Interested in a little light reading?

Contrast Ratio Opacity measurement quantifies how opaque a sheet sample using two readings. One reading is taken with the black glass or light trap backing the sample at the port. The second reading is taken with the sample backed by a white tile or the white sample clamp insert. EasyMatch QC will prompt you for the proper backing when taking opacity measurements.

Opacity Measurement in EasyMatch QC

To perform opacity measurements in EasyMatch QC, first standardize the instrument in a reflectance mode. Once standardized in reflectance, select “Opacity” to display in the Color Data View by going to Options/Read Method’.

A new window will open that allows you to choose Contrast Ratio Opacity as a read mode. Additional display options include the option to display:

• Y Brightness value of the sample backed with the white backing which can be used to indicate the overall reflectance or luminous brightness as additional optical information.
• Y Brightness value of the sample backed by black backing which is the second component of the Contrast Ratio Opacity calculation.

A typical display is just Opacity with some users selecting the Opacity, Yw combination.

Another option is the choice of an illuminant and observer for opacity reporting. Chose C/2 if you have no prior conditions. Once all of your selections are made click ‘OK’ to save and these metrics will be displayed in your Color Data View.

Put your mouse over the Color Data View/Right Click/Configure to select additional metrics such as CIE L*, a*, b* D65/10 color values as a complete quantifier of the color, or Yellowness Index E313 C/2 or D65/10 as a single quantifier for yellowness of white materials. Different metrics provide different optical information. Color values quantify the color of the sheet; contrast ratio opacity quantifies how opaque the sheet material is.

Both “hydro” coming from Greek origins for water and “hygro” coming from the Greek “hygrós” for wet or moist, tend to be used in two terms for the same optical phenomena.

ASTM E284 on standard appearance terminology prefers the name “hygrochromic”.

When used with industrial and commercial products, there is more than one definition of “opacity” as an optical property.

Contrast Ratio Opacity (OP) measurements quantify how close to opaque a near-opaque material is.

The measurement is a two-part program metric where the CIE Y (luminance or brightness) value is first measured the sample backed by a black background, followed by a second measurement of the Y value of the sample backed by a white background. The resulting fraction is expressed as Y%, calculated as follows:.

As Y Brightness is a colorimetric value calculated based on a CIE illuminant/’observer

condition, this must be specified and reported. The illuminant/observer choice will vary depending on the industry – A/2 (automotive), C/2 (historical and default choice), D65/2 (printing) and D65/10 (often used in current color measurements). As Opacity is a ratio, the results will be nearly identical for any of these illuminant/observer conditions.

Typical applications where contrast opacity is an important appearance characteristic are coating drawdowns and single sheets or layers of paper, plastic and textiles.
The primary appearance concern is lot-to-lot consistency in a material that is inherently not quite opaque.