at the intended viewing distance and exercise the sensor through the full cover and adhesive stack rather than a loose sample held against a window. Keep the mounting and cleaning liquid the same for all samples. A cover that reduces sharp reflections may alter the image, so decide from the display assembly rather than a loose sample.

What are some applications of glass?

Display covers, inspection windows, partition walls, laboratory equipment and containers are made of glass. Each use demands different properties: a jar needs a suitable container composition, while a machine interface needs readable optics and reliable touch operation. Optical glass and glass fibers add further requirements for light transmission and shape.

In industrial applications, industrial HMI cover requirements should include the cover, sensor, bezel and adhesive in the sample build. Sharp metal contacts should be kept away from vulnerable edges. Evaluation should duplicate the intended clamping condition.

Custom glass cost: where the quote changes

The cost of custom glass includes the materials as well as the work to machine it to the final shape and dimension. This includes various edge finishes, hole drilling, strengthening, and coating. When structuring quotes, the lowest sheet price doesn’t always reflect the lowest part price. Compare quotes using the same drawing revision and acceptance plan.

The University of Georgia scientific glass shop separates labor from materials and parts in its pricing. The shop does scientific glassblowing and repair, but its separation of costs is useful for a cover glass request: identify materials, fabrication and one-time work rather than lump them together in a total.

Assuming two suppliers quote the same panel outline, one includes polished edges, drilled mounting holes, and optical inspection; the other just does the cutting. First adjust for those operations. Then ask for the same prototype and production quantities, coating spec, and packing. If an appearance limit can be relaxed outside the visible window, mark those areas of glass on the drawing. Avoid relaxing the whole surface merely to reduce a quote when part of it sits directly over the display.

After tooling or sample approval, a revision can add another fabrication cycle. Freeze the functional opening and hole locations and compare production prices.

Glass suppliers: material makers and precision fabricators

The primary role of glass works is producing the substrate; precision fabricators turn selected stock into finished parts. A buyer sourcing a composition needs grade data. A buyer sourcing a finished cover also needs shaping, edgework and treatment capability. Base the request on the work that’s required after the sheet is made.

The glass production and finishing stages described by BV Glas help distinguish the roles. At SW Glass, custom cover glass processing includes CNC shaping, strengthening options and surface treatments. Send the material choice and part drawing to SW Glass so the processing proposal addresses the finished part.

Procurement summary: match the grade to the drawing

Material specifications should travel with the drawings, sample plan, and functional acceptance criteria. Define the treatment and how the finished product will be measured. Engineering handles fit and function. Procurement aligns the quoted scope. Quality inspection verifies the approved characteristics on the shipped parts.

ASTM C1036-25 provides a basic flat glass specification. Include the appropriate material and product requirements alongside it. Copy the example specifications below and adjust the geometry to your design.

In obtaining the purchase order approvals, confirm the grade of the material, the possible processes and acceptance methods. Keep the purchase order with the signed sample and drawing revision.

Frequently asked questions