CIE Whiteness (ISO 11475):
| What | The whiteness of the substrate, expressed in a percentage, is derived from the CIELab values and in fact is a diffuse reflection of light on all waves of the visible light range. |
| Why | Higher whiteness gives higher contrast. |
| How | Whiteness according to CIE is determined with an Elrepho, using a D/65 light source, UV included, and a viewing angle of 10°. |
| Calculation | Report the average of 10 significant values and the standard deviation of both front and back. |
| Note | Other light sources are D50/2° incl. UV and C/2° excl. UV according to ISO 11476. |
Andere lichtbronnen zijn D50/2° incl. UV en C/2° excl. UV (ISO 11476)
CIE Brightness (ISO 2470):
| What | The percentage of white as a direct reflection, measured in the blue range of the visible spectrum. |
| Why | Brightness has impact on readability and colour intensity. |
| How | Determined with an Elrepho, using a D65/10° or D50/2° light source and a R457 filter. Since the wavelength of 457 nm is exclusively blue, the measured value reflects a whiteness excluding all wavelengths in the red and green range. D/50 measurement is especially suited for those substrates to which no extra OBA’s (Optical Brightening Agents) and/or colouring agents have been added. D/65 is used for those substrates with a certain amount of fluorescence, that promotes whiteness. |
| Calculation | Report the average of 10 significant values and the standard deviation of both front and back. |
Shade CIELab en Delta E (ISO 5631-2):
| What | Reflection of colour is referred to as a combination of tint, saturation and dark/light value. The CIELab method measures shade, where L* = the lightness (100% is perfect white, 0% is perfect black) a* = colour on the red – green axis (-a = green, +a = red) b* = colour on the blue – yellow axis (-b = blue, +b = yellow)Delta E76 (∆Eab) is a value for fluctuations in the shade between more sheets of the same production run. A shade is consistent if the shade differences are not visible, i.e. ∆Eab is lower than 1. |
| Why | CIELab and ∆E values are important for reproducing the same printed matter more than once (e.g. corporate image) and nowadays especially for standardisation according to ISO 12647-2. |
| How | CIELab values are determined with an Elrepho, using a D/65 light source, UV included, and a viewing angle of 10°. |
| Calculation | Report the average of 10 significant values of both front and back. |
| Note | 1: spectrophoto meters in agreement with ISO 13655 as used in the graphical industry have no scattering device for diffuse reflection of light; it shines the light directly onto the substrate’s surface under 0:45 or 45:0 degrees. 2: ∆Eab < 1: hardly noticeable 3: The light sources C and D50 are described in resp. parts 1 and 3 of this ISO standard. These differ in light source and viewing angle, however they do not differ in other aspects of the method described above. |
Shade CIELab en Delta E (ISO 13655):
| What | Reflection of colour is referred to as a combination of tint, saturation and dark/light value. The CIELab method measures shade, where L* = the lightness (100% is perfect white, 0% is perfect black) a* = colour on the red – green axis (-a = green, +a = red) b* = colour on the blue – yellow axis (-b = blue, +b = yellow)Delta E76 (∆Eab) is a value for fluctuations in the shade between more sheets of the same production run. A shade is consistent if the shade differences are not visible, i.e. ∆Eab is lower than 1. |
| Why | CIELab and ∆E values are important for reproducing the same printed matter more than once (e.g. corporate image) and nowadays especially for standardisation according to ISO 12647-2. |
| How | CIELab values are determined with a Techkon Spectrodens Advanced, using M0, M1 or M2, viewing angle 2° |
| Calculation | Report the average of 10 significant values of both front and back. |
| Note | ∆Eab < 1: hardly noticeable ∆Eab between values 1 and 2: visible to the trained eye ∆Eab between values 2 and 4: visible to the eye ∆Eab value > 4: complaint worthy ∆Eab value > 6: different colour |
Opacity (ISO 2471, TAPPI T 519):
| What | Degree of opacity, expressed in a percentage. Paper that lets through a lot of light is transparent, paper that lets through hardly any light is opaque. The higher the value, the opaquer. |
| Why | Of importance when printing two-sided. A difference of 1% is visible to the naked eye in case of opaque papers. |
