Quartz Glass FAQ: Properties, Grades, Products, and Ordering

Quick answer

What are the most important facts about quartz glass? Quartz glass, fused quartz, and fused silica are names for the same family of amorphous, high-purity SiO₂ (≥ 99.99%). It runs continuously to 1200°C, tolerates fast temperature change because its thermal expansion is only about 5.5 × 10⁻⁷ per °C, resists most acids, and in the right grade transmits ultraviolet light that borosilicate blocks. It is attacked by HF, hot concentrated phosphoric acid, and hot strong alkalis, and it is hard but brittle.

Key takeaways

• There is no sharp melting point: fused silica softens gradually near 1680°C, with short-term use to 1300°C.
• JGS1, JGS2, and JGS3 are optical grades chosen by wavelength, not quality rankings.
• FGQuartz is a manufacturer: no minimum order, quotations typically within 24 business hours, and parts made from a drawing, sketch, sample, or description.

Written by the FGQuartz Engineering Team · Updated October 2026

Basics

What quartz glass is and how it differs from other glass

Properties

Heat, expansion, strength, chemistry, and UV

Grades and comparisons

JGS grades, clear vs opaque, quartz vs other materials

Products and sizes

Sizes and options for tubes, rods, plates, boats, crucibles, tanks

Custom fabrication

Drawings, sketches, samples, machining, and welding

Applications

Semiconductor, solar, fiber, laboratory, optics, high temperature

Care and handling

Cleaning, heating, support, and handling

Ordering

Company, quality system, MOQ, quotes, and shipping

What is quartz glass?

Quartz glass is amorphous, high-purity silicon dioxide (SiO₂) made without the soda, lime, or boron fluxes used in ordinary glass. FGQuartz supplies it at SiO₂ ≥ 99.99%. It is chosen where heat, purity, or ultraviolet transmission rule out common glass, for example in semiconductor furnaces, laboratory ware, optics, and fiber-optic preform work. It is melted above 1700°C, which is one reason it costs more than ordinary glass. See What is quartz glass? for the long explanation.

Are quartz glass, fused quartz, and fused silica the same thing?

Yes in everyday purchasing: all three names describe amorphous, high-purity SiO₂. The difference that matters is feedstock. Fused quartz is melted from natural quartz crystal and is the usual choice for tubes, boats, and crucibles. Fused silica is synthetic, usually made from SiCl₄, and is purer and more uniform optically. When you order, specify the application or grade rather than relying on the name alone.

How is quartz glass different from ordinary glass?

Quartz glass is nearly pure SiO₂, while ordinary soda-lime glass is roughly 70% SiO₂ plus soda and lime. In practice that means quartz glass runs continuously at 1200°C where soda-lime glass is limited to about 300–400°C, expands more than ten times less when heated, and, in the right grade, transmits ultraviolet light from about 185 nm. A borosilicate beaker and a quartz process tube are not interchangeable.

Is quartz glass the same as crystalline quartz or “quartz” countertops?

No. Crystalline quartz, such as the mineral or piezoelectric crystals, has an ordered structure, while quartz glass is amorphous. Kitchen “quartz” countertops are crushed stone bound with polymer and have nothing in common with fused silica.

Why is quartz glass more expensive than regular glass?

Quartz glass costs more because the feedstock is far purer, the melt is hotter than 1700°C, machining needs diamond tooling, and custom parts are made in small volumes. The price buys continuous service to 1200°C, low contamination, and UV transmission, not a commodity container. There is no single list price: cost follows geometry, grade, and quantity, so FGQuartz quotes from a drawing, sketch, or sample.

How pure is FGQuartz quartz glass?

FGQuartz quartz glass is SiO₂ ≥ 99.99%. A typical process-grade baseline is aluminum below 10 ppm, iron below 5 ppm, sodium plus potassium below 5 ppm, and total metals below 20 ppm. Trace metals and hydroxyl (OH) content vary by grade, so state any limits for your process when you request a quotation.

What temperature can quartz glass withstand?

