What is the meaning of Lightfastness for masterbatch ??


Lightfastness is a property of a colourant such as dye or pigment that describes how resistant to fading it is when exposed to light.[1][2][3] Dyes and pigments are used for example for dyeing of fabrics, plastics or other materials and manufacturing paints or printing inks.

The bleaching of the color is caused by the impact of ultraviolet radiation in the chemical structure of the molecules giving the color of the subject. The part of a molecule responsible for its color is called the chromophore.[4][5]

Light encountering a painted surface can either alter or break the chemical bonds of the pigment, causing the colors to bleach or change in a process known as photodegradation.[6] Materials that resist this effect are said to be lightfast. The electromagnetic spectrum of the sun contains wavelengths from gamma waves to radio waves. The high energy of ultraviolet radiation in particular accelerates the fading of the dye.[7]

The photon energy of UVA-radiation which is not absorbed by atmospheric ozone exceeds the dissociation energy of the carbon-carbon single bond, resulting in the cleavage of the bond and fading of the color.[7] Inorganic colourants are considered to be more lightfast than organic colourants.[8] Black colourants are usually considered the most lightfast.[9]

Lightfastness is measured by exposing a sample to a lightsource for a predefined period of time and then comparing it to an unexposed sample.[2][3][10]

source  :You are not allowed to view links. Register or Login

The lightfastness or permanence of a pigment is its resistance to change on exposure to light. This depends on the chemical nature of the pigment, its concentration, and the medium in which it is employed — oil, watercolour, acrylic.

Permanence is especially important in painting because the length of time a pigment retains its original colour value determines the life expectancy of the work of art.

The pigment must be lightfast. Pigments must also be chemically and physically stable and must not break down or change in any way as they age So you can see that it is important to know your pigments!

As an aid to artists, our comprehensive Oil and Acrylic Colour Charts list not only the colour name, but also individual pigment lightfastness rating, transparency and opacity details for every colour.

There is now a worldwide standard for permanence. The independent ASTM (American Society for Testing and Materials standard) was established and ratings from this organisation represent the most standardized classification in use for artists' materials. ASTM classification monitors quality, permanence and health guidelines. These pigment ratings were established in 1984.

To help you identify paints that are lightfast, look for the official ASTM rating information on individual paint tube labels. You will also find full ASTM information on each brands Colour Chart.

The lightfastness ratings are:
ASTM I — Excellent Lightfastness
ASTM II — Very Good Lightfastness
ASTM III — Not Sufficiently Lightfast to be used in artists' paints

NOTE: The ASTM ratings were done many years ago by Henry Levison (the inventor of Liquitex) during his retirement and very little updating has been done since. As a consequence we have some colours without ASTM ratings, but which do have BS ratings. We therefore also give the B/S (British Standard) woolscale ratings, which have been used to evaluate a larger number of pigments, and which give more specific information noting pigments at full strength, mid tint (with white added) and pale tint, (more white added).

The BS rating for pigment lightfastness goes from 8 which is absolutely lightfast to lower numbers which are progressively less so.

It also shows that any colour in mass tone is more lightfast than when tinted with white: 1/3 ISD (International Standard Depth) is about ½ to 1/3 strength and the lowest is 1/25 ISD which is a very pale tint.

The information is more accurate than the ASTM ratings, because the pale tints at 1/25 ISD level were never tested by ASTM and it is in the palest tints that unreliable colours fade most.

Our stringent controls mean you can have total confidence in the permanence of every pigment used in all of our professional artist' paints.

For more information on ASTM ratings please visit You are not allowed to view links. Register or Login

source : You are not allowed to view links. Register or Login

Lightfastness

The applied colour is then checked for lightfastness using a special "yardstick". The yardstick is known as a "blue wool scale" and consists of eight strips of wool fabric, each dyed using a different dye with different lightfastness properties. The samples are placed in a special light-test device, where they are subjected to the light of a xenon lamp (very similar to sunlight). Part of the test strips and the samples are exposed to the light, and part of them is covered to beused as a reference later. This standardised test is run until the most lightfast test strip – Level 8 – has begun to fade slightly. The colour samples are then compared to the test strips and given a lightfastness rating. The rating consists of the level of the blue scale whose change in colour most closely corresponds to the change in the colour samples.
A Measure of the Durability of Artists´Colours

Any artist who is concerned about the longevity of her works will put a premium on the lightfastness of her paints. Light has a dramatic impact on works of art: both in a positive sense, in terms of the effect of colour, and in a negative sense, in terms of their durability – unless highly lightfast artists' colours are used.

