A few drops in your mixing water is said to enhance the colours and fluidity of your washes. Don’t overdo it though as you will get a nasty glossy or streaky effect.

I just did a Google Advanced serach and found several articles including THIS ONE.

Doug

Winsor & Newton recommend making up a solution of 10% gum arabic 90% water and use this with your colours as you would water alone.

Hope that helps, let us know how you get on

Regards
Tony

I know, it’s hard not to have an exact starting point. I’m a very literal person and just go nuts with being told “just use ‘some’!”

Does it work? Yes. But, I was remembering when I first started using it that I didn’t notice any difference at all – I put a few drops in my mixing water. I was just getting really into watercolors.
Now, when I look at my paintings from then, I can tell exactly which I used it with – well, the ones that I probably used quite a bit with – they’re so much shinier.

I like to have a few drops in my mixing water all the time now. When I paint, I like to make a puddle of water in the space I’m working on (say a petal of a flower) and then float paint into it. I find that when I put Gum Arabic in the water, that puddle stays exactly where it’s supposed to much easier – it doesn’t seep out once it sinks into paper. I also get harder edges with it – sometimes a good thing, sometimes not.