Quartz glass runs continuously at 1200°C and for short periods up to 1300°C. Above those temperatures it sags and, if contaminated, devitrifies faster. For furnace tubes and crucibles the practical limit is usually set by sag, so wall thickness and unsupported span matter as much as the datasheet temperature. Confirm the thermal cycle with engineering for demanding jobs.

Does quartz glass have a melting point?

No, not a sharp one. Fused silica is amorphous and softens gradually, with a softening point near 1680°C, an annealing point near 1215°C, and a strain point near 1120°C. Because working temperatures sit below the softening point, quartz holds its shape in ordinary furnace service.

How well does quartz glass handle thermal shock?

Quartz glass handles rapid heating and cooling better than borosilicate glass or alumina because its thermal expansion is so low. A properly designed, annealed, supported part can go through steep temperature changes. It still pays to heat and cool at a controlled rate where possible, lift hot parts with tongs, and set them on a heat-resistant surface instead of wet or cold metal.

What is the thermal expansion of quartz glass?

The linear expansion of fused silica is about 5.5 × 10⁻⁷ per °C between 20 and 300°C. That is roughly one-sixth of borosilicate 3.3 (about 3.3 × 10⁻⁶ per °C) and more than ten times lower than soda-lime glass, which is the basis of its thermal shock resistance. Joints to metals or ceramics still need a designed transition, such as a flange, clamp, or bellows.

What are the other key physical properties of quartz glass?

Typical values for high-purity fused silica are a density of about 2.2 g/cm³, thermal conductivity of about 1.4 W/(m·K) at 20°C, a refractive index of 1.4585 at 589 nm, and a dielectric constant of 3.75 at 1 MHz. It is an excellent electrical insulator, with resistivity above 10¹⁸ Ω·cm at 20°C. See the specifications page for the complete tables.

How strong is quartz glass?

Quartz glass is hard but brittle. Typical values are Mohs hardness 5.5–6.5, compressive strength about 1100 MPa, flexural strength about 67 MPa, and tensile strength about 48 MPa. Design parts to carry load in compression, protect edges and thin walls from impact, avoid point loads, and anneal after welding or heavy machining.

Is quartz glass chemically resistant?

Yes, with exceptions. Quartz glass has excellent resistance to hydrochloric, nitric, and sulfuric acids, aqua regia, water, and organic solvents. It is attacked by hydrofluoric acid (HF), hot concentrated phosphoric acid, and hot strong alkalis such as KOH or NaOH. Mention every chemical in your first message so engineering can confirm suitability.

Can I use quartz glass with hydrofluoric acid (HF)?

No. HF dissolves fused silica, even when dilute, so quartz is the wrong material for HF service. Use PTFE, PFA, or another fluoropolymer for steps that involve HF. FGQuartz will say so rather than quote a part that will not last.

Can quartz glass hold hot alkaline solutions or molten salts?

Not safely. Hot strong alkalis attack quartz, which is why hot alkaline texturing baths and molten alkali fluxes such as NaOH or Na₂CO₃ do not suit quartz vessels. Use a crucible or bath material chosen for alkali service instead.

What is devitrification, and how do I avoid it?

Devitrification is the slow clouding of quartz glass where the surface starts to crystallize, which weakens the part. It is promoted by alkali salts and fingerprints on the surface when the part is heated above roughly 1150°C. Clean quartz with an acid bath or an alcohol wipe before heating and avoid touching working surfaces with bare hands.

Does quartz glass transmit ultraviolet light?

Yes, in the right grade. JGS1 transmits from about 185 nm, and a 10 mm path exceeds 90% at 254 nm. JGS2 is usable from about 220 nm. Borosilicate glass cuts off the deep UV, so UV lamp envelopes, photochemical cells, and deep-UV windows are made from fused silica.

What are JGS1, JGS2, and JGS3 quartz glass?

JGS1, JGS2, and JGS3 are optical grades of fused silica, separated by the wavelengths they transmit. JGS1 transmits about 185–2500 nm (deep UV), JGS2 about 220–2500 nm (UV to visible), and JGS3 about 260–3500 nm (infrared). The number is a spectrum class, not a quality ranking. See the JGS1 / JGS2 / JGS3 guide.

Which JGS grade do I need for my wavelength?

