Brightness

D65 - Brightness (%) ISO 2470
ISO - Brightness (%) ISO 2471-1

Pulp is never entirely white but has a natural yellow colour because of the wood itself. Because of that the brightness is measured.
D65 Brightness is measured by illuminating a paper sample with an instrument that emits D65 light, i.e. a light that is related to daylight with the same amount UV light as in a winter day. The reflected light is filtered through a glass filter that only allows blue light to leave. The brightness is measured by indicating the amount of incident blue light that is reflected from the paper. With bleaching the yellowness is reduced and blue will be more expressed. The wavelength of the blue light is 457 nm.

A related term to D65 Brightness is ISO Brightness. In this method the paper sample is illuminated with the light of a bulb, instead of D65 light. The method is used if the paper sample not contains any fluorescent compounds.

Whiteness

CIE Whiteness % former SCAN-P 66:93

The impression of whiteness consists of the perceived lightness and the hue, i.e. how much the hue deviates from neutral. The CIE Whiteness of the perfect white is 100.
CIE Whiteness Fluorescence % former SCAN-P 66:93

The CIE Whiteness Fluorescence measures to what degree the whiteness of the paper is affected of the fluorescent compounds. With fluorescence it's possible to get a whiteness above 100 %, as invisible light is transferred to visible. (See Brightness Fluorescence above)

Luminance

Y value D65/10° - Luminance (%) ISO 2471
Y value C/2 - Luminance (%) ISO 2471

The Y value is an indicator of the perceived lightness, measured with an instrument whose response to the wavelengths of light corresponds to the response of a healthy eye, i.e. the full spectrum of visible light, which means all colours from blue to red and in between of the "rainbow".
The Y value is measured with an instrument that emits D65 light, i.e. a light that is related to daylight with the same amount UV light as in a winter day. The reflected light are measured in a different wavelength compared with Brightness. The sample is illuminated vertical to its surface and the detector is located 10° from the vertical axis.

Y values are percentages. The Y value of a black non-reflecting material is 0% and the value of the perfect diffuser is 100%. Y value is also named as luminance, especially in the past.

Luminance measurement on newsprint and improved newsprint is done by using indoor illumination, C/2.

Opacity

Opacity C/2° (%) ISO 2471

Opacity is a measure of a material's ability to obstruct the passage of light. Sufficient opacity is important to prevent printed text from showing through in a harmful manner on the reverse side of a paper. The opacity of a completely opaque paper is 100%.
Opacity is measured with an instrument that emits C light, i.e. a light that is related to daylight but without UV content. The sample is illuminated vertical to its surface and the detector is located 2° from the vertical axis, as shown in the figure below. Opacity is the ratio between the Y value of paper measured under conditions C/2° and the Y value of a single sheet measured under the same conditions against a black backing.

L*, a*, b*

L* D65/10° (%) SCAN P72
L* C/2 (%) ISO 5361

L* is a measure of perceived lightness. The scale of L* is 0–100.
L* is measured with an instrument that emits D65 light, i.e. a light that is related to daylight with the same amount UV light as in a winter day. 10° is the viewing angle.

If the Y value is over 60 %, the L* is fully possible to be exchanged with the Y value, because they correlate near to 100 %.

a* D65/10°
a* C/2
a* is a measure of the hue on the red/green axis. A positive value of a* means red and a negative value means green.

a* is measured with an instrument that emits D65 light, i.e. a light that is related to daylight with the same amount UV light as in a winter day. 10° is the viewing angle.

b* D65/10°
b* C/2
b* is equivalent with measure of hue on the yellow/blue axis. A positive b* means a yellow hue and a negative value means a blue hue.

b* is measured with an instrument that emits D65 light, i.e. a light that is related to daylight with the same amount UV light as in a winter day. 10° is the viewing angle.

Gloss

Gloss Tappi 75°, ISO 8254-1

Gloss is the attribute of a surface that makes the object look shiny or lustrous. It depends on specular reflection from the surfaces. High gloss is a desirable property in a high quality, prestigious image.

The tone range of a glossy image is wider than that of a matt surface. Deeper blacks and more saturated colours are possible when printing on a high gloss surface.

At Ortviken Gloss is measured with an angle of 75°.

Porosity/Air permeance

Bendtsen Porosity (ml/min) ISO 5636-3

In a paper sheet the fibres and filler particles are agglomerated together to a strong and dense packing, but between the fibres and fillers is still some included air, with the process of calendering the porosity is significantly reduced by compressing the sheet and by collapsing the fibres.
The measurement of porosity describes the potential air flow trough a sheet in z-direction, the porosity is measuring the air flow which is able to pass this porous structure of the sheet. The measurement is done with a defined air pressure (1,47 kPa) to the surface of the sheet and with a defined measurement area (10 cm²).

Roughness

PPS-Roughness (µ) ISO 8791-4, 1,0 Mpa

A paper surface topography is characterised by the fibres and fillers and the intermediate pores, such a surface is never so even or smooth like a glass plate; to characterise this topography in a simple way we measure the pps-roughness by measuring the air flow on the surface of a paper sheet, similar to a porosity measurement, not in z-direction but in x- and y direction.
The measurement is done with a defined measuring device, with defined pressure of the measuring facility to the paper surface and with a defined rubber plate on the contrary paper side, the resulting values are calculated from pressure differences and describe the width of the slit which enables the air to pass between the measuring facility and the paper surface in x-y direction.

Thickness and Bulk

Thickness (mm) ISO 534

A paper's thickness is measured in micrometres' (µm) – thousandths of a millimetre – and is the distance between the paper's two surfaces. Thickness is in many ways an important consideration in paper selection, as it affects the stability, feel and of course thickness of the final printed product.

Bulk (cm³/g)

Bulk is the inverse of density, i.e. the number obtained by dividing the thickness of paper expressed in microns (1 µm = 0.001 mm) by its grammage expressed in g/m2. Paper is said to bulk well when the thickness seems high for its grammage and to bulk low when the reverse is the case. A high bulk stands for a less compact sheet.

Tensile and Tear strength

Tensile (N) ISO 1924-2

Is the measurement of a force (N) to elongate a defined paper stripe to its break. The width of the test stripe is 15 mm. Tensile is measured in md and cd, the values in MD are significantly higher than the values in CD, the reason for this is the orientation of the fibres during the forming process in the paper machine in MD.

Elongation (%) Stretch at break ISO 1924-3

This elongation of the paper test stripe in the tensile measurement to the break is called strain, the higher the strain the higher is theoretically the flexibility of the paper in the printing machine to resist against tension-variations.

Tear or tear resistance (mN) ISO 1974

The tear strength is the force a singel sheet can resist when one part of the paper is taken out of the plane, i.e. in the z-direction and perpendicular to both MD and CD. Tear strength is measured according to the Elmendorf method.