How to Measure Reflective Surfaces

Measuring reflective surfaces poses a challenge because the effect of gloss can actually change the color appearance of a sample. The surface reflection of light is what causes the gloss effect. So how can you accurately measure reflective or shiny surfaces?

Use a sphere instrument: A sphere spectrophotometer is specifically designed to reliably measure color on samples with shiny or reflective surfaces. It diffusely illuminates the sample and measures at 8° from perpendicular. The images below compare operation of a 45/0 spectrophotometer (on the left) with a sphere spectrophotometer.

Sphere spectrophotometers can provide reflectance measurements in two ways: specular included (SPIN) and specular excluded (SPEX). To include gloss in the measurement, the specular port closes. To exclude gloss, the specular port opens to let the specular component escape so it’s not included in the measurement. So you have the flexibility of including or excluding gloss depending on the type of sample and your objectives.

As the image above demonstrates, if you measure the same glossy sample with a 45°/0° instrument and a sphere instrument reading specular excluded, the data won’t be the same. That’s because the 45°/0° spectrophotometer excludes all of the gloss, while when the specular port in a sphere is closed it doesn’t allow any of the gloss effect to escape.

When should you use SPIN or SPEX?

When do you measure SPIN? When do you measure SPEX? Here are some guidelines.

• Check with your customer. Some will require a SPIN tolerance, while others will require a SPEX.

• If you’re interested in the appearance of a sample, you should measure SPEX. However, if you want to detect pigmentation or compare textures of the same material, you should choose SPIN.

• The texture and/or gloss of your samples can vary greatly, especially with textiles. To truly evaluate the color without respect to gloss or texture, you need a SPIN reading.

• If you’re measuring pieces with various textures, such as plastic moldings, and want to compare the surfaces for color variation, you should measure SPIN.

Which instrument is right for you?

We’re happy to help you choose the right color measurement and management solutions for your needs. Speak to one of our color experts today. And be sure to check out our promotions, good through the end of the year, to save when you invest in an X-Rite sphere solution.