A beginner's guide to watercolour mediums: ox gall & gum arabic

by Ben Platt April 06, 2022 5 min read

A Beginner's Guide To Watercolour Mediums: Ox Gall & Gum Arabic

Watercolour is arguably the easiest form of painting to get started in. The requirements compared to oil painting are minimal, and watercolours generally take up less space than acrylic. All you need are your paints, brushes, paper and water. Plus you can take advantage of a number of mediums designed specifically to affect the properties of the paint. Two of the most common but often misunderstood mediums are Ox Gall liquid and Gum Arabic. What are these two mediums and how should you apply them to your watercolour painting?

 

Ox Gall Liquid and Gum Arabic, these powerful watercolour mediums are usually available in small handy bottles.


Firstly, what is ox gall liquid and what is its use?

As the name might imply ox gall is derived from cows, specifically from gallstones taken from a cow’s gallbladder. The gallstones are refined with an alcohol to create a watercolour surfactant. A surfactant is a chemical solution that disrupts the surface tension of another substance, in this case water. It works to disrupt the water's internal cohesion making it easier for other molecules to disperse within it. The effect is a softer blend as pigment disperses with greater ease due to the increased flow of the water.

These gallstones are a byproduct of a cow's regular bodily function and are the key component to genuine ox gall solution.

It is important to be aware of the powerful nature of surfactants and that they should be used sparingly. The qualities that assist in the dispersion of pigments will also lead to blotchy and incohesive colour as the paint breaks apart entirely.

Best practice is to add no more than three to five drops per 500ml of water using a pipette, this will make a small but noticeable difference to flow of your paint and you can adjust the ratio of ox gall to water to your preference with time, but always use less to start with as a rule of thumb.

Another use for ox gall liquid is for wetting surfaces, which is increasing the ease for water to penetrate and absorb into a surface. A waterproof raincoat for example will likely have been treated with an anti-wetting chemical which repels water and causes it to bead up on the surface of the material. Whilst paper will usually absorb water very quickly, most watercolour papers are treated with a glue called size, this increases the stability of the paper, helps to prevent buckling when the paper is wet and also assists with paint flow. It should be noted that on some heavyweight papers there can be issues with water beading on the surface due to the increased amount of size found in them. This can be alleviated with the addition of ox gall liquid to your water, either used as an all over wash for wet-on-wet work or added to your mixing water for wet-on-dry.

 
You can see how the additional of a flow improver to watercolour paint can give a more even dispersion of pigment and more even blending of colour.

 

What is Gum Arabic and how is it used with watercolours?

Raw Gum Arabic in the form of chunks of crystallised acacia tree sap, ready to be ground to powder and further refined. 

Gum Arabic is the hardened sap of two kinds of acacia tree, which has also been known as gum of acacia and acacia gum. Gum Arabic has been highly valued throughout history, not only for its use as a binder for watercolour paints but because it is edible and finds itself as an ingredient in many foods, chemicals and pharmaceuticals as a stabiliser. For artistic purposes it was found to be an ideal binder for watercolours as it is water soluble and creates a cohesive paint combined with pigment and other ingredients such as honey and glycerin.

When it comes to watercolour painting, Gum Arabic has a multitude of uses, chief amongst them is slightly increasing the drying time, giving you longer to manipulate blends and washes while adding a glossy finish to dried paint. This increases the potential for creating glazes and areas of interest by adding areas of gloss to a watercolour piece.

Gum Arabic is viscous and has slight yellowish tinge but dries clear and does not affect the colouration of watercolour paints.

Another quality of Gum Arabic is how it can be used to control the spread and flow of watercolours, almost the opposite of ox gall liquid. If you apply neat Gum Arabic to an already wet patch of paper and then introduce colours you will see that the colour does not bloom out as it would usually and instead begins to feather out in a much more gradual fashion. This can be used for deliberate effect or when seeking to ensure a steadier flow in certain areas when working with wet-on-wet watercolours. 

Gum Arabic's viscous qualities give additional control to watercolour allowing for tighter control with less blooming when working wet in wet.
As Gum Arabic is used as the binder in watercolours paints, it is possible to use gum medium to make your own watercolour paints. To do so you would require the Gum Arabic such as the Winsor & Newton Gum Arabic, or in a powdered form or as solid crystals which would need to be ground to powder.

You also require vegetable glycerin which acts as a wetting agent, aids with paint flow and allows the colour to be reactivated with water more easily. A high quality honey as a moderating agent as well a natural preservative, which will prevent the watercolours from drying out entirely and cracking. With a mix of those three ingredients you will have essentially created a colourless binder. You may also add clove oil, which acts as an anti-fungal agent which will stop your colours from mouldering should that be left in incorrect conditions for too long.

Lastly you need an artist grade pigment to mix with your binder to actually create a watercolour paint. The more pigment you use the richer the colour, the less the lighter.

You can decant your watercolour paint into empty half pans or even miniature preserve jars, the paint will set but the honey inside it should keep it from going hard and it should have a slightly tacky feel to the touch. Manufacturers such as Sennelier use this method of adding honey to their watercolour as it increases the vibrancy of watercolour paints.

There are not any exact ratios for making watercolour paints, each manufacturer has their own formulas and they differ from pigment to pigment so we wouldrecommend spending some time researching the process and testing mixes. 

Mass produced or homemade, Gum Arabic is the foundation on which watercolour paints are base and we have yet to find a binder more suited to the task.

If you think you have been struggling with getting watercolour to flow then ox gall liquid might be the solution you require. If you need to add a little extra control or gloss to your work then Gum Arabic is your best choice. Used in tandem these mediums can expand the depth of techniques and allow you to fine-tune your preferred watercolour style. We hope that you have found article insightful but if you are eager to learn more then consider checking out some of our other watercolour articles below;

Ben Platt
Ben Platt


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