SCHOTT B 270® Coating witness samples
The role of coating witness samples
What are coating witness samples?
Coating witness samples—also referred to as “witness glass” or “test pieces” by coating professionals—are precisely manufactured glass substrates used to simulate coating results on themselves, rather than on actual production components. They serve as reliable test surfaces for evaluating, calibrating, and validating coating performance. Additionally, witness samples are often retained as records of a specific coating run or used as reference standards to demonstrate or measure coating quality over time.“A coating witness sample is a trial unit used to test coatings—so you can check, calibrate, and confirm the coating quality before applying it to your production units.”
Why use witness samples?
Witness samples offer a practical and risk-free way to validate coating processes before applying them to valuable or sensitive components.- Quality assurance: Confirm parameters before entering production with actual components.
- Process monitoring: Run intermediate checks to monitor layer thickness, uniformity, transmission etc.
- Testing and calibration: Fine-tune parameters for setting up your coating equipment—whether during initial configuration or after service and maintenance.
SCHOTT B 270® – The optical standard
Why choose B 270® for witness samples application?
SCHOTT B 270® is a high-purity, super-white crown glass developed specifically for demanding optical applications. B 270® is the ideal substrate for coating witness samples due to its exceptional purity and optical clarity. Its fire-polished surface free form tin-contamination makes it an optimal substrate for coating witness samples, while its broad spectral transmission (390–2170 nm) allows comprehensive performance evaluation across UV, VIS, and NIR bands. These properties make B 270® a reliable, repeatable standard for validating coating quality across diverse coating methods.
Compatibility with a wide range of coatings
SCHOTT B 270® enables a stable, high-purity witness sample for virtually all modern optical coatings. Its outstanding transmission properties and material homogeneity make it an ideal substrate for both functional and decorative coatings across the UV, visible, and NIR spectrum.
Whether you're applying precision filters, reflective layers or protective coatings, B 270® ensures consistent optical performance enabling reliable, repeatable coating processes across batches and applications.
B 270® Witness samples are suitable for a wide range of coatings including:
- UV, visible, and NIR filters (including short-pass, long-pass, bandpass, notch, beam splitters)
- Mirrors (such as aluminum, silver, dielectric)
- Anti-Reflective (AR) and High Reflective (HR) coatings
- Conductive coatings (ITO, AZO, FTO, etc.)
- Protective layers (hard coatings, hydrophobic, oleophobic)
Beyond coating types, B 270® also meets the specific demands of various deposition techniques - each of which places unique requirements on the substrate.
Compatibility with diverse coating methods
Coating witness samples must meet the specific demands of various deposition techniques, and SCHOTT B 270® offers a reliable, single-material solution that performs consistently across all major methods. Combined with its affordability and wide availability, B 270® is an ideal choice for repeatable, single use testing during iterative process optimization.
Benchmark your coating test parameters with SCHOTT B 270®
To evaluate coating performance and ensure it meets application-specific requirements, several key test parameters are used—each supported by the reliable properties of SCHOTT B 270®.
- Optical performance: B 270® offers high transmission (up to 92% at 2 mm) and a broad, stable spectral range from 390–2170 nm. Its consistent refractive index (1.52) and homogeneity ensure that any spectral variations observed during testing are due to the coating—not the substrate—making it ideal for UV, VIS, and NIR applications.
- Coating thickness & uniformity: Its smooth, uniform surface supports precise measurements using ellipsometry or profilometry. Any non-uniformity detected can be confidently attributed to the coating process.
- Adhesion: The fire-polished surface (≤ 1 nm roughness) is free from contaminants like tin, promoting strong film adhesion. A passed adhesion test on B 270® reliably reflects coating robustness.
- Abrasion resistance: B 270®’s clean, defect-free surface ensures that wear observed during testing is due to the coating itself. Its affordability makes it ideal for single-use abrasion tests in high-throughput environments.
- Environmental and UV exposure: With non-solarizing behavior, B 270® withstands temperature cycling, UV exposure, and laser irradiation—making it suitable for coatings used in harsh or long-term environments.
- Chemical resistance: B 270® resists acids, alkalis, and common cleaning agents. If a coated sample remains pristine after aggressive cleaning, it confirms both coating and substrate durability under real-world conditions.
With its proven performance across all key test parameters, SCHOTT B 270® stands as the trusted standard for coating witness samples—delivering the consistency, clarity, and reliability needed to validate coatings with confidence.
Technical details
SCHOTT B 270® glass offers excellent luminous transmission (up to 92% at 2 mm thickness), making it an ideal material for cover glass in night vision systems. Its excellent transmission with a broad and stable spectral range from 390–1800 nm without dips ensure that light passes through with minimal loss, enabling bright, high-contrast imaging.
Reliable colorimetry values provided by SCHOTT for B 270® support precise coating calibration and validation. Thanks to B 270®’s inherent material consistency, coating professionals can rely on its colorimetry data to fine-tune color, transmission, and reflectance with confidence. These values enable accurate coating design, help maintain both visual and optical performance standards and ensure coatings consistently meet customer requirements over time.
| Colorimetry | Values | ||
|---|---|---|---|
| Chromaticity coordinates ** at d = 2.0 mm | D65 | x | 0.313 |
| y | 0.329 | ||
| A | x | 0.448 | |
| y | 0.408 | ||
| General color rendering index Ra at d = 2.0 mm | 100 | ||
** Chromaticity coordinates (color locus) are referred to the named Standard Illuminant according to CIE (2°-Observer)
| Property | B 270® Advantage |
|---|---|
| Homogeneity | Highly consistent material properties across batches ensures reliable, repeatable coating assessment |
| Optical Transmission | 92% with 2 mm; Stable max. transmission of > 90% in a broad spectrum of 390–2170 nm without any noticeable dip |
| Surface Finish | Fire-polished ≤ 1 nm roughness; minimal touch polishing for optical flats |
| Mechanical Processing | Softer glass, enabling fast edge processing, or polishing making it an easy-to-process substrate for making coating witness samples |
| Colorimetry Data | Provided as standard—supports precise color, reflectance, and transmission control |
| Factor | Optical Glass | Float Soda-Lime | B 270® |
|---|---|---|---|
| Material Homogeneity | High | Low | High |
| Thickness Availability | Low | Limited | Extensive |
| Surface Preparation Effort | High | Moderate | Minimal, if needed |
| Color Consistency | Consistent | Not always | Very consistent |
| Price-Performance | ++ | +++ | +++++ |
B 270® is available in a wide range of thicknesses*:
| Thicknesses | ||
|---|---|---|
| 0.80 mm | 2.00 mm | 2.80 mm |
| 0.90 mm | 2.10 mm | 3.00 mm |
| 1.00 mm | 2.15 mm | 3.15 mm |
| 1.10 mm | 2.20 mm | 3.30 mm |
| 1.15 mm | 2.25 mm | 3.50 mm |
| 1.20 mm | 2.30 mm | 4.00 mm |
| 1.35 mm | 2.40 mm | 4.50 mm |
| 1.50 mm | 2.50 mm | 5.00 mm |
| 1.65 mm | 2.65 mm | 5.50 mm |
| 1.70 mm | 2.70 mm | 6.00 mm |
| 1.85 mm | 2.75 mm | |
*Other thicknesses on request.
