All about Pigments Dyes and Stains
Wednesday 13 January 2010
Michael Huntley explores the theory of coloured finishes for furniture
Some people use only clear materials as a surface finish. However, the ability to apply colour to a finish can enhance the appearance of an item. The ability to swing a colour can redeem an irregular piece of timber or remove a blemish. It is said that a good polisher can save poor cabinetmaking, but a poor polisher just ruins good cabinetwork.
Too often the phrase I like the natural finish is an excuse which hides the thought Colouring a finish is too difficult to understand. Well, it is difficult and it is time consuming but I hope this article encourages you to go out and buy some colours and give them a try.
Let us start by clarifying what I mean by colours. Colouring materials for furniture come in a bewildering range of formats. The first thing to understand is that there are three types of material that you might encounter: pigments, dyes and stains.
Each of these may be bought or may be mixed with different carriers or vehicles. The vehicles encountered in the furniture world are spirit, oil and water. There are also other additives which might, for example, alter the drying time, or the workability, or the resistance to ultra-violet (UV) light.
Pigments have comparatively large particle size and do not dissolve. They are usually bought as powders and are mixed with a clear resin which when dry binds them to a surface.
They can be mixed with wax polish to tint the polish.
They will also be found in paints which might be used for touching up blemishes. Both acrylics and watercolours can be used for this purpose. Oil paints dry too slowly to be used without long intervals between applications.
Please be aware that some pigments are very toxic. It is unlikely that you would come into contact with them but ALWAYS read the label and check the data sheet.
Dyes and stains
Dyes are organic molecules that absorb particular wavelengths of light, giving rise to perceived colour. They may be animal, vegetable or mineral. The particle sizes of dyes are on a molecular level that allows them to penetrate substrates such as timber.
In 1856 William Perkin produced the first synthetic dye. Many dyes are now synthesised from aniline which is a chemical derived from coal tar. The colours in aniline dyes used to be considered fugitive because they faded, but there are now varieties such as Orasol which are very stable.
The term stain is used to describe any material that adds colour to wood while still maintaining a high degree of transparency. Apart from attempts to make a cheap wood look like an expensive timber, stains are very useful in matching variations in boards and blending sapwood to the colour of heartwood.
Every school child is familiar with the colourwheel on which, starting at 12 noon, colours are arranged in the following order: red, orange, yellow, green, blue, indigo, violet - the colours of the rainbow.
A complementary colour is one that is directly opposite to the colour being considered. For example the opposite of red with a touch of orange is green with a touch of blue.
When light falls on a surface it may be reflected, transmitted through the object or absorbed by the object. If some wavelengths are absorbed more strongly than others then the object will appear to have the colour complementary to the wavelength absorbed. For example, strong absorption of blue will make the object appear yellow and strong absorption of red will make the object appear bluish green.
Choosing colour system
The type of colour that you use is based on experience but a newcomer needs to be aware that whatever system is chosen, it must be possible to remove it if it all goes wrong.
Certain systems are not reversible, such as chemical colouring. There is one exception to this rule and that is bleaching. You can always make a lighter area darker, so if bleaching were to go wrong you could lay on a dark colour, but it does require a lot of experience to rebuild a bleached area so avoid bleaching until you are quite sure how to do it.
Oil stains are hard to control and both oil and spirit stains are difficult to remove, so they are not good for the beginner. That leaves those that use water as a vehicle, and information on water stains will be posted soon.
I said that one should aim to use a colour that can be easily removed from the surface. One way to make removal easier is to seal the surface and then use the colour within later layers of clear film. Colour can be painted on within the polish layer. If it all goes wrong the polish can be cleaned off with a solvent and you can start again. I will soon be describing that process as well.
Finally, you could opt for a semi-transparent coloured polish and I will be showing examples of those too.