The Importance of being Permanent

Winsor & Newton Advert from c. 1947-1948

Making sure your paintings stand the test of time

It’s funny to think that the materials we make and use will last so much longer than we will ourselves. Even pigments which we class as moderately durable like Alizarin Crimson will last hundreds of years untinted in oil colour.

And why does it really matter?  Every painting takes time, care and effort to complete, it can be heartbreaking to see all of your creative effort undone as a painting either fades or even worse starts to fall apart. Furthermore if you exhibit or sell your work you will want to be sure that your painting remains as true in colour and strength as the day you completed it.   The good news is that today’s artist is extraordinarily lucky to have more choice and permanence than ever before, with almost every hue in varying degrees of strength and opacity.   It is therefore well worth using and investing in good quality art materials to ensure that your work will remain the way you intended it to be for many years to come.

In this article we are going to look at how pigments are classed as permanent as well as the other elements which affect the permanence and durability of each painting category.

Pigments

The permanence of pigments is really their lightfastness ie;  their resistance to change when exposed to light, especially ultraviolet light. The permanence of each pigment is assessed by the pigment manufacturer using the Blue Wool Scale, a series of 8 swatches of blue wool, 1 being the deepest and 8 being the weakest.

Blue wool scale swatch - picture courtesy of SDC Enterprises - www.sdcenterprises.co.uk

Pigments like the Earths and metal oxides like Cobalts are 8. Synthetic organics like phthalocyanines, pyrroles etc. are 7, permanent but will show some change over many hundreds of years. Alizarin Crimson is about a 6 and this is not considered to be permanent enough and is therefore classed as “moderately durable”.

All pigments are less permanent when mixed with white (‘reduced’) or used in thin layers and this is where those rated 6 and below give trouble. A 6 could drop as far as 1 or 2 when it is reduced. At this end of the scale a pigment like a PTMA violet (used in drawing inks) may last only a few days before it shows fading.

Violet Swatch

Blue Wool Scale ratings are the starting point for our chemists to assess the suitability of a pigment for artists’ use. We make up the pigment into its proposed type of colour and test it again against control samples. This testing of the pigment as a finished colour is extremely important as a pigment may perform differently once formulated into an artists’ colour. Indeed some pigments have different rates of permanence depending on the binder they are mixed with. i.e. a pigment may make a permanent oil colour when mixed with oil, but a non-permanent water colour when mixed with gum arabic.

These tests of finished colour show that colours exposed to light over prolonged periods of time can not only fade but can change hue and some may even darken.

The images below show a violet, yellow and red pigment in water colour that have faded, darkened and changed hue respectively under testing. The edge of the swatch is the un-exposed control area and the centre rectangle is the area subjected to testing. The light subjected to the swatches is the equivalent of 20 years normal daylight. Needless to say that these pigments failed our testing process.

Violet water colour swatch

Yellow water colour swatch

Red water colour swatch

How do I tell the permanence of my colours quickly and easily?

All Winsor & Newton colours are rated for quick and easy reference and you can rest assured that all of the above has been done before a colour makes it into the range.

AA   -Extremely Permanent ]
A     -Permanent  ]             Recommended as Permanent for Artists’ Use
B     -Moderately Durable
C     -Fugitive

The Winsor & Newton ratings are on the tubes and the colour charts.

You may also come across ASTM ratings which are an American system for lightfastness. Ratings I and II are recommended as Permanent. This system can also be used but may not be as accurate for actual paints as it is the pigments and not the made up colour which are tested. There are also many of the newer pigments which have yet to be rated by ASTM, we therefore recommend that you use the Winsor & Newton ratings.

For further information on pigment permanence for all Winsor & Newton ranges please see our Composition & Permanence Tables.

