Custom Optical Fused Quartz Glass: JGS1 vs JGS2 vs JGS3 Grades, Machining, and Application Guide
When a project calls for precision optics, UV transmission, or thermal stability beyond what ordinary glass can deliver, custom optical fused quartz glass is usually the answer. Unlike sheet glass or soda-lime windows, fused quartz is manufactured from high-purity silicon dioxide (SiO2) and can be machined into windows, lenses, prisms, sight glasses, cuvettes, and furnace viewports that meet tight engineering requirements.
This guide explains how to select between the JGS1, JGS2 and JGS3 grades, what custom machining capabilities you should expect from a fabricator, and how to specify optical fused quartz parts for industrial and laboratory use.
What Is Optical Fused Quartz Glass?
Optical fused quartz glass is an amorphous form of silicon dioxide produced by melting high-purity natural or synthetic quartz at temperatures above 1700°C. The result is a glass with an extremely low coefficient of thermal expansion (about 0.55 × 10-6/°C), outstanding thermal shock resistance, and transmission from deep ultraviolet (UV) to near-infrared (IR).
In the Chinese standard system used by many fabricators, optical fused quartz is classified into three grades — JGS1, JGS2 and JGS3 — which correspond roughly to international grades such as Spectrosil, Herasil and Infrasil from other suppliers. The grade you choose depends on your wavelength range, purity requirements, and operating temperature.
JGS1 vs JGS2 vs JGS3 – Grade Selection
JGS1: UV-Grade Fused Quartz
JGS1 is synthetic (silicon-tetrachloride-derived) fused quartz with the highest purity, typically above 99.99% SiO2. It offers the best deep-UV transmission, down to 185 nm, and the lowest bubble and inclusion content. Choose JGS1 when your application needs maximum UV transmittance — for example UV lithography, UV curing lamps, spectroscopy, or ozone-generating equipment.
JGS2: General Optical Fused Quartz
JGS2 is made from natural crystal quartz. It has slightly lower purity than JGS1 but still delivers excellent transmission from roughly 220 nm to 2500 nm. It is the most common grade for general optical components, laboratory glassware, and high-temperature sight windows where deep-UV performance is not the deciding factor. JGS2 offers an attractive balance of optical quality and cost.
JGS3: IR-Grade / Low-OH Fused Quartz
JGS3 is a low-hydroxyl (low-OH) fused quartz grade optimized for infrared transmission, extending beyond 2500 nm. It is the preferred material for IR windows, thermal imaging housings, and high-temperature furnace viewports where water (OH) absorption in the glass would otherwise reduce IR throughput.
The table below summarizes the three grades:
| Grade | Raw Material | Purity | Useful Transmission | Best For |
|---|---|---|---|---|
| JGS1 | Synthetic | ≥99.99% | 185 nm – 2500 nm | Deep-UV optics, lithography, UV lamps |
| JGS2 | Natural crystal | High | 220 nm – 2500 nm | General optics, labware, sight windows |
| JGS3 | Natural crystal (low-OH) | High | 220 nm – 2800 nm+ | IR windows, furnace viewports |
Custom Machining Capabilities for Optical Quartz Glass
Off-the-shelf quartz discs are rarely enough. Most engineering projects require custom shapes, holes, threads, and surface finishes. A capable fabricator should offer the following processes:
CNC Cutting, Drilling and Grinding
CNC machining of fused quartz uses diamond tooling to cut, drill, mill and grind the material to tight tolerances. Custom quartz windows can be produced in round, square, rectangular or irregular shapes, with through-holes, counterbores, slots and stepped profiles for mounting. Because fused quartz is hard and brittle, machining must be carried out with controlled feed rates and coolant to prevent chipping. Recent advances in precision fabrication, such as the ultra-precision fabrication research at the University of Cambridge, continue to expand what is possible with fused silica micro-structuring.
Polishing and Surface Finish
Optical-grade polishing determines transmission and imaging quality. Standard finishes range from ground (matte) surfaces for furnace viewports to optically polished surfaces with roughness below 1 nm Ra for laser and imaging optics. Specify the finish you need based on whether the part is a structural window or a precision optical element.
Tolerances and Edge Treatments
Typical CNC tolerances for custom quartz parts range from ±0.05 mm to ±0.10 mm on machined dimensions, with tighter values possible for polished surfaces. Edge treatments such as beveling and edge polishing reduce stress concentration and chipping during installation, which is especially important for sight glasses under pressure and thermal cycling.
Key Optical and Thermal Properties
Custom optical quartz glass is specified for properties that ordinary glass cannot match:
- Transmission: up to 90%+ in the UV-Vis range (single-side uncoated, depending on grade and thickness)
- Continuous service temperature: 1100°C – 1200°C
- Softening point: around 1680°C
- Coefficient of thermal expansion: approximately 0.55 × 10-6/°C
- Thermal shock resistance: excellent — can be quenched from high temperature without cracking
- Dielectric strength and chemical resistance: very high, resistant to most acids (except hydrofluoric acid and hot phosphoric acid)
Typical Applications
Semiconductor and Photonics
JGS1 wafers and windows are used in semiconductor process chambers, photolithography optics, and UV exposure systems where deep-UV purity is critical.
Laboratory and Analytical Instruments
Quartz cuvettes, sample cells, and optical flats made from JGS1 or JGS2 are standard in UV-Vis spectrophotometry, fluorometry, and chemical analysis because of their optical clarity and chemical inertness. Fused quartz has a long history in scientific laboratories — the fused quartz laboratory glassware collection at the MIT Museum shows how far the material has been used in experimental chemistry.
Furnace and Lamp Windows
Fused quartz sight glasses and viewports for high-temperature furnaces, boilers, and heating lamps must withstand 1100°C+ environments while maintaining transparency. JGS2 and JGS3 are common choices for these windows, often supplied with ground edges or simple polished faces.
How to Specify Custom Optical Quartz Glass Parts
To get accurate quotes and fast turnaround, provide the fabricator with:
- Drawing or sketch with dimensions (include thickness and any holes, slots, or stepped features)
- Grade requirement (JGS1, JGS2, or JGS3) and why — especially if UV or IR transmission matters
- Surface finish (ground, polished, or both faces; specify roughness if known)
- Edge treatment (bevel, chamfer, or edge polish)
- Quantity and lead time
- Application context (temperature, pressure, wavelength) so the supplier can flag risks
A fabricator with no minimum order quantity (MOQ) and a fast prototyping service will help you validate the design with a small batch before committing to production volumes.
FAQ
Q: Can you CNC drill holes in fused quartz glass without cracking it?
A: Yes. With diamond tooling, proper coolant and controlled feed rates, holes from about 1 mm diameter upward can be drilled reliably. Edge quality depends on wall thickness and hole depth.
Q: What is the maximum continuous working temperature of optical quartz glass?
A: For long-term service, 1100°C – 1200°C is the safe range. Short-term exposure at higher temperatures is possible but depends on load, atmosphere and geometry.
Q: Does JGS1 transmit 185 nm UV light?
A: Yes. JGS1 (synthetic fused quartz) transmits from about 185 nm upward, which is why it is used for deep-UV applications. JGS2 starts transmitting effectively around 220 nm.
Q: Can quartz sight glasses be made in small batches for prototyping?
A: Yes. Suppliers with no MOQ commonly accept one-off or small-batch orders for testing and validation.
Conclusion
Custom optical fused quartz glass offers a unique combination of deep-UV transmission, thermal stability and mechanical machinability that makes it indispensable for precision optics, laboratory instruments and high-temperature equipment. Selecting the right grade — JGS1, JGS2 or JGS3 — and working with a fabricator that provides CNC machining, optical polishing and flexible batch sizes ensures your parts perform exactly as specified.
If you are designing custom optical quartz windows, sight glasses, or cuvettes, send your drawing with dimensions and grade requirements to get a tailored solution for your application. Explore our custom quartz glass tubes and components or contact us directly for a quote.