Custom Witness Sample Fabrication

Best practices suggest that when coating or setting up an optical component, it’s best to use a witness sample (also called a “test piece”) to ensure that the actual part will match your specific coating specifications and your application.

Sydor Optics also offers witness samples for the measurement of coating stresses on substrates. The size and thickness of a witness sample will typically match your finished product.

Available Materials

Based upon customer demand, Sydor Optics offers optical witness samples made from the following substrate materials. Of course, if you don’t see a material you need, please contact a Sales Engineer who will gladly discuss additional options that may be available.

Fused Quartz
Witness Samples

Fused Silica
Witness Samples

BOROFLOAT® (Borosilicate)
Witness Samples

B 270®
Witness Samples

N-BK7® (S-BSL7)
Witness Samples

Silicon (Si)
Witness Samples

Witness Samples

Witness Samples

Coating Witness Sample Manufacturing Limits

Manufacturing limits depend upon the part size and substrate material and should be used as a general reference. Please contact a Sales Engineer, who will gladly discuss our capabilities based on your specifications.



Diameter customer specified (typically 25mm – 50mm)
Thickness customer specified (typically 1mm)
Thickness Tolerance ± 0.1mm
Cosmetics (MIL-PRF-13830B) 60-40 to 20-10
Surface Roughness ≥ 5 Ǻ rms
Reflected Wavefront Error (RWE) – before coating ≥ 1/10 wave over clear aperture
Transmitted Wavefront Error (TWE)* – before coating ≥ 1/10 wave over clear aperture
Clear Aperture ≤ 95%
*Interferometric Scale Factor (ISF) of 0.5 – Single-Pass