Everyone has seen the negative effects of light on low-light-fast colours, especially in bright fabric or printed material. As these products are not designed to last for a long time, the intensity of their colours degrades significantly in a short time. Direct sunlight is the biggest culprit in causing colours to fade. Light also degrades materials – wood and plastics become brittle, while newspaper turns yellow.

Works of art, on the other hand, are supposed to be long-lived, with colours whose brilliance and luminosity remain unimpaired after years or even decades. We at Schmincke have always stressed the importance of quality, including the lightfastness of our artists' colours.

While all the components in an artists' colour – pigments, binders and special additives – determine how lightfast the dry layer of paint will be, lightfastness depends mainly on the kind of pigment in the colour. The durability of a particular hue is not an accidental property. There are many ways to produce the pigment and many different components that can be used in the artists' colour (formula). Which of these options are selected greatly determines the final result of the production process. The ability to develop the "right" formula that also meets all the key requirements for an artists' colour is an essential piece of "know-how" in the production of artists' colours. It is, in essence, the secret behind high-quality artists' colours and maximum lightfastness.

At Schmincke, we place the utmost importance on speci-fically optimizing formulas to maximise lightfastness and on maintaining our current quality standards. That requires using an objective testing procedure. One such procedure, a "lightfastness test", is as follows: The lightfastness tests are always run on the finished Schmincke colours, not on individual components of the formula. This is important for the simple fact that even those paints with extremely lightfast pigments may change colour if the wrong binders or additives were used. Thus, we don't merely check how the pigment changes (colour fading), but can instead see the entire gamut of changes to the colour (darkening, changes in lustre, etc.).

Here's an example: In and of itself, the pigment titanium white is extremely lightfast. Once mixed in an oil colour based on pure linseed oil, however, it will eventually darken from its initial titanium white. This earns it a poorer lightfast-ness rating, and is one of the reasons why we at Schmincke do not use linseed oil as the main binder in light or white colours.

Schmincke designs its tests to reflect the environment in which the colours will be used. For example, each colour type is applied to a standard ground using typical applica-tion techniques for that particular colour (for HORADAM® watercolours, this would consist of defined scumbles on artists' water-colour paper).



Resistance to sunlight is also tested in real-life sunlight conditions: on Schmincke's rooftop, where colours are tested in a rack at a 45° slope facing south. Unlike the ,,quick" xenon test, this test can last from 2 to 2,5 years, depending on the actual amount of solar radiation.

We carry out this extensive procedure every time we change the formula – and not just every time we change the pig-ment – in order to check that our colours still meet our stringent lightfastness standards. Our many years of experience have shown that consistently rating and documenting the lightfastness of our products in brochures and on tube and bottle labels gives users extremely specific, understandable and practical information about the lightfast-ness of the overall system.

source : You are not allowed to view links. Register or Login

You are not allowed to view links. Register or Login

Lightfastness

Light fastness should be defined in terms of the entire paint, not only for the pigments itself. Binders impart an additional degree of protection for the pigment. Other components such as the presence of water or chemicals, for example, in the atmosphere or in the color system itself will also affect the lightfastness.

Mixtures with other pigments can also affect the light-fastness:

    Titanium dioxide, for example, promotes the loss of light in real-organic pigments. Therefore, high mixing ratios of titanium dioxide can result in poorer light fastness.
    Iron in turn can improve the light fastness of organic pigments, due to the fact that it is an effective absorber of UV light.

In order to compare the light fastness of pigments internationally the "Blue Wool / ASTM Light Fastness Standard" has been established. The "Blue Wool Scale" has its origin in the textile industry. ASTM D-4303 is the "standard of the American Society for Testing and Materials".

The following table gives an overview of the eight blue woolscale units 0 (extremely poor light fastness) to 8 (extremely light-fast), and the approximate correspondence between the blue wool scale standard and the five ASTM lightfastness categories.

The units of the "Blue Wool Scale" as well, and the ASTM are used for marking the lightfastness of oil paints.
The following table is a guide for the selection of artists' colors in terms of their light fastness.


Lilly Artist Oils are characterized by the means of the ASTM standard.
Two exceptions (PR83.1 and PY3) are in our range off colors with lightfastness II (7-8).
Both pigments were included due to their history and common usage.

source : You are not allowed to view links. Register or Login

 DIN ISO 12040
Graphic technology - Prints and printing inks - Assessment of light fastness using filtered xenon arc light (ISO 12040:1997)