| How | Determined with an Elrepho, using a C/2° light source. It is in fact the ratio of reflection of a stack of the paper (considered to be 100% opaque) and one sheet of this paper, measured over a black cavity. |
| Calculation |  Where: R∞ is the reflection value of a stack of the paper (considered to be 100% opaque) R0 is the single sheet value measured over a black cavityReport the average of 10 significant values and the standard deviation. |
Transparency/Transmittance of light (ISO 22891):
| What | Ratio between light reflected by a sheet of paper and light reflected by that same sheet over a black cavity, expressed in a percentage. |
| Why | In cases you should be able to see through paper, e.g. tracing paper, specific wrappings, or paper for certain (creative) applications. |
| How | Determined with an Elrepho, using a C/2° light source. The reflection is measured over a white working standard of known values. Subsequently this measurement is repeated over a black cavity. |
| Calculation | Transparency is calculated conforming the Kubelka-Munk analysis. Report the average of 10 significant values and the standard deviation. |
Delta UV (ISO 2470):
| What | An indication of the amount of present Optical Brightening Agents (OBA’s) in the substrate, expressed as a percentage. |
| Why | Some applications should have none or as least as possible optical brighteners added, like paint or ink colour samples or machine readable transaction forms (giro credit slips) |
| How | Determined with an Elrepho. Brightness is measured using a D65/10° light source and a second time on wavelength 420 nm (total UV blockage). The Delta UV is the difference between both values. |
| Calculation | If, in the case of fluorescent samples, measurements are made with a filter with a cut-off wavelength of 420 nm placed in the light beam, it is possible to determine the ISO brightness of the non-fluorescent substrate and thus to calculate the contribution of the fluorescent whitening agent to the ISO brightness:
Report the average of 10 significant values and the standard deviation. |
| Note | OBA not added is not the same as OBA free. Not added means that there may be some leftover OBA from a previous making on the paper machine that did have OBA. OBA free means the substrate is produced on either a dedicated OBA free paper machine or an additive is used make the paper optically dead. |
Gloss converging beam 45°/75° (ISO 8254, TAPPI T480):
| What | Paper gloss is the reflection of light on the paper surface in a certain angle, expressed in GU (Gloss Units). Printing gloss is measured after 24 hrs drying of the ink, using a 75° angle. Delta (∆) gloss is the difference between the both. |
| Why | Depending on the application. For a printing form with hardly any text and many photographs, often a gloss finish of the paper surface is chosen. For a combination of text and photographs one often chooses a half matt or matt finish. Photographs are then enhanced by applying varnish or lacquer. In each case a printer will be most interested in Delta gloss, a paper manufacturer in paper gloss (though the latter may vary in adding certain chemicals to create a good Printing – and therefor a good Delta gloss. |
| How | Gloss is measured with a gloss meter on front and back in both MD and CD. In case of printing gloss only the printed side(s.) |
| Calculation |  Where: GUU = gloss unprinted GUP = gloss printedReport the average of MD/CD of 10 significant values and the standard deviation. |
| Note | Usually an angle of 75° is used for coated and SC paper and 45° for other uncoated paper. |
Gloss converging beam 20°/60°/85° (ISO 8254, TAPPI T653):
| What | Paper gloss is the reflection of light on the paper surface in a certain angle, expressed in GU (Gloss Units). |
| Why | Depending on the application. For a printing form with hardly any text and many photographs, often a gloss finish of the paper surface is chosen. For a combination of text and photographs one often chooses a half matt or matt finish. Photographs are then enhanced by applying varnish or lacquer. |
| How | Gloss is measured with a gloss meter on front and back in both MD and CD. |
| Calculation | Report the average of MD/CD of 10 significant values and the standard deviation. |
| Note | Measurement at 20° is especially designed for high gloss surfaces, such as cast coated substrates. |