Choose by the shortest or longest wavelength your part must pass. If it must transmit below about 220 nm, specify JGS1. For general UV-to-visible windows and cuvettes, JGS2 is typical. If it must work into the infrared beyond about 2.5 µm, specify JGS3. Send the wavelength range, thickness, and surface requirement with your enquiry.

Do process tubes and wafer boats use JGS optical grades?

Usually not. Standard process tubes, wafer boats, and crucibles are made from non-optical fused quartz unless a JGS grade is specified. JGS grades matter when light has to pass through the part, such as windows, cuvettes, and flow cells.

What is the difference between clear and opaque quartz glass?

Clear quartz lets light and radiation pass, so you can see through it and use it for optical access. Opaque quartz, which contains fine closed bubbles, scatters light and works as a thermal liner or heat shield. Choose clear when you need to observe or transmit light, and opaque when you want insulation or radiation shielding.

Quartz glass or borosilicate glass: which should I use?

Use borosilicate for ordinary laboratory ware up to about 500°C. Choose quartz glass when you need continuous service above that, UV transmission below about 300 nm, very low contamination, or flame-welded custom geometry. Quartz costs more and is machined only with diamond tools. See quartz vs borosilicate glass for a full comparison.

How does quartz glass compare with alumina ceramic?

Alumina (99.7%) tolerates higher continuous temperatures, about 1600°C or more, but it is opaque, cannot be flame-welded, and has limited thermal shock resistance. Quartz glass tops out near 1200°C continuous but is transparent in the right grade, handles fast temperature change, and can be welded and formed. Pick by the temperature, visibility, and shock your process involves.

What quartz glass products does FGQuartz make?

FGQuartz makes seven standard product lines in fused silica: tubes, rods, plates and windows, wafer boats, crucibles, tanks, and inline heaters. Anything else is built as custom quartz glass.

What sizes of quartz glass tube can FGQuartz make?

FGQuartz makes quartz tubes from 5 mm to 1000 mm outside diameter, with walls from 0.5 mm to 20 mm or more, in lengths up to 3000 mm (longer by welded sections). There is no fixed stock chart: tubes are made to your drawing, and these ranges are typical examples rather than limits. Send OD and wall (or OD and ID), length, and end details.

Can quartz tubes be flanged, ported, bent, or sealed?

Yes. Tubes can be fitted with fused or CNC-machined flanges (including O-ring faces), external or internal threads, side ports and manifolds, flame-formed bends, and sealed ends that are domed or flat. Multi-part welded assemblies are annealed after hot work. Send the process gas, temperature, and a drawing or sketch so ports and welds can be planned.

What pressure can a quartz tube withstand?

There is no catalogue pressure rating, because quartz is much stronger in compression than in tension. The rating depends on wall thickness, outside diameter, length, and surface condition, and it is calculated per drawing. Give your working pressure, temperature, and cycle when you enquire, and engineering will recommend a wall or flag an unsafe design.

What diameters of quartz rod are available?

Quartz rods are typically made from 3 mm to 300 mm in diameter. They can be centerless-ground for tight diameter control, drilled, grooved, threaded, or end-polished, and are used as supports, fiber preform starting rods, stirring rods, and fixtures. Centerless-ground rods typically reach straightness and concentricity better than 0.1 mm per meter.

What size and flatness can quartz plates and windows have?

Quartz plates are typically 0.5–50 mm thick and up to 1200 × 1200 mm. Optical-grade plates can reach flatness down to λ/10 with parallelism under 30 arc seconds, and are made in JGS1, JGS2, or JGS3 to match the wavelength. Plates can be drilled, slotted, stepped, or cut to shape. Put the optical specification on the drawing so the polishing route is quoted correctly.

What is a quartz wafer boat?

A quartz wafer boat is a fused-silica carrier with precision-machined slots that holds wafers upright in diffusion, oxidation, LPCVD, and annealing furnaces. FGQuartz makes boats for wafers from 2 to 12 inches and for solar formats such as M10 and G12, typically with 25 to 150 or more slots. Slot count, pitch, groove profile, and wafer diameter can all be customized.

Quartz wafer boat or silicon carbide boat: which should I choose?

