Category Archive: Optical Glass

What is Optical Glass?

The optical industry encompasses a wide range of applications that relate to the properties and motion of light. From lenses for eyeglasses and cameras to fiber optics, optical solutions are a constant part of daily life. Optical glass is a fundamental material used in many optical applications, including prisms, lasers, beam splitters, and other optical components.

Optical Glass Properties

While it shares many of the characteristics of other types of glass, optical glass is manufactured using different chemicals to enhance properties that are useful specifically for optics applications.

Chemical Properties

Optical glass may contain a variety of additives, such as boric oxide, lead, zinc oxide, fluorite, and barium oxide to enhance its ability to transmit light within certain wavelengths. Depending on the chemical composition of the glass, different wavelengths of light, both visible and invisible, can be absorbed, transmitted, or refracted to achieve the desirable optical effect for a given application.

The two most common types of optical glass are flint glass and crown glass. Flint glass is produced using lead, while crown glass contains a higher level of potassium oxide.

Mechanical Properties

Optical glass is valued for its transparency, purity, and hardness compared to other types of glass. Optical glass is manufactured to be particularly dense, with a density up to 6.19 g/cm³. Flint glass tends to be denser than crown glass due to the inclusion of lead in its overall composition.

Optical Properties

When considering the particular optical properties of optical glass, engineers refer to the refractive index and the Abbe value. The Abbe number, VD, of a material is defined as:


where nC, nD and nF are the refractive indices of the material at the wavelengths of the Fraunhofer C, D1, and F spectral lines.

The refractive index measures the amount that light slows and bends, or is refracted, when it passes through a material. The higher the refractive index, the more refraction occurs. Flint glass, for example, has a lower refractive index than crown glass, which means that the light bends more when it passes through flint glass.

The Abbe value of a material measures the chromatic dispersion of light as it passes through the material. Depending on the material, different wavelengths of light may pass through at different speeds. The Abbe value quantifies the amount of chromatic distortion that occurs for a given material. For instance, crown glass has a higher Abbe value than flint glass, so it exhibits less chromatic distortion.

Applications of Optical Flat Glasses

Due to its exceptional level of clarity and durability, optical glass is the most commonly used material for a wide variety of optical applications, including:

  • Lenses for analytical and medical equipment
  • Photographic lenses
  • Windows for optical systems and instruments
  • Glass substrates
  • Lead radiation glasses
  • Precision lenses
  • Pressure sensors
  • Laser systems
  • Beam splitters

Advances in Optical Glass

As technology evolves, demand for high-quality optical glass for use in technology continues to increase. Its exceptional clarity and precision, coupled with high chemical and temperature resistance, make optical glass the ideal material for advanced technological applications, including robotics, virtual reality displays, laser equipment, and 3D printing. Market forecasts indicate that optical glass will see increasing demand as developers continue to explore its uses in new and improved technologies.

Our Expertise with Optical Glass

Since 1970, Swift Glass has been a reliable manufacturer of optical glass for customers around the world. Our state-of-the-art facilities provide full-service fabrication of precision optical components at high volumes and short lead times. We offer a range of value-added services to ensure that your optical glass product is exactly what you need. These services include:

  • CNC milling hand polishing
  • Precise pencil grinding
  • Flat polish
  • Crystal and ceramic lapping and polishing
  • Surface coating
  • Large plate lapping and polishing
  • Metallizing
  • Waterjet cutting
  • Assorted filter colors

For almost a century, Swift Glass has been a premier provider of glass products for a wide range of industries. Our company is ISO 9001:2015 certified and ITAR compliant to ensure the highest quality optical glass solutions for our customers around the world. With over 50 years of specialized experience manufacturing optical glass, we have the knowledge necessary to produce superior optical products consistent with the most detailed and stringent specifications.

To learn more about our exceptional optical glass products and services, contact us today or request a quote.

Understanding Optical Glass Surface Specifications

To ensure the manufacture of consistently high-quality, high-performance glass components and products, it’s critical to utilize optical specifications. These are useful in two ways: First, they establish an acceptable standard by which a glass surface must perform; second, they can help determine the amount of time, money, and labor that should be spent on the manufacturing process.

Also make sure the tolerance specifications for your project are just right. For example, if your tolerances are underspecified for a project that requires microscopic precision, the glass component may not be able to perform key tasks. If the tolerances are overspecified, this can needlessly raise the cost of production per unit or overcomplicate the entire project.

In this guide, we’ll discuss the specifications that determine the production of optical glass parts, how to look for the right specifications, and how tight tolerances should be in different circumstances.


