Foraged cherry tree gum. Tree gum was historically used in the Baltic as part of recipes to make imitation amber for jewellery and ornaments and some large lumps I find look good enough to set in silver. Most, however, are destined to be used for my watercolur medium.

Taken from her book, Found and Ground (published by Search Press), learn how to make your own watercolour medium using foraged tree gum with Caroline Ross.

Years ago, while studying traditional art materials with Daniel Chatto on his course ‘The Stuff of Painting and Drawing’, I heard him mention in passing that cherry tree gum had been used historically as a paint binder in place of gum Arabic. This piqued my interest as a forager and an artist as I searched for natural art materials and media to replace synthetic products in my art practice.

The techniques used to make watercolour medium are simple, and will be familiar from making your paints. Once you’ve gathered even a teaspoonful of gum, you’ve got enough to make some medium. Unless you are going to use all your medium while it is fresh (within a day or two), you need to add a few drops of anti-fungal essential oil to the mix or store it in the fridge.

About foraged tree gums

Authentic gum Arabic comes from Senegal, where it is harvested from acacia trees. Some other acacias, as well as fruit trees of the Prunus and Eucalyptus genera, sometimes exude a sticky gum from fissures in their bark.

This gum can be collected without harming the tree at all if you follow some simple guidelines: gather where it is abundant, and take only what is on the surface of the bark, never cutting into or picking at the bark itself.

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Where and how to collect tree gum

Suitable trees include cherries, plums, gages, damsons and various acacias.

Cherry tree gum produces a light, gel-like medium with a matt finish, whereas the more traditional gum Arabic from acacia gives a honey-like consistency that binds pigment well and gives a little sheen to the paint finish.

The gum is softer after rain, when it can be scooped off with fingers or a spoon. In dry weather it will dry solid, and you’ll need a knife to remove it.

Carry it home in a tub or plastic bag, then allow it to dry thoroughly before storing it. It lasts indefinitely if kept in a paper bag or cardboard box.

In the spring, as the sap rises, the gum can be a clear, pale yellow or even colourless. This a real find, as the absence of a yellow tinge means the gum can be used to make white, mauve and blue paints, where a yellower or amber-coloured binder would muddy the tones with the complementary colour. You may also find clear droplets of gum like little teardrops exuding from fruits in the summer, caused by wasps piercing their skin. These too can be gathered to make binder for the very finest pale blues.

In late summer and autumn, the gum can become darker in tone – amber, deep brown or even almost black. It picks up specks of bark and tannins from the wood as it passes through, and these give the gum its colour.

All colours of gum are useful, and once dry, it’s worth grading them into separate shades for different uses. It is possible to use the paler second and third flushes of gel from the cherry tree gum to make watercolour medium, however dark your lumps of fruit tree treasure.

Making your own watercolour medium

You will need:
  • Solid dry tree gum – either bought lump gum Arabic; foraged cherry tree gum; acacia or eucalyptus tree gum; or other non-coniferous tree gum
  • Water
  • Pestle and mortar
  • Glass jar
  • Spoon
  • Mesh bag
  • Saucepan
  • Tea strainer
  • Container
  • Honey

I’m using cherry tree gum here, but you can use whatever bought or foraged gum you have.

The medium produced from cherry tree gum will not be as sticky or as glossy as gum Arabic, so be prepared to add up to a quarter more medium to your paints, to adjust the honey/sugar ratio until you get it just right for your needs. Alternatively, paint a top layer of the medium over your work to add shine, if needed.

Step one

Start with half a teaspoon or so of dried gum.

Step two

Using a brass pestle and mortar within a mesh bag (this prevents fragments flying out), break up the pieces until they are like sand.

Step three

Put the smashed gum into a jar and half fill it with water. Stir and leave overnight.

Step four

In the morning, you’ll find the gum has turned into a gel or has begun to dissolve. Pour this into a saucepan and warm it on a low heat for half an hour or so, until the gel is the consistency of runny honey (you can add more water if there is not enough for it to be stirred easily).

When it has cooled a little, place a tea strainer over a container and pour the gel through. The little flecks of bark and other detritus should be left behind in the strainer, you can just wash these away.

Step five

Add a rewetting agent such as honey (vegans can use glycerine or powdered sugar dissolved in a little warm water). You need approximately one-part runny honey to nine parts gel. Stir the mixture well.

Step six

Decant the mixture into a spotlessly clean jar. I like to sieve it again through a finer mesh strainer into the jar at this point.

This is your homemade watercolour medium, which you can use in the same way as you would shop-bought medium, or one you have made yourself with liquid or powdered gum Arabic.

Keeping things clean

Some artists add a drop of anti-fungal essential oil to the medium, which also has the benefit of smelling lovely.

I leave out this step and instead use spotless bottles and jars which I store in the fridge, with equally good results.

Making additional batches

When processing foraged gum, there will probably be some lumpy gum gel left in the strainer after step four.

This can be reused. Just return it to the saucepan, add a cupful of hot or just-boiled water, and repeat the cooking, cooling and straining processes.

You can do this up to two times. Each batch will be a little paler. You can either add them all together or keep them graded for different colour paint making. They are not as adhesive as the first medium but produce a very matt binder.

Storing your finished watercolour medium

Once you’ve filled your vessel, label it well with the ingredients you used and the date you made it.

It will look and smell delicious, so I always suggest adding a ‘Do Not Eat!’ label before putting it in the fridge.

Found and Ground by Caroline Ross

Found and Ground by Caroline Ross. ISBN 9781800920996. RRP £15.99

In Found and Ground Caroline details a more sustainable and fulfilling approach to painting, explaining how to create professional-quality paints using colour from the earth itself. The book covers how to make a series of simple natural paints such as watercolour, gouache, tempera, and glair.

Find out more and *order your copy for just £12.79 by


*Please note that this book only ships to UK addresses

Now try making your own historical inks with Alan Bickley and Fiona Phipps


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