Permanence and longevity for Oil Painting

Grounds (primed paper, board, canvas): One of the most critical parts of an oil painting is the ground. If it is too absorbent the colour will be dull and weakly bound whilst if it is too flexible it can cause cracking. Using a good ground makes painting quicker and easier and last longer. You can use either our pre-primed and stretched canvases, pre-primed canvas rolls, canvas boards, Winton Oil Colour Sketching Pads or our specially formulated primers for paper, board or canvas.

Painting rules: There are three main painting rules which must be maintained to make a permanent and stable oil painting.

• Fat over lean – if painting in layers, each subsequent layer should be more flexible. This is achieved either by reducing the amount of solvent used or more usually increasing the amount of medium added to each layer.

• Slow drying over fast – if you are using straight colours from the tube do not use the slower dryers in the underpainting as this will cause cracking. See here for a list of drying rates. If you use a lot of white in your underpainting, use Underpainting White as this is a fast dryer.

• Thick over thin – if you are using thicker swatches of colour do not apply thinner layers over the top without scraping back as this too will cause cracking.

Solvents: Solvents are for slight dilution of the colour, the only time colours should be watery is for the first sketching in of the composition. For glazing use a medium such as Liquin Light Gel Medium, not a solvent on its own. Make sure you use an artists’ quality of solvent. Although cheaper, solvents you may find in a hardware store are not suitable as they are not pure and may contain components that will react with the colour and cause many problems.



Unfortunately, some of the ‘environmentally friendly’ solvents may not fully evaporate from the oil film and would affect long term permanence. Make sure your Turpentine is kept in full bottles in the dark to prevent it from oxidising over time and becoming non drying.

Varnishes and framing: Varnishes protect the final oil painting from the build up of dirt and grease but you must not apply them until the painting is fully dry, that’s 6 months for the thinnest of paintings and a few years for thicker ones. Alternatively the painting can be protected by a glazed frame, making sure a spacer is used in the rebate to keep the glass away from the oil surface.
 

Permanence of Acrylic Painting

There are far fewer rules for acrylics compared to oils:

Water: Do not overthin your colour with water (unless using a water colour technique on paper). For thin acrylic colour, dilute with medium (eg. Acrylic Gloss Medium) as well as water. Excess water will cause the colour to become underbound, meaning there will be insufficient binder remaining to bind the pigment. A matt or uneven finish will appear on the painting and the work will be susceptible to scuffing and damage.

Varnish: As the acrylic film approaches it final dry state, the last few evaporating water molecules leave micro-pores in the film.  These pores remain open indefinitely, meaning that the porous acrylic film can freely accumulate dust, grime, and smoke from the atmosphere.  While that grime may not seem to be much over a week or a month, it adds up over the course of years.  The best way to protect the painted acrylic film is to apply an alkali-removable varnish like Winsor & Newton acrylic varnishes.

Permanence of Water Colour Painting

Grounds(acid free water colour paper): Make sure your paper is acid free. The heavier paper is also better as it is stouter and is therefore less prone to damage. If using a lot of water, stretch your paper first. Please see our article on stretching paper for how to do this.

Colours: Provided you use AA or A colours on good quality paper, today’s water colour is no less permanent than oils. That is because the pigments are so permanent that it no longer matters how thinly they are applied.

Varnishing and framing: Do not apply varnishes to finished watercolours as the paper will absorb the resin and it will not be removable when dirty. Frame your pictures in glazed frames, ensuring there is a mount or spacer in the rebate to keep the glass away from the picture surface.

Permanence of Pastel Painting

Grounds (acid free paper or prepared paper): A rougher ground will hold more pastel, so if it can work with your technique then use Clear Gesso Base with a colour of your choice to apply to stretched paper before you start. If using coloured papers you should be aware that many will fade if not completely covered by the pastel itself.

Fixative and framing: It is recommended to use only an artists’ grade fixative for you pastel work. Use an Artists’ Fixative lightly as you work to avoid a heavy layer at the end. Frame the picture behind glass, having tapped off any excess particles and ensure a mount or spacer is used to keep the picture surface away from the glass.