Specialty glass such as optical components requires precisely detailed specifications so that fabricators can create parts that perform to exacting standards, with little room for error. A skilled optical glass fabricator can customize the following properties to achieve certain specifications and tolerances.

Surface Quality

Surface quality, or surface roughness, refers to how much an optical glass surface deviates from an ideal. Poor surface quality can cause unwanted light scattering in applications that require particular system wavelengths. Scratch-dig specifications—defined as the presence of scratches, bubbles, or pits—should be about 40-20 in most optical applications. At the same time, it’s important to understand the full context of the application to avoid overspecification and the added costs associated with it.

The requirements for surface quality are as varied as the applications for glass surfaces. For instance, in industrial settings, the bar set for surface quality is not as high as it would be for work with lasers. Surface quality refers solely to the cosmetic quality of a glass surface — whether it has any marks, divots, scratches, and so on. While such imperfections may not necessarily impact performance, it’s still important to consider how long-term effects, such as general wear and tear, may impact the appearance and overall quality of the glass.

Surface quality is reflected by two numbers: the scratch number, which is determined by comparing scratches on a surface to a set of standard scratches under controlled lighting conditions, and the dig number, which is calculated at the diameter of the dig in microns divided by 10. For example, 60-40 reflects precision quality, and is a common surface quality value in research and industrial sectors. The lower the number, the higher the quality of the product. Industries and applications working with lasers aim for a higher standard of 10-5.

MIL-O-13830A and MIL-O-13830B standards are the most commonly applied for surface quality, but there’s also a more complex standard, ISO 10110, which allows designers some level of control and eliminates much of the guesswork for inspectors.

Surface Flatness

Surface flatness is the measure of how flat a surface is; this test is critical for glass products such as windows, mirrors, and plano-lens. The surface flatness test accounts for surface deviations such as ripples, bows, and other imperfections, which are measured in waves — the multiple of the wavelength from the reference surface. In this case, the higher the digit, the more precise the product. To determine surface flatness, the surface being tested is compared to a high-quality, highly precise flat reference product — referred to as an optical flat — and examined for deviations by comparing the two surfaces.

To compare the surface, the optical surface at hand is placed against the optical flat. When they are placed against each other, fringes — more specifically, “Newton’s fringes” — will appear, and the shape of these fringes will determine the flatness. Evenly spaced, straight, and parallel fringes indicate that the surface being tested is at least as flat as the optical flat. Curved fringes indicate subpar glass flatness.

Having the correct surface flatness reduces the risk of scattering light that can obfuscate results or create low-quality outcomes. However, over prioritizing an exact surface flatness can increase production costs and lengthen timelines. Carefully balance the importance of the surface flatness specification with your end use component needs, budget and turnaround requirements.


This specification applies to curved optical surfaces — surfaces with power — and is tested similarly to flatness; the curved surface is stacked against a reference surface, a highly calibrated reference gauge. The air gaps created by the interference provide information on the deviation between the surfaces of the test model and the reference model. The deviations create a series of rings, referred to as Newton’s rings. The more there are, the more pronounced the deviation from the reference model.

Depending on the optical glass fabricator and intended end use, a wide array of tolerances can be possible. For general-purpose goods, a radius of curvature within 0.5% is sufficient. More precise applications may require radii with 0.1%, while some niche fabricators may offer tolerances of 0.01% for highly specialized applications.


The irregularity specification is used to describe the deviation of a test surface’s shape from the shape of its corresponding reference surface. The measurement is obtained using the same test conducted for power, but this test focuses on the sphericity of the circular fringes, which are determined by comparing the test and reference surfaces. Still, irregularity is often described as a ratio to power. For example, if the power of a surface is more than five fringes, detecting smaller irregularities (less than one fringe) is often difficult; therefore, the irregularity is reflected through this ratio of power to irregularity. In this particular example, the ratio would be 5:1.

When components deviate from the exact dimensions and surface qualities of the reference model, the optical glass can produce varying results. Determine to what degree irregularities in the circular fringes of your component matter to the outcome so you can properly weigh cost and speed against tolerance precision.

Surface Finish

Surface Lapping for the Medical IndustryDuring polishing processes, there’s always a risk of small irregularities occurring on the surface of the glass. Surface finish testing, or surface roughness testing, is used to measure these irregularities at the end stage of product manufacturing. Tolerances for surface-finish quality range from 50Å RMS, which represents typical quality, to 20Å RMS, which represents precision quality, and 5Å RMS, representing high quality.

