Custom High-Temperature Glass: Quartz vs Tempered Glass - A Complete Selection Guide for Industrial Applications
Choosing the right custom high-temperature glass is one of the most important engineering decisions for furnaces, boilers, laboratory equipment, and optical systems. Get it wrong, and you face cracking, thermal failure, or distorted optical performance. G1119et it right, and the glass delivers years of reliable service at extreme temperatures.
In this guide, we compare the two most common options - custom fused quartz glass and custom tempered glass - so you can select the right material for your application, understand the temperature limits, and know what to specify when you order.
What Is High-Temperature Glass?
High-temperature glass is a family of glass materials engineered to withstand sustained heat, thermal shock, and chemical attack without losing mechanical or optical integrity. Industrial grades are rated from roughly 300°C up to 1900°C depending on the material, the processing method, and the application.
The three properties that matter most are maximum continuous service temperature, thermal shock resistance, and optical clarity. Different applications weigh these factors differently - a furnace sight glass needs thermal shock resistance, while an optical component needs transmission and homogeneity.
Custom Fused Quartz Glass: Properties and Applications
Fused quartz glass (also called fused silica or quartz glass) is produced by melting high-purity natural quartz or synthetic silica at over 2000°C. The result is a material with exceptional thermal, optical, and chemical properties.
Key properties:
- Maximum service temperature: 1100°C continuous, up to 1200°C for short periods, with grades like JGS1, JGS2 and JGS3
- Thermal shock resistance: excellent - fused quartz can withstand rapid temperature changes without cracking
- Optical transmission: outstanding UV to IR transmission, from roughly 185 nm to 2500 nm
- Chemical resistance: highly resistant to acids and most chemicals at elevated temperatures
- Electrical insulation: excellent dielectric properties
Typical applications:
- Quartz glass sheets, discs and wafers for laboratory and semiconductor use
- Quartz tubes for high-temperature furnaces, lamps, and optical systems
- Optical windows and lenses for UV and IR systems
- Boats and crucibles for melting and sintering processes
Because fused quartz is difficult to machine, custom sizes, drilled holes, and polished edges must be specified precisely. JGS2 is the most common optical grade for general industrial use, offering a good balance of purity, transmission, and cost.
Custom Tempered Glass: Properties and Applications
Tempered glass (also known as toughened glass) is processed by heating glass to around 600-700°C and then rapidly cooling it. This creates compressive stress on the surface and tensile stress inside, making the glass 4-5 times stronger than standard annealed glass of the same thickness.
Key properties:
- Maximum service temperature: typically 300°C continuous for standard tempered glass
- Mechanical strength: 4-5 times stronger than annealed glass
- Thermal shock resistance: good for moderate temperature swings
- Safety: breaks into small, blunt fragments rather than sharp shards
Typical applications:
- Industrial sight glass for boilers, furnaces, and pressure equipment
- Stove and fireplace glass panels
- Round or rectangular viewports for pipelines and tanks
- Machine guards and protective windows
Tempered glass cannot be cut or drilled after tempering, so all holes, cutouts, and edge shapes must be completed before the tempering process. Common custom options include sizes from 20mm to 400mm, thicknesses from 3mm to 10mm or more, and CNC-drilled mounting holes.
Quartz Glass vs Tempered Glass: How to Choose
Use this quick comparison to narrow down your choice:
- Temperature above 300°C: choose fused quartz glass
- Temperature below 300°C with impact risk: choose tempered glass
- Optical transmission required: choose fused quartz (UV/IR) or optical grade
- High pressure or boiler sight glass: choose tempered glass for strength, or quartz for high heat
- Chemical resistance needed: choose fused quartz
For most industrial sight glass applications below 300°C, tempered glass is the practical, cost-effective choice. For laboratory, optical, semiconductor, and furnace applications above 300°C, custom quartz glass is the right material.
Custom Manufacturing Options
Whether you choose quartz or tempered glass, custom processing determines how well the part fits your equipment. At Roly IndCustom, every order can include:
- Custom sizes and tolerances based on your drawings
- Cutting to size for sheets, discs, and strips
- Edge grinding and polishing for safe handling
- CNC drilling for mounting holes and ports
- Custom shapes for viewports, windows, and panels
- Material selection guidance across quartz, tempered glass, sapphire, and glass-ceramic
- Low MOQ with small batches and prototypes welcome
How to Order Custom Glass
When you request a quote, include these details to get an accurate price and lead time:
1. Material: quartz (JGS1/JGS2/JGS3) or tempered glass
2. Dimensions: diameter or length/width, and thickness
3. Holes and cutouts: positions and diameters
4. Edge finish: ground, polished, or as-cut
5. Quantity: prototype or production volume
6. Application: furnace, boiler, optical, or laboratory use
With these details, the supplier can confirm material grade, tolerances, and processing steps - and avoid costly rework from under-specified orders.
Frequently Asked Questions
What is the maximum temperature for quartz glass?
JGS1 and JGS2 quartz glass can withstand 1100°C continuous use, with short-term exposure up to 1200°C.
What temperature can tempered glass withstand?
Standard tempered glass is rated for about 300°C continuous service.
Can tempered glass be drilled after tempering?
No. All holes and cutouts must be processed before tempering.
Is fused quartz glass transparent?
Yes. Fused quartz offers excellent transmission from deep UV (185nm) to IR (2500nm), making it ideal for optical applications.
What is the difference between quartz glass and tempered glass for sight glass?
For temperatures above 300°C, use quartz glass. For lower temperatures with mechanical impact risk, tempered glass provides higher strength at lower cost.
Ready to order custom glass?
Whatever your application - furnace sight glass, boiler viewport, optical window, or quartz labware - getting the material and processing right the first time saves weeks of lead time. Send us your drawings or dimensions, and our engineers will confirm the best material grade, tolerances, and pricing for your project.