This masterclass shows how to slow down the drying time of watercolour using Gum Arabic, which is especially useful when painting en plein air. Gum Arabic is the binder in watercolour paint and, by adding a bit to your watercolour mixture, you will slow the drying time of your mixture versus watercolour diluted only with water. A swatch of watercolour without any additional Gum Arabic shows how watercolour behaves with water alone, then the Gum Arabic is added directly to the paint. It is easy to see that the paint mixed with Gum Arabic sits on the paper slightly differently: the gloss and transparency is increased, the paint moves more slowly on the paper and it remains open to work with for longer. You can also add a small amount of Gun Arabic to your mixing water and introduce it to your paint that way. Finally, if you apply a watercolour and Gum Arabic mix to paper and then apply watercolour on top of that wet layer, you can control the spread of colour more than if you didn’t use a Gum Arabic mix in the base layer.