This test will have varying degrees of importance depending on the eventual application of the glass product at hand. Surfaces intended for use in lasers and intense heat would demand a much higher surface finish than applications that don’t require the same level of precision or are less concerned with the inevitable wear that occurs in rougher surfaces.

Ensuring that surface finish meets the minimum necessary standard, rather than a higher bar, strikes the right balance of precision and cost-effectiveness.

Considerations for Determining Standards

To meet these specifications, manufacturers first need to test the optical glass against various reference models. Though each test tells manufacturers how to make tolerance adjustments, the tests can further increase the cost of production and the total amount of time it takes to fully produce the glass.

As a result, prioritize the following factors: 1) which specifications are the most important, 2) to what degree each specification needs to be met, and 3) how tight the tolerances for each specification should be. Consider the intended function of the optical glass and how it will be affected by certain specifications.

Optical Glass Parts at Swift Glass

Obtaining and understanding optical specifications can allow for significant cost and time savings for designers and suppliers alike. While none of these tests are required by any regulatory body, it’s critical to work with suppliers and manufacturers who uphold these standards in order to cut down on surface rejections and defects — and, therefore, reduce overall costs and lead times.

Swift Glass provides a wide range of testing services to ensure our products are of the highest possible quality and precision. Our team offers full-service precision optical glass component fabrication services for all types of high-volume projects.

Curious to know if your optical glass is flat enough? Try out our new Glass Flatness Conversion Table to see for yourself, and consider consulting with our experts for any other glass surface needs.

At Swift Glass, we specialize in creating high-quality glass components that balance tight tolerances with cost-effectiveness. Contact our team today to determine which specifications and tolerances are the best fit for your next order. You can also request a quote for pricing details.


Viscosity, Refractive Index and Other Important Glass Properties Involved in Material Selection

Glass is among the most versatile of materials. Depending on its composition, treatment, and manufacture, it can be customized for high performance in countless applications.

material-properties-chartIn order to get the right fit for your next glass project, remember to consult properties such as the corrosion resistance, thermal properties, viscosity, dielectric properties and refractive index of potential materials. These properties tell a lot about how a material reacts to its environment, which is especially important for your application’s performance.

Sample Material: Borosilicate

When compared to other types of glass, borosilicate has a high corrosion resistance to acid, but a low corrosion resistance to weathering. Its thermal expansion is very low, and its volume resistivity and thermal shock resistance are both high — but not the highest. Its light transmission is excellent.

Pyrex® and Borofloat® are common types of borosilicate, though both Schott and Corning craft a series of variations with increasingly specific properties.

What does all of that mean?

Because of its resistance to high temperatures and chemical corrosion, borosilicate makes an excellent material for the biomedical and research industries. It’s also an ideal material for optical, lighting and industrial applications.

Because this is a glass that demonstrates strength without being the absolute strongest, borosilicate is an affordable material, making it extremely popular in many industries. Of all possible glass materials, it’s the Swift Glass choice for all of our annular edge glass. Its edges can be ground specially to be sealed in a flange for biomedical, research, optical, optoelectronic, photonics and analytical applications.

Other Material Options

For the toughest situations, traditional glass materials may not be enough — no matter how naturally strong. Thermal tempering and chemical strengthening can further prepare glass for high-intensity applications, such as:

  • High Pressure Windows
  • Explosion-Proof Windows
  • Lighting Products
  • Industrial and Residential Doors

The additional safety and dependability offered by tempered glass serves many industries, from automotive to medicine.

Resources for Selecting Materials

For quick reference, the Swift Team has assembled a Glass Material Properties Chart addressing some of our most popular material choices, ranging all the way from soda lime glass to fused silica. We also offer material consulting from our team of experts, as well as tempering services for specialty projects.

Download the Glass Material Properties Chart now, or contact the team to learn more today.

Download Now: Glass Material Properties Chart

Glass Wafers: How Optics, Computers and Photonics Get the Right Glass

Computers, optical and other technological manufacturing industries require glass wafers as a carrier substrate for safe fabricating of delicate products like thin silicon wafers.

Glass Carrier WafersGlass wafers are also essential to the semiconductor, electronics, and biotech industries in a variety of applications.

Making Glass Wafers

Glass wafers are highly technical products that demand a highly technical production process, often requiring their own proprietary technologies. Here’s how Swift Glass utilizes its expert team and technology to craft these complex products:

  1. 1. Material Selection

Glass wafers begin with the highest quality glass. We typically work with Borofloat, Borosilicate, Quartz, and Eagle XG, selecting the most consistent glass sheet from the best batches. Wafers are cut from these sheets to be further processed.