Choose a quartz boat for standard silicon diffusion, oxidation, and LPCVD up to 1200°C where metallic contamination must stay very low. Silicon carbide suits hotter or more mechanically demanding processes. They are different material systems, so send the boat drawing or a sample rather than assuming a geometry transfers directly.

What are fused quartz crucibles used for?

Fused quartz crucibles hold molten silicon in Czochralski (CZ) and directional-solidification crystal growth, and serve as clean laboratory vessels for ashing, calcination, and trace analysis. FGQuartz makes crucibles from 10 ml laboratory sizes up to 32-inch CZ crucibles, with custom shapes, lids, and spouts available.

How is a quartz crucible priced?

There is no list price, because a 50 ml laboratory crucible and a large CZ crucible are different products. Price follows diameter, wall thickness, clear or opaque material, purity limits, tooling, and quantity. To get a number, send inside and outside diameter, height, wall, bottom type, grade, quantity, and destination. A prototype quantity can be one piece.

What are quartz tanks and inline heaters used for?

Quartz tanks are welded fused-silica baths for wet benches and chemical processing, and quartz inline heaters are flow-through chambers that heat DI water and high-purity chemicals with no metal in contact with the liquid. Both suit chemistries that quartz tolerates, such as hot mineral acids, and neither is suitable for HF, hot concentrated phosphoric acid, or hot strong alkalis. Custom volumes, ports, and flanges are specified on the drawing.

Can FGQuartz make a quartz part that is not in the catalogue?

Yes, in most cases. FGQuartz builds fused silica parts in any geometry that can be formed or machined from fused silica, and confirms feasibility in design-for-manufacture (DFM) review before quoting. The routes are a standard item, a modified standard item, or a part built from your drawing, sketch, sample, or description. See custom quartz glass.

Do I need a drawing to order a custom quartz part?

No. A dimensioned sketch, photos with key dimensions, a worn sample, or a plain description of what the part must do is enough to start. Tell us the process, temperature, chemistry, and space limits, and engineering will work out a buildable design with you. A CAD drawing speeds up quoting but is not required.

What file formats does FGQuartz accept?

FGQuartz accepts DXF, STEP, IGES, and PDF drawings, as well as dimensioned sketches and photos. Drawings in any language are fine, and dimensions in millimeters are preferred. If you only have a part, send the part or photos with key dimensions and its intended use.

Can FGQuartz copy an old or discontinued quartz part?

Yes. FGQuartz can reproduce worn, broken, or discontinued parts from a sample, or from photos with key dimensions. Tell us what the part is used for so wall thickness, ends, finish, and annealing can be matched to the job.

What can be machined or welded in quartz glass?

Quartz is machined with diamond tooling: cutting, core drilling, slotting, grooving, milling, threading, centerless grinding, and polishing. Hot work uses an oxy-hydrogen flame for forming, bending, necking, sealing, and welding flanges, ports, and multi-part assemblies. Parts are annealed afterwards to relieve stress. Quartz does not solder or weld like metal, so geometry must allow torch access, which DFM review checks.

Can FGQuartz make labware with standard ground joints?

Yes. Quartz labware can be made with standard ground joints, for example 14/20, 19/22, 24/40, and 29/42. Matched sets of beakers, flasks, crucibles, and lids can be made to one specification.

Is my design information kept confidential?

Yes. NDA protection is available before drawing submission for customers who require it.

Why is quartz glass used in semiconductor manufacturing?

Quartz glass is widely used in front-end semiconductor processing because it combines 1200°C service, low metallic contamination, and thermal cycling stability. Typical parts are diffusion, oxidation, and LPCVD process tubes, wafer boats, injectors, liners, and wet-bench tanks and heaters. HF steps need a different material. See semiconductor quartz glass.

What quartz parts are used in solar cell manufacturing?

Solar lines use quartz crucibles for CZ and directional-solidification crystal growth, diffusion process tubes, and wafer boats for M10, G12, and other formats. Quartz is not used in hot alkaline texturing baths. See solar photovoltaic quartz.

What quartz parts are used in fiber-optic preform manufacturing?

Fiber-optic work uses substrate tubes for MCVD, starting rods for VAD and OVD, and jacketing or overcladding tubes. Concentricity and wall uniformity matter most, because they affect refractive index control and preform yield. See fiber optic quartz.

Which quartz parts do laboratories use?

Laboratories use quartz crucibles, boats, beakers, flasks, reaction and combustion tubes, cuvettes, and custom apparatus for ashing, trace-element preparation, acid digestion, UV spectroscopy, and high-temperature synthesis. Quartz is not suitable where HF is present. See laboratory quartz.

Which quartz parts are used in high-temperature industrial equipment?

Industrial heating uses quartz furnace tubes and liners, infrared heater envelopes, thermocouple sheaths, and observation windows. They are chosen for continuous service to 1200°C, electrical insulation, optical access, and thermal shock resistance. See high-temperature quartz.

Which quartz parts are used in optical and laser systems?

Optical systems use windows, plates, cuvettes, flow cells, and rods in JGS1, JGS2, or JGS3, chosen by the working wavelength. Flatness, parallelism, and surface quality are set on the drawing. See optical quartz glass.

How do I clean quartz glassware before use?

Wipe quartz with alcohol or soak it in an acid bath, then rinse. Cleaning matters most before high-temperature use, because alkali salts and fingerprints encourage devitrification above roughly 1150°C. Do not use HF, hot concentrated phosphoric acid, or hot strong alkaline cleaners.

How should I heat, cool, and support quartz parts?

Heat and cool at a controlled rate where you can, even though quartz tolerates fast temperature change. Support large-diameter or thin-wall tubes along their length, lift hot parts with tongs that do not chip the rim, and set them on a heat-resistant surface instead of wet or cold metal.

Why do rims and thin walls chip, and how do I prevent it?

Quartz is hard but brittle, so edges and thin walls are the first to chip under impact or point loads. Avoid knocks, keep parts separated in storage and transport, and ask for chamfered or fire-polished edges on parts that will be handled often.

Who is FGQuartz?

FGQuartz is a quartz glass manufacturer founded in 2005 in Lianyungang, Jiangsu, China. It operates a 15,000 m² plant where melting, diamond machining, flame forming, polishing, and annealing take place on one site. It serves more than 500 customers in over 40 countries across semiconductor, solar, optics, fiber optic, laboratory, and high-temperature industries. See About FGQuartz.

Is FGQuartz a manufacturer or a trading company?

FGQuartz is a manufacturer. Material is formed, machined, and finished on its own site, so technical questions are answered by the people who make the parts.

Does FGQuartz have a quality system?

Yes. FGQuartz operates under an ISO 9001 quality system, and parts are checked against the agreed drawing dimensions before packing and shipment.

Is there a minimum order quantity?

No. FGQuartz has no minimum order quantity, so a single prototype or replacement part is a normal order. Many customers prototype one piece first and repeat or scale once it works.

How do I request a quotation, and how fast is the reply?

Send your enquiry through the contact page or by email, and engineering typically replies with feedback and a quotation within 24 business hours. Include a drawing, sketch, photo, or sample, plus the application, temperature, chemistry, and quantity if you know them.

What information should I include in an enquiry?

Useful details are what the part is for, a drawing or sketch or the old part, operating temperature, the chemicals or gases involved, size limits, finish or optical grade, quantity, and destination. None is mandatory: an incomplete enquiry is still welcome, and the team will ask for what is missing.

What are the lead times?

Simpler parts typically take 7–14 days and complex assemblies 3–6 weeks. Lead time depends on size, grade, and drawing complexity, and the quotation confirms the schedule.

Does FGQuartz ship internationally?

Yes. FGQuartz supplies customers in more than 40 countries, and parts are packed for export at Lianyungang. Production time and transit are quoted with the order, and single-piece prototypes are accepted.

Which industries does FGQuartz serve?

FGQuartz serves semiconductor, solar photovoltaic, optics and photonics, fiber optic, laboratory and scientific, and high-temperature industrial customers. See applications by industry.

What is quartz glass?

The long-form explainer on naming, structure, and uses.

Quartz vs borosilicate glass

When quartz is worth the extra cost.

JGS1, JGS2, JGS3

Pick the optical grade by wavelength.

Technical specifications

Full property tables.