  1. 2. Shaping

The carefully selected and cut material is then ground to build out the wafer’s general shape.

  1. 3. Edges and Details

The edge profile of the wafer is machined to specifications with the use of diamond tools. For example, a wafer could be crafted with a flat or notch, depending upon the design, and with an edge profile that is either flat-ground or pencil-ground. The notch, if designed, serves as a precise locator.

  1. 4. Lapping

The product is lapped, and the profile accuracy gets checked.

  1. 5. Polishing

Both sides of the wafer are polished.

  1. 6. Inspection

Glass wafer inspection must be highly controlled in order to guaranteeprecision — the product is taken to a clean room with climate control, and the profile is recorded by laser.

The laser passes over the glass three times while another gauge reads the wafer’s total thickness variation (TTV). The larger the wafer, the more critical the TTV.

Glass Wafers from Swift Glass

After more than eighty years of glass manufacturing, the Swift Glass Team has developed highly specialized design and production capabilities. We are proud to take on the complex challenges that come with specialty products like glass wafers.

For more information about our processes, check out our library full of free resources.

Check Out Our Chemically-Strengthened Glass at Optifab 2015

Swift Glass will be joining its glass manufacturing peers at the prestigious SPIE Optifab 2015 exhibition and conference next week in Rochester, New York.


The SPIE Optifab exhibition is the largest optical fabrication event in North America and acts as a forum to share and discuss the latest techniques and tools for the optical fabrication industry.

The event includes over 100 technical talks, covering glass manufacturing topics such as grinding and polishing, optical fabrication of freeform surfaces, metrology, optical materials, cleaning and coating, optical design, optical engineering, meter-class optics, and molded optics.

Swift Glass will be bringing our knowledge of glass fabrication to the forefront in our own exhibition. We will showcase a piece of chemically-straightened glass at Booth 504, and will have a team of highly skilled and experienced employees on hand to answer questions and provide information about the capabilities that we specialize in.

Optifab 2015 takes place from October 12-15 at the Joseph A. Floreano Rochester Riverside Convention Center, located at 123 E Main St. in Rochester, New York. Presentations will run from 8am until 6pm, daily.

Come join us in celebrating optical fabrication and learn about all the capabilities and materials Swift Glass works with. Contact us today to learn more about the event.

Photonics, Optics and the Tech of the Future

Swift Glass among the Region’s Optical and Photonics Specialists

Vice President Joe Biden recently visited Rochester, the “optics capital of the world,” to announce that our region has been chosen to host a new $600-million Integrated Photonics Center.

The creation of a national photonics institute means more than jobs and industrial growth; it’s the beginning of the next generation of American manufacturing.

optical-components-photonicsPhotonics research contributes to the function of countless daily tools: smartphones, high-speed Internet and wireless controllers, to start. It is closely related to optics: technology harnesses light for the development of smaller, faster and more energy-efficient devices.

Photonics touches a broad spectrum of industries: for example, manufacturing, global information technology, telecommunications, medicine, energy and national defense.

The idea is to transition devices from electron-based operations to using photons, or light. This includes the transfer of data from the internet, phones, TV, and radio with tools like lasers, fiber optics and optical detectors.

As a longstanding member of the optical community — and as a close neighbor to Rochester — Swift Glass is proud to have the specialized skills to bring new designs like these to life with working products and system components. Our glass materials alone carry unique traits applicable in modern technology, but our custom fabrication capabilities are where real innovation happens.

The skilled technical team at Swift specializes in every step of development, from prototyping to large-scale part production. Our state-of-the-art machining solutions and capabilities include:

  • Bending and Convexing
  • Chemical Strengthening
  • Beveling
  • Counterboring
  • Cutting and Drilling
  • Double Sided Lapping & Polishing
  • Flat Polish and Pencil Polish Edging
  • Milling
  • Pattern Cutting
  • Sagging
  • Seaming
  • Silk Screening
  • Surface Frosting
  • Tempering

We’re proud to have spent eighty years here in the Rochester area, sharing in the research, technology and thriving energy of the optical industry. As the oldest supplier of tempered glass in the United States, it’s inspiring to see these types of developments in the industry

Lighting, appliances and optics are part of the Swift Glass DNA, and we can’t wait to see what technology is to come. If you’re working on a custom project or prototype of your own, reach out to the team today — they’d be